Sugar and Alcohol

Sugar and Alcohol Concentration

• Sugar Concentration
• Alcohol Concentration

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Sugar Concentration
Grape sugars, specifically glucose and fructose, are used by yeast in alcoholic fermentation to create energy for growth, while also producing carbon dioxide (CO2) and ethanol as byproducts. The concentration of sugar, typically measured in degrees brix/baume, is generally indicative of the percentage of ethanol that will be created in fermentation.  
​
​Ideal sugar concentration prior to fermentation: 20-25° Brix

• Sugar concentrations of 25-30% cause ethanol production per gram of sugar to decline, and may cause “stuck fermentations,” which is when the fermentation prematurely terminates (Jackson, Wine Science).
• High sugar content can cause elevated amounts of acetic acid. [2]
• Deficiencies will cause flavor issues because of low alcohol concentrations.

Alcohol Concentration 
In wine, ethanol is a flavor in itself. It is a solvent for flavor compounds, and reacts with organic acids and other aroma precursors to create aroma compounds.  Its impact on fermentation varies by percentage, as all alcohols are toxic to varying degrees and eventually inhibit fermentation.  Jackson Notes in Wine Science:

Ammonium transport and inhibition of general amino acid permeases decrease as alcohol content increases, however, this can be mitigated by enrichment with unsaturated fatty acids like yeast hulls. 

Ethanol’s ability to stop fermentation is taken advantage of in the production of fortified wines.  In this process, a distilled wine/unmatured brandy is added to fermenting must or wine.: 

• In port wine production, brandy is added early during fermentation to retain about half the sugar content of the must. This leaves the wine with the aromatic attributes typical of early fermentation. For example, young port is likely to be higher in acetic acid, acetaldehyde, and acetoin content, but lower in glycerol, fixed acids, and higher alcohols than if it had been fermented to dryness.
• In sherry production, wine spirits are added at the end of fermentation to inhibit the growth of acetic acid bacteria (which occurs at ~15% ethanol) and yeasts (which occurs at ~18% ethanol) during solera aging. 

Ranges: Maximum of 13-15% ABV
Suppression of sugar uptake may begin at ~2% ethanol.  This can also be influenced by the fermentation temperature.
Higher (fusel) alcohols are more inhibitory than ethanol; their lower concentration in the fermentation substantially limits their toxic influence.

Pre-Fermentation Sugar and Alcohol Content Adjustments

​Sugar concentrations may need to be increased if grapes do not reach the desired sugar ripeness, even though they have reached phenolic maturity, or if preharvest rains cause “rain swelling” and juice dilution. This typically occurs pre-fermentation. An increase in sugar concentration is necessary because sugar content dictates the final alcohol concentration of the wine.

• Chaptalization
• Reverse Osmosis
• Cryoextraction
• High-Vacuum Evaporation (HVE)

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​Pre-Fermentation Sugar Adjustment: Chaptalization (the addition of sugar)

Usage: Named after French chemist Dr. Jean-Antoine-Claude Chaptal, who advocated for (not invented) its usage in 1801, chaptalization is the process of adding sucrose (table sugar) to wine to increase the brix in grape must, which in turn increases a wine’s final alcohol without adding flavors to the wine.  

• It is generally only permissible in cool climate regions (Winkler I and Winkler 1b) where grapes regularly have difficulty achieving the desired minimum sugar content.  
• Though it can also be used to counteract the impact of juice dilution caused by preharvest rains, this is typically not legal. 
• Secondary impacts include the synthesis of other sugar-related compounds, including glycerol, succinic acid, 2,3-butanediol, and some aromatically important esters (Jackson, Wine Science).

Process: Sugar is dissolved into grape juice near the end of yeast growth (about 2-–4 days after the commencement of fermentation) in order to not disrupt fermentation of the grape’s constituents. 17 grams of sucrose yields approximately 10 grams of ethanol (Jackson, Wine Science). 

Pre-Fermentation Sugar Adjustment: Reverse Osmosis

Usage:  Reverse osmosis removes water from the grape must, thereby increasing concentration of everything else, including brix and acidity.   However, desirable aroma compounds, including small, highly volatile water-soluble compounds, may also be removed.  This can be mitigated with the addition of untreated juice or reintroduction of the volatiles removed with water (Jackson, Wine Science). Development of filters with improved selective permeability may eliminate this problem. 

Chaptalization compared to reverse osmosis [3]:  Duitschaever et al. (1991) examined the impact of both processes on riesling wine, where Riesling must was concentrated using reverse osmosis to three different levels of soluble solids by increments of 2 °Brix, and the composition of must/wine compared to that of the must/wine by chaptalization. Beyond being an alternative to chaptalization, it was found that: 
Reverse osmosis treatment increased the concentration of soluble solids, including the acids. The pH was not affected. 

• Chaptalization only increased sugar concentration. 
• Irrespective of the method, the pH was higher, and the concentration of the acids were lower in the wines than in their respective musts.
• The volatile acidity increased linearly over the concentration series for reverse osmosis, but remained constant for the chaptalization wines. 

Process [4]:

• Must is prepared to decrease the number of suspended particles (turbidity) to less than 200 Nephelometric Turbidity Units (NTU). 
• Semi-permeable membranes are used to filter the must.

For additional insight into dealcoholizaiton by filtration:  
Youssef El Rayess & Martine Mietton-Peuchot (2016) Membrane Technologies in Wine Industry: An Overview, Critical Reviews in Food Science and Nutrition, 56:12, 2005-2020, DOI: 10.1080/10408398.2013.809566

Pre-Fermentation Sugar Adjustment: Cryoextraction
According to Jackson in Wine Science:

Usage: The freezing of grapes, which are then crushed and pressed while frozen, increases the concentration of grape constituents by decreasing the amount of water in the grape must. This process can be used to augment the sugar and flavor content of grapes in the production of sweet table wines. 

Process

• Grapes are frozen, then crushed and pressed while partially frozen.
• The water in grapes cools and forms ice, and the dissolved substances become increasingly concentrated in the remaining liquid.
• Since more mature grapes have greater sugar content, they freeze more slowly than immature grapes. Preferential extraction of juice from the more mature grapes can then be achieved. Temperatures down to 15 °C increase solute concentration; temperatures between 5 °C and 10 °C are generally sufficient to remove unwanted water. 
• Cryoextraction appears not to produce undesirable sensory consequences. 

Pre-Fermentation Sugar Adjustment: High-Vacuum Evaporation (HVE) [5]
A concentration technique based on water extraction by its evaporation under high vacuum (19-39 mbar) and at an ambient temperature (20 °C) that prevents any must component degradation.

Post-Fermentation Sugar and Alcohol Content Adjustments

• Sugar Adjustment: (Back) Sweetening
• Alcohol Adjustment: Reduction of Alcohol

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Post-Fermentation Sugar Adjustment: Sweetening
Historically, sweet wine contained honey or boiled down must, as naturally sweet wines were rare and typically required highly botrytized grapes. There was a lack of understanding on how to manipulate fermentation. The usage of distilled alcohol to stop fermentation is a comparatively recent innovation. Modern technology and science now allow for more fermentation manipulation without additives. 

Common Sweetening Techniques

• Sugar may be added, as is the case for sparkling wines. 
• Residual sugar caused by incomplete fermentation. 
• Sweet reserve (süssreserve): Adding partially fermented or unfermented grape juice. Jackson in Wine Science noted the following production methodology:
  
  • The base wine is typically fermented dry and sweetened just before bottling. To avoid microbial contamination, both the wine and sweet reserve are sterilized by filtration, or pasteurized, and the blend bottled under aseptic conditions, employing sterile bottles and corks.
    
  • Preparing and preserving sweet reserve may include:
    • Keeping a small portion of the juice unfermented so that the resulting wine possesses a consistent varietal, vintage, and geographical origin. 
    • Unfermented juice has microbial activity restricted by cooling to 2 °C, applying CO2 pressure, pasteurizing, or sulfiting to above 100 ppm of free SO2 after clarification. If sulfiting is used, the juice is desulfited by flash heating or sparging with nitrogen gas before use. 
    • The juice may be concentrated by reverse osmosis, cryoextraction, heat or vacuum concentration.
    • Partial fermentation, with the yeast activity terminated by chilling, filtration, centrifugation, or by trapping the carbon dioxide released during fermentation. 

Pre-Fermentation Alcohol Adjustment: Reduction of Alcohol
Dealcoholization may be used to remove some or most of the alcohol from wine, and is performed at the completion of fermentation.  

The common techniques:

• Reverse osmosis
• Vacuum distillation.  
• Removal by spinning cone column
  
  

Less common techniques:

• Heat-induced evaporation
• Volatilization with carbon dioxide
• Dilution with water.  
  
  

Experimental techniques: 

• Lower alcohol producing Saccharomyces cerevisiae strains.  In this process, the yeast create glucose oxidase which extracellularly oxidizes b-D-glucose into D-glucono-d-lactone and gluconic acid (GA).  This prevents its entry into glycolysis thereby diverting a portion of the sugar’s carbon away from ethanol. [6]  
  
  For great insight into this topic, read: 
  Malherbe, D. F. (2010). Characterization and evaluation of glucose oxidase activity in recombinant Saccharomyces cerevisiae strains (Doctoral dissertation, Stellenbosch: Stellenbosch University) http://scholar.sun.ac.za/handle/10019.1/4008
• Select strains of Saccharomyces uvarum and Metschnikowia pulcherrima have also been shown to create lower alcohol concentrations, as seen by the Australian Wine Research Institute (AWRI) 1149 and AWRI 3050.7   

We will examine non-alcoholic wine in a future issue of Hawaii Beverage Guide. 

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Acidity: pH and Titratable Acidity

Beyond providing a fresh or lively taste in the final wine, acidity also has indirect influence on a wine’s final flavor. This includes:

​Acidity’s Influence on Fermentation [8]

Swiegers et al. (2005) notes that acidity, particularly pH, influences the effectiveness of some antioxidants, antimicrobial compounds, and enzyme additions and:

• Ideal Levels
• Aroma
• ​Color
• Stability and Aging Potential

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Levels

• Malolactic fermentation can be suppressed if acidity is below 3.2. [9]  

​Aroma

• Enhances the production and stability of fruit esters (Jackson, Wine Science). 
• Monoterpene concentration of geraniol, citronellol, and nerol may rise at low pH values, whereas those of linalool, α-terpineol, and hotrienol may fall (Jackson, Wine Science). 

Color

• Lower pH (more acidic) can increase the polymerisation of the color pigments, affect the color intensity and hue of red wine. 
• Higher pH (more basic) reduces oxidative and browning reactions.
  

Stability

• The survival and growth of all microorganisms; lower pH (more acidic conditions) are more inhospitable to unwanted microbes and may decrease the need for sulfur dioxide.
• The solubility of proteins and tartrate salts.
• The effectiveness of bentonite treatment.

Aging potential.

• Higher acidity allows for longer aging potential, as it provides better microbial stability, especially because acidity decreases over time.  

Types Of Non-Volatile Organic Acids in Grapes and Wine
And their usage in Acidification  [10]

Tartaric acid and malic acid make up 90% of the titratable acidity (TA) in grape juice. These acids vary in strength, as measured by the acid dissociation constant (pKa value). 

These acids can be low in quantity. This is more common in warm to hot viticultural regions, due to the extensive metabolism of malic acid near the end of grape maturation [19], and serves to limit the growth of unwanted microorganisms and enhance the flavor, as wine made from musts fermented at a low pH are generally preferred (Jackson, Wine Science).   

General Adjustment Process [20]
The addition of acid to grape juice, must or wine will decrease the pH and increase TA of the wine. The amount of acid needed to correct the acidity deficiency depends on the total acidity, pH, and buffer capacity of the juice, must or wine.  The addition of tartaric, malic and citric acids will also affect the pH, TA and taste of the wine differently.

For an in-depth guide to acidification:
Scollary, G., & Fahey, D. (2020). Acidity Management of Grapevines and Wines. New South Wales Government - Department of Trade & Investment. https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0007/1265227/Acidity-management-of-grapevines-and-wines.pdf

• Tartaric Acid
• Malic Acid
• Citric Acid
• Other Non-Volitle Acids
• ​Other Acidity Adjustments
  

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Tartaric Acid 
The primary acid in grapes, tartaric acid develops naturally.

Impacted by: Metabolized by the vine during growth or by yeast during fermentation.

Range: The maximum concentration at véraison of 20+ g/L, which decreases to 4–15 g/L at harvest because of the increase in berry volume.

pKa Value [11] : pKa1=2.98 and pKa2=4.34
Usage in Acid Adjustment

• Used to decrease the pH by inducing the precipitation of excess potassium (as a bitartrate salt). This allows it to significantly reduce pH compared to other acids, as dictated by its by dissociation constant (pKa), especially when added to wines high in potassium content. Crystal formation results in most of the tartaric acid being lost due to precipitation (Jackson, Wine Science). 
• Has a fresh, crisp taste and high microbial stability.

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Malic Acid 
Primarily produced by grapes during growth.

Impacted by: Saccharomyces cerevisiae, which can degrade 3–45% of total malic acid during fermentation. Most strains of Schizosaccharomyces pombe and Schizosaccharomyces malidevorans can completely degrade it to ethanol and CO2.

pKa Value [12] : 3.4 and 5.03

Usage in Acid Adjustment
Malic Acid (in L or DL forms)

• Used to adjust total acidity, more than pH, and is similar in process to adding tartaric acid. 
• Disadvantage: Can cause problems with microbiological stability.

Citric Acid 
Primarily produced by fermentation but in small amounts. 

Impacted by: The tricarboxylic acid (TCA) Cycle, as pyruvate is decarboxylated and reacts with Coenzyme A to yield acetyl-CoA. [13]

pKa Value:  2.79 [14]

Usage in Acid Adjustment 

• Used to facilitate iron stabilization, and can assist in preventing ferric casse (cloudiness) (Jackson, Wine Science).  It is also used with white wine, as it can provide a fresher mouthfeel.
• Drawbacks: As a substrate for bacteria, additions should be limited to 0.15 to 0.2 g/L with varying limits by country. In red wine, it lowers the sulfur dioxide level and increases the potential for spoilage by lactic acid bacteria, which can lead to undesirably high concentrations of diacetyl (Jackson, Wine Science).

Succinic Acid

• Primarily generated during the fermentation process, its contribution is more to TA than pH. 
• Impacted by: The amount formed is dependent on the yeast strain used, but there may also be other factors involved including: A moderate to high fermentation temperature (20-28 °C); a sugar concentration of 200-240 g/L; a moderate amount of metabolically available nitrogen; the presence of flavonoids and unsaturated long-chain fatty acids; aeration of the fermentation juice (Jackson, Wine Science).
• pKa Value [17]: 4.21

Keto Acids (present only in trace amounts in grapes)
Concentrations are higher in wines as a result of fermentation (Whiting 1976, Fowles 1992, Radler 1993, Boulton et al. 1998).

Plastering with Gypsum 

• Used to convert some of the potassium bitartrate to the free acid form. 
• Drawbacks: An old form of acidification that is rarely used, because it increases the wine’s sulfur content and is only approved for the production of  some dried fortified wine from Spain.

Cation Exchange Resins

• Used to acidify high-volume wines that are high in potassium, by using a “resin” to remove potassium ions (K+) from the wine and exchange it for H+ ion form, thereby lowering the pH.  Typically, only about 20% of the wine is treated to a low pH (about 2.7-2.8) and then mixed into the remaining wine because metallic flavors may appear. Though previously used for low-end wines, it is now applied to some premium wines. The perceived advantages of cation exchange include: its increased effectiveness in correcting acidity and pH, rather than adding tartaric acid and risking  tartrate instability; its relatively lower cost compared to adding tartaric acid; and no negative impact on taste. 
• Drawbacks:  Though potentially more cost-effective in the long run, it has high upfront costs, and the pH change it creates is somewhat unpredictable.
• For more on the usage of an ion exchange column read: 
• Patterson, T. (n.d.). Really, Really High pH Remedies. Wines & Vines Analytics. https://winesvinesanalytics.com/sections/printout_article.cfm?content=68770&article

Volatile Acids

• Acetic Acid
• Lactic Acid

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Acetic Acid

• Primarily produced by oxidative spoilage resulting from a combination of oxygen/ethanol/acetobacter. A small amount is formed in fermentation. In wine, acetic acid exists as the neutral molecule, making it a “volatile” acid, meaning that if the opportunity arises, it will assist in spoilage, resulting in the aroma of vinegar.
• Impacted by: Yeast strain
• pKa Value [16]: 4.76

Lactic Acid 

• Primarily produced by malic acid degradation during malolactic fermentation, this process reduces the acidity, softens the taste, and increases the complexity of wine.
• Impacted by: malolactic fermentation practices 
• pKa Value [15]: 3.86
  
  

Usage in Acid Adjustment
Used to increase the acidic taste, and enhance the perception of body in the wine. It decreases pH more predictably compared to using tartaric acid, and is not affected by cold stabilization, since the potassium salt is soluble. It may be added just before bottling without cause for precipitation, and increases the formation of lactic esters that contribute to a wine’s aroma. 
Drawbacks: As the weakest permitted acid, a larger volume of acid is required for the same pH decrease. 

​Measuring Acidity of Wine

The most common measures of acidity are pH and titratable acidity (TA). [18 ]Unfortunately, there is no predictable measurement of the ratio between pH and TA. According to Jackson in Wine Science, the typical ranges are: ​

• Titratable Acidity/Total Acidity (TA)
• Potential Hydrogen (pH)
• Volatile Acidity (VA)

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Titratable Acidity (TA) 

• Measured in grams/liter, TA attempts to measure the total acidity of wine.   
• Typical Range: Between 5.5 and 8.5 mg/liter
• White wines are generally at the higher end of the scale.
• Red wines are at the lower end. 

For more on the relationship between pH and TA
Australian Wine Research Institute. (n.d.). Acidity and pH. The Australian Wine Research Institute. Retrieved April 21, 2022, from www.awri.com.au/industry_support/winemaking_resources/frequently_asked_questions/acidity_and_ph/ 

Potential Hydrogen (pH)
pH measures the H+ ion concentration in a solution.  It ranges on a scale from 0-14, with 7 being neutral (the pH of water), 0 being the most acidic, and 14 being the most basic (least acidic).

Ideal Juice or must acidity: 

• Lower values (more acetic) than the final desired pH and TA are usually preferred, because the pH often increases slightly during or after fermentation (frequently as a result of tartrate crystallization). 
• Juice above pH 3.4, especially for white wine, is often adjusted prior to fermentation to improve the fermentation environment and avoid large adjustments following fermentation.

Typical Wine pH Range

• White wine: 3.1 and 3.4 
• Red Wine: 3.3 and 3.6 
  Red wines have higher pH values (are less acidic) than white wines, as red grapes are more frequently grown in warmer regions, and therefore tend to have lower malic acid contents at harvest. Additional losses in acidity of red wine are caused by  increased levels of potassium extracted during the extended maceration of red wines. This causes additional conversion of tartaric acid to its nonionic salt form, which then precipitates out during fermentation.

Perception of Flavor 
According to Jackson in Wine Science:

• Sour wines: pH of 3.1 or below 
• Flat or lacking acidity: pH above 3.7​

Volatile Acidity
Measures the quantity of acetic acid (the primary acid in vinegar) in wine

Acidity Adjustment: Deacidification [20]

​More common in cool climate regions where grapes have difficulty ripening, deacidification is typically performed after fermentation, allowing the typical decrease in wine acidity to occur; however it can be done prior to fermentation to make large corrections in acidity. The multitude of methods to deacidify wine can be broken down into biological deacidification, which utilizes microbes to break down acids( as is the case of malolactic fermentation), and physicochemical deacidification, which is the process of neutralization by a salt like calcium carbonate, potassium carbonate, or Acidex.

• Physicochemical Deacidification
  
• ​Biological Deacidification

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Physicochemical Deacidification [21]
The process of adding a base to neutralize the acid, which then forms a salt which can be precipitated out.  

General Process: Juice or wine that is relatively low in dissolved solids is cooled to below 4 °C. The base of calcium carbonate or potassium carbonate is then dissolved in water or in some of the wine before being integrated over the course of at least 30 minutes. The juice/wine is then allowed to settle for several hours at <4 °C before being racked/filtered at the same temperature. If tartrate removal is excessive, the resulting increase in pH may leave the wine tasting flat and susceptible to microbial spoilage.

Finely ground calcium carbonate (CaCO3)

• Usage: This is the most common technique of deacidification 
• Mechanism: CaCO3 precipitates out as calcium tartrate (CaT). 
• Disadvantages: As CaT is slow-forming, crystals may not precipitate out of solution for several months, whereas potassium-based carbonates can precipitate out more quickly (AWRI, Deacidification FAQ). Additionally, the formation of calcium malate may produce a salty taste. 

Potassium-based carbonates of potassium carbonate (K2CO3) and potassium bicarbonate (KHCO3) 

• Usage: Potassium bicarbonate is recommended over potassium carbonate, as the bicarbonate is a weaker base and is therefore the more gentle deacidification agent (Rankine 2004). 
• Drawbacks: Considerable CO2 can be evolved during the deacidification process, which can cause excessive foaming. The bicarbonate salt will tend to cause the least foaming of the three deacidification agents.  Potassium tartrate is more expensive, whereas potassium carbonate is prohibited in several countries.

 
Double-salt deacidification [22]

• Usage: Used for must with high TA and pH, this method speeds up the precipitation of calcium tartrate, thereby primarily neutralizing tartaric acid, and facilitates the partial precipitation of calcium malate. The original concept of a double salt stems from an 1891 report by C. Ordonneau, titled “De l' acidite des raisins verts et de la preparation de l'acide malique.” Since then, there is an exponentially better understanding of science and the reaction kinetics.
• Mechanism: Modern research has not shown the existence of a calcium malate-tartrate double salt as proposed by Ordonneau. Cole and Boulton (1989), found that calcium tartrate and calcium malate precipitated separately in an interrelated process, where both act as seed particles for calcium malate precipitation. In the winery,  this process is accomplished by treating ~10% of the wine or clear must with calcium carbonate (instead of all of the wine as with a single salt process) to raise the pH to above 5.1 to assure adequate dissociation of both malic and tartaric acids (Steiner, 2020). The resulting reaction is a theoretical 1:1 yield of tartaric and malic acid removal (Steiner, 2020). Precipitation is then done by racking, filtration, or centrifugation, after neutralization removes the excess potassium with acid salts, and the added tartaric acid lowers the pH to an acceptable value. The remainder of the wine is slowly blended back into the treated portion, with vigorous stirring. Subsequent crystal removal occurs by filtration, centrifugation, or settling. Stabilization may take 3 months, during which residual salts precipitate before bottling.
• Drawbacks: The technique sometimes only removes tartaric acid, or may produce little reduction in malate concentration. It requires more specific attention and has increased difficulty, and cannot be used with malolactic fermented wine (Steiner, 2020).

Ion-exchange column

• Usage: High-volume wine production, or wine that needs significant adjustment.
• Mechanism: Wine is passed through a column containing anion-exchange resin to:
• Exchange tartrate ions with hydroxyl ions (OH), thus removing tartrate from the wine. The hydroxyl ions released associate with hydrogen ions to form water. 
• Exchange malate with a tartrate-charged resin,23 with the excess tartaric acid subsequently removed by neutralization and precipitation. 
• Drawbacks: Legal restrictions, high cost of equipment, and the tendency to remove flavoring and color from the wine.

Pre-fermentation deacidification techniques: Amelioration
The dilution of juice with water and sugar, lowers acidity; however, it  is illegal in many countries. If used, its drawbacks include a reduction in aroma, flavor, color, and varietal character (Steiner, 2020).  The United States Alcohol Trade and Tax Bureau (TTB 27 CFR, part 24 Section 23.178) limits amelioration based on the final fixed acid content not being reduced below 5.0 g/L, and the maximum amount of material not exceeding 35% v/v.

Pre-fermentation deacidification techniques: Blending with juice of lower acidity and higher pH. 

For more on deacidification
Steiner, T. E. (2020). Acid management of must and wine - Ohio State University. Ohio State University . Retrieved April 20, 2022, retrieved from https://ohiograpeweb.cfaes.ohio-state.edu/wine-making/pre-fermentation-practices  

​Biological Deacidification
Yeast choice during primary fermentation, as some yeast like schizosaccharomyces pombe will degrade malic acid.  For more on yeast function read: The Hawaii Beverage Guide article on wine yeast at hawaiibevguide.com/wine-microbes 

Malolactic Fermentation
Malolactic fermentation is the degradation of malic acid into lactic acid by oenococcus oeni or other lactic acid bacteria.  For more on malolactic fermentation read: https://www.hawaiibevguide.com/wine-post-fermentation-flavor-adjustments.html#%E2%80%8BMalolactic_Fermentation 

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Phenolic Content

For insight into Wine Polyphenols:  ​A Guide to: Wine Polyphenols

• Phenolic Influence on Fermentation
• Phenolic Additions
• Removal of Excessive Phenolics

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Grape phenols have varying impacts on fermentation. Jackson in Wine Science provided the following examples:

• Anthocyanins stimulate fermentation, whereas procyanidins in white grapes can be slightly inhibitory. 
• Film formation in fino production may be activated. 
• Phenolic esters of gallic acid are toxic, whereas others, such as chlorogenic and isochlorogenic acids, may stimulate fermentation. 
• In sparkling wine, phenols suppress yeast metabolism during secondary fermentation. For more on this impact, see hawaiibevguide.com/sparkling-wine. 
• Phenols may be modified by yeast action. For example, ferulic and p-coumaric acids may be decarboxylated to aromatic vinyl phenols (4-vinyl guaiacol and 4-vinyl phenol, respectively).24 
• Tannins may also reduce astringency, generate a smoother mouth-feel, reduce the likelihood of oxidative casse, and limit the formation of undesired sediment following bottling (Jackson, Wine Science).  

Phenolic Additions
Most phenolic adjustments are done to influence color and aroma.  These include:

Pre-fermentation additions 
Most phenolic additions, in the form of increasing extraction, as discussed in the February 2022 issue of Hawaii Beverage Guide (hawaiibevguide.com/wine-making-pre-permentation-process), are performed through a maceration process.  Additional approaches include:

Enological tannin additions including aging in new oak or oak adjunct additions to the fermentation
Process: Aging in new oak or using oak tannins in the form of staves, chips, and powdered tannins to simulate barrel aging in inert containers can be used to provide better color depth, improve color stability and improve aroma.  We will discuss the detailed influence of oak’s constituents on wine in a future issue of Hawaii Beverage Guide.

Post-fermentation color adjustments
Micro-oxygenation of red wine
Process: Oxygen is slowly or periodically added to favor the polymerization of anthocyanins with tannins. 

For more on the influence of oxygen on grape phenolic content see Influence of Oxygen
https://www.hawaiibevguide.com/wine-fermentation-environment.html#physical-factors

Removal of Excessive Phenolics
Similar to adding phenolics, their removal influences color and aroma. The causes of excessive tannins result from a multitude of reasons.  Jackson in Wine Science noted the following: 

• Oak chips or shavings may cause phenolic instability due to over extraction of ellagic acid(Pocock et al., 1984). 
• Excessive amounts of leaf material in the grape crush, another atypical source of phenolic instability, may cause flavanol haze (Somers and Ziemelis, 1985).

Pinking prevention in white wine
Pinking in white wine is caused by malvidin-3-O-glucosides located in the pulp and skin.25   For a literature review of pinking in white wine, read: Nel, Anton & du Toit, Wessel & van Jaarsveld, Francois. (2020). Pinking in White Wines - A Review. South African Journal for Enology and Viticulture. 41. 151. 10.21548/41-2-3952.  

Ultrafiltration 

• Pinking can be removed with membranes of ~500 Da and, if filters with lower cutoff values are used, they can produce blush or white wines from red or rosé wines. 
• Drawback: Ultrafiltration may remove important aroma compounds.

PVPP (polyvinylpolypyrrolidone) 

• Removes brown or pink pigments from white wines, especially those assiduously protected from oxidation during and subsequent to crushing, by binding tannins into large macromolecular complexes (Jackson, Wine Science). 
• Procedure: PVPP facilitates pigment removal by filtration or centrifugation. According to the technical specifications for Polycel (an IOC PVPP product): The mix should be added to 20 times its weight in cool water, allowed to sit for one hour before being added into the tank, then left to settle for up to a week before being racked or filtered out.
• Commercial example: Polycel by IOC, a mix of PVPP and micropulverized cellulose which can be purchased from Scott Labs (https://shop.scottlab.com/polycel-1kg-015784 ). 

Sulfur dioxide
Usage:  Analysis of SO2, pH and polyvinyl polypyrrolidone (PVPP) showed that a minimum of 45 mg/L of SO2 were needed for the wine not to be susceptible to pinking. [26]

Other color removal techniques
According to Jackson in Wine Science the following techniques can also be used to reduce phenolic content in wine.

• Using fining agents like gelatin, egg albumin, or the dairy product casein to create large protein–tannin complexes which can be settled, filtered or centrifuged out.
• Activated carbon may be used to remove color, however it can also remove aromatic compounds. 
• Premium-quality red wines often develop a tannin sediment due to precipitation. This potential source of haziness is typically not viewed as a fault but rather an indicator of not over refining the wine.

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Yeast Assimilable Nitrogen (YAN)

• Influence of YAN on Fermentation 
  
• Source and Quantity Required
• YAN Adjustment

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Influence of YAN on Fermentation 
Yeast requires various nitrogen compounds for sugar transport, the synthesis of proteins, pyrimidine nucleotides, and nucleic acids, especially during the log phase (when yeast rapidly divides); however, it must be in a usable/assimilable form factor.  Jackson noted the following in Wine Science:

Nitrogen content can influence the synthesis and release of aromatic compounds during fermentation. For example:

A reduction in fusel alcohol occurs in the presence of ammonia and urea. 

During, and especially after fermentation, nitrogen and other constituents are slowly released into the wine by yeast autolysis. This may activate subsequent microbial activity, the reason that the first racking typically occurs shortly after fermentation (Jackson, Wine science). Racking may be delayed if:

• If malolactic fermentation is desired, then bacterial conversion of malic to lactic acid is completed first.
• If extended lees contact (sur lie maturation) with the wine is desired. 
• Large molecular weight nitrogen-containing compounds like mannoproteins may also be released near the end of fermentation, especially during sur lie maturation. 

 

Source and Quantity Required [27]
YAN requirement can be sufficiently supplied by the grape’s solids, and varies by yeast strain, to the extent that Scott Labs includes general YAN requirements on their yeast sales sheets.  

• Excessive concentrations can promote unnecessary cell multiplication and reduce the conversion of sugar to alcohol (Jackson, Wine Science). 
• Deficiencies can cause slow fermentation or “stuck” fermentations, and enhance the release of higher alcohols and sulfide evolution.

Yeast YAN requirements from Scott Labs:

• Low nitrogen-demand:  Yeast need 7.5 ppm YAN per 1 °Brix
• Medium nitrogen-demand: Yeast need 9 ppm YAN per 1 °Brix
• High nitrogen-demand:  Yeast need 12.5 ppm YAN per 1 °Brix

YAN requirements are also influenced by:

Initial sugar content: The higher the initial sugar content, the more YAN required.
Temperature: An increase in temperature stimulates fermentation rate and yeast growth, thereby requiring increased levels of nitrogen.

Oxygen: When adding oxygen to the juice/must, nitrogen is captured faster, therefore more nitrogen is needed.
Turbidity: When juice is over-clarified (<50 NTU), many nutritional factors for yeast are removed, making it necessary to supplement with complete and balanced nutrients.

Pre-fermentation practices: As discussed in the March issue, (found at hawaiibevguide.com/wine-making-pre-permentation-process) epiphytic and spontaneously occurring non-saccharomyces yeast consume nitrogen, vitamins, minerals and other essential nutrients. Since this occurs before the primary fermenters of Saccharomyces cerevisiae start, the must may be deficient in these nutrients and require supplementation. Clarification, typical in the production of white wine, also makes the wine more susceptible to nitrogen deficiencies. 

Fruit quality (free from disease): The presence of molds or rot will reduce nitrogen content and other essential nutrients in juice/must. For example, juice nitrogen content may also be reduced by 33–80% in grapes infected by Botrytis cinerea. [28]

Wine style can also influence nitrogen requirements.  Jackson notes in Wine Science:

• Sparkling wine production: Nitrogen deficiency caused by the initial fermentation and clarification of the cuvée wines is usually counteracted by the addition of ammonium salts such as diammonium phosphate (DAP). 
• Some grape varieties like Chardonnay and Colombard are more susceptible to nitrogen deficiency, especially if excessive  pre-fermentative centrifugation or filtration occurs.
• Yeast extract may be added to favor malolactic fermentation. If used, it is usually done at the end of fermentation.
• Small cooperage and a larger surface area/volume ratio provides better contact between the wine and the lees and increased liberation of assimilable nitrogen into the wine.​

YAN Adjustment [30]
YAN requirement varies by yeast strain and can be sufficiently supplied by the grape’s solids. If there are deficiencies, they may be supplemented in winemaking by: 

• Organic nitrogen, in the form of amino acids and peptides, with autolyzed yeast being a common winemaking source.
• Nitrogen supplemented by amino acids have a lower increase in fermentation temperature compared to DAP supplied nitrogen. The yeast population is controlled, and the cells are healthier (Scott Lab).
• Inorganic nitrogen in the form of ammonia is typically obtained from the application of DAP and other ammonia salts.
• Though traditionally used (and the typical adjustment referenced in academic literature for YAN), DAP-supplied nitrogen has a very quick uptake, which can lead to uncontrolled cell growth and hot fermentations. It does not necessarily give yeast the staying power to complete a fermentation. Additionally, both aroma and mouthfeel are improved when DAP is avoided (Scott Lab).
• In comparison: While yeast may show an affinity for ammonia, a yeast diet balanced with amino acids can produce healthier fermentations, better aromatics (e.g. terpenes and esters) and lower levels of undesirable compounds (e.g. ethyl acetate and hydrogen sulfide).

Process: 

• DAP is added halfway through fermentation in multiple doses, because it favors the uptake of amino acids and benefits the synthesis of sugar transport proteins (Jackson, Wine Science).  Additional nutrients may be necessary, since the higher the YAN, the more vitamins and minerals yeast requires as they are co-factors for growth and aroma metabolism.
• Organic nitrogen like Fermaid O, a product of Scott Laboratories, is suspended in water and then added at the start of alcoholic fermentation. [31]

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Sulfur Dioxide [32]

The AWRI, in an article entitled “Revisiting Sulfur Dioxide”  has advocated a better understanding of its usage in wine because of the reluctance of winemakers to increase SO2 usage due to possible adverse reactions by consumers, or a perceived consumer demand for lower SO2 concentrations. Despite  the notion that large additions of SO2 to red wine can have a negative sensory effect, often negative effects such as the bleaching of color are transitory, and are far outweighed by the negative sensory effect of subsequent wine spoilage.

• Primary Usage
• Mechanism
• Quantity Needed
• Usage Proces

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Primary Usage
Sulfur dioxide’s primary usage is as an antimicrobial agent which suppresses growth of bacteria and non-Saccharomyces strains of yeast.  The degree to which it is suppressed depends on the species, strain, and fermentation conditions. Additionally: 

• Sulfur dioxide is more effective against bacterial flora, and, when combined with the low pH of grape juice, increases the proportion of its most effective anti-microbial form, molecular SO2 (Jackson, Wine Science).
• Has antioxidant properties.
• Reduces caftaric acid quinone, which is one of the primary oxidation products, and enhances the solubility of phenolic compounds.
• Where the early onset of malolactic fermentation is desired, the addition of sulfur dioxide should be avoided.
• In white wine: It is thought to inhibit the grape polyphenol oxidases (browning) in white musts, especially when added in conjunction with ascorbic acid. However, this may just delay browning until the wine has been bottled.  Problematically, though browning is generally undesired, it can be precipitated out of the wine prior to bottling, but once bottled, it cannot. Ascorbic acid added to white wine after crushing is generally not recommended.
• In red wine, anthocyanins can be bleached by sulfur dioxide. Though reversible, sulfur dioxide also binds to flavonoids and can delay or suppress the formation of protoanthocyanins like vitisins, which are color stabilizing complexes between anthocyanins and tannins.33
• Can impact yeast-derived flavors and impart a metallic taste to the wine.

Mechanism
SO2 reacts with different components present in the grape juice/must or wine to bind and become inactive as an antioxidant and antimicrobial agent. What remains is free SO2 in two parts: bisulfite (HSO3-) and molecular SO2, with the molecular SO2 being active against microorganisms and unwanted bacteria (Winebuisness.com).  In wineries, sulfur dioxide is measured as free, bound and total forms. These are [34]: 

Free sulfur dioxide: The unreactive components made up of mostly the molecular sulfur dioxide and bisulfite forms. This is the portion of the sulfur dioxide which has the important antioxidant and antimicrobial properties, therefore the most important measurement of SO2 concentration of a wine is the free SO2 concentration.
Bound sulfur dioxide: The proportion of the bisulfite formed which binds with other wine components such as pigments and phenolic.

Total sulfur dioxide: A total amount of sulfur dioxide added, or the sum of the free and bound fractions 
Molecular SO2: The recommended level of molecular SO2 for red wines is 0.5 mg/L (ppm); for white wines is 0.8 mg/L (ppm); and for dessert wines is up to 1.5 mg/L (ppm). Free SO2 over 50 mg/L (ppm) can be tasted and detected in the wine’s aroma.

Quantity Needed
According to AWRI:

Maximum legal limits of SO2 concentrations in Australian wines: 

• 250 mg/L for wines containing less than 35 g/L of residual sugar. 
• 300 mg/L for wine containing in excess of 35 g/L of residual sugar.

The quantity required depends on:

pH: As at higher pH levels (the must is less acidic), more SO2 is needed, not just because of the antimicrobial properties of the environment, but because of the reduced ability for free SO2 to be transformed into molecular SO2.

Temperature: Given the same amount of total SO2, a lower temperature wine will have  lower amounts of free SO2 than a wine held at a higher temperature.

Alcohol: Given the same amount of total SO2, a lower alcohol wine will have a lower free SO2 than a wine with higher alcohol.
Grape health. Grapes free from molds, mildew, and other diseases have fewer unwanted microbes, and the presence of microbial by-products such as glucuronic and galacturonic acids can reduce the antimicrobial influence of sulfur dioxide (Jackson, Wine Science).

Grape harvest practices: Careful picking minimizes bruising or incidental crushing, which can lead to unwanted microbial growth.

Fermentation practices: Temperature in particular suppresses unwanted microbial growth. 

Concentration of dissolved oxygen: This is critical to account for, as 1 mg/L of oxygen can consume 4 mg/L of SO2 and during the bottling process, a 0.5-1.5 mg/L increase is typical (Boulton et al. 1996).

Wine Style:

• Wines intended for early consumption require less SO2 than those intended for medium to long term storage.
• The final storage container also matters, as wines sold in bladder packs intended for early consumption may also lose SO2 through the packing, due to the oxygen permeability of the bladder material.
• Wine haziness can bind up a large proportion of the free SO2. To prevent this scenario and achieve the highest possible concentration of free SO2 at bottling, a high degree of clarity throughout the maturation period is ideal, or the use of filtration or centrifugation of hazy wine before bottling.

Cultivar: 
​Cultivars may have a “critical” level of free SO2 concentration, in which lower amounts will generally be deemed to taste or look more deteriorated through oxidation and/or browning. For example: 

• AWRI’s closure trial (AWRI publication #666) found Semillon wines with free SO2 below ~10 mg/L were rated high in the attribute oxidized, whereas samples with above ~10 mg/L SO2 were rated considerably lower in the attribute. 
• Godden (Technical Review #139) found that browning and deterioration of the Semillon wine’s sensorial attributes accelerated when free SO2 fell below the ~10 mg/L (the wine in this study had a pH of 3.1). 
• Given that pH influences the free SO2 concentration in wine, those with higher pH values than Semillon should have higher critical levels. This was corroborated by a closure trial study of multiple bottles of Chardonnay with a pH of 3.57, which suggest that the critical free SO2 concentration below which browning and sensorial deterioration of the wine accelerated, was approximately 15 mg/L. 

Usage Process
If added, sulfur dioxide is applied several hours before yeast inoculation, usually at crushing, at a dosage of 50–100 mg/liter, depending on the health of the fruit and the maceration temperature. The AWRI in “Revising Sulfur Dioxide Usage” recommends that larger additions are preferable to multiple smaller additions of equivalent SO2 inorder for the concentration of free SO2 to reach a level where it has a substantive antioxidant or anti-microbial impact ( the alternative is a high percentage of bound SO2).

It can come in the following forms [35]: 

SO2 addition as liquid solution (H2SO3) 
Prepared by bubbling gaseous SO2 into water and adding that solution to the grape must. 

SO2 addition as potassium metabisulfite (K2S2O5) 
A white crystalline salt which contains 57.6 % SO2, potassium metabisulfite is dissolved into warm water before being applied to the juice/must. This reacts with natural acids to release sulfur dioxide.

SO2 reduction by hydrogen peroxide (H2O2) 
H2O2 is slowly added to the wine in a diluted form to avoid oxidation, then rested for several hours, which allows it to reach an equilibrium state. At this point, an analysis is conducted to determine if additional H2O2 is needed.

Potential Disadvantages of SO2
Jackson notes in Wine Science, disadvantages include:

• Slowing the onset of fermentation. The presence of 15–20 ppm can reduce the viability of a yeast inoculum, however, the typically used concentration on healthy grapes of less than 50 ppm of total free SO2 does not appear to affect the rate of alcoholic fermentation. 
• Can significantly influence yeast metabolism by readily binding with several carbonyl compounds, notably acetaldehyde, pyruvic acid, and α-ketoglutaric acid. This increases their biosynthesis and potential release into the fermenting must, and their concentration in the finished wine often correlates with the concentration of sulfur dioxide added to the must (Jackson, Wine Science).
• Has control over many, but not all, spoilage yeasts. Many strains of Saccharomycodes ludwigii, Zygosaccharomyces bailii, and Brettanomyces spp. are particularly tolerant to sulfur dioxide. 

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Enzyme Addition [36]

Enological enzymes may be added at various points in the winemaking process to accelerate or enhance the clarification, extraction, filtration, and stability of grape must, as well as influence microbial activity.   They primarily work by breaking bonds between large molecules. In “Use of Enzymes in Juice and Wine Production” by the Grape Chemistry Group at Virginia Tech. ​

Notable enological enzymes

• Glucanases
• β-Glucosidases
  
• Cinnamoyl esteras
• Pectinase
• Lysozymes
• Anthocyanases ​

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​Glucanases, especially Β-glucanases 
Can be used:
To help clarify and filter juice from Botrytis-infected grapes, as these often have elevated β-glucan levels, which cause significant problems in clarification and filtration.
During sur lie maturation, to potentially enhance the release of mannoproteins associated with the yeast cell capsule and enhance suppleness.
In distilling and brewing, it also can be used to break down β-glucans present in rye, barley, wheat, and other cereals, resulting in reduced viscosity, which makes pumping easier after mashing.
Produced from: β-glucanase from Trichoderma harzianum
Commercial examples include:  
Lallemand’s Lallzyme MMX 
shop.scottlab.com/lallzyme-mmx-100g-016207
Laffort Exralyse: 
laffort.com/en/products/extralyse

β-Glucosidases 
Can be used to cleave bonds of glycosidically-bound aroma/flavor precursors to unlock the aroma-producing compound of high-terpene white grapes, including Riesling, Gewürztraminer, and Muscat. In brewing, it can be similarly used to improve hop aroma.

Produced from: Pectolytic enzymes as many have some β-glucosidase activity.
Commercial examples include: 
Scottzyme® BG (used post-fermentation) is a combination of pectinase and β-glucosidases for the release of bound terpenes. shop.scottlab.com/scottzyme-bg-1kg-016176 
Laffort Lafazym Arom: laffort.com/en/products/lafazym-arom/?gamme=2447 ​

Cinnamoyl esterase
Used to: Unbind aroma compounds like thiols from their precursors.

Drawback: Some Aspergillus niger enzyme preparations crate a phenolic off-odor (Jackson, Wine Science). 
Commercial example: 
Oneolabs Rapidase (https://shop.scottlab.com/rapidase-expression-aroma-100g-016260)

Pectinase
Used to: Break down pectins, which increases yield, clarification rate, filterability, stability, and aroma enhancement, and aids in color extraction.

Drawbacks: Some pectinase preparations may cause the synthesis of excessive levels of vinylphenols, or clarification problems due to a production of fine particulate material derived from grape skins (Jackson, Wine Science).

Derived from filamentous fungi, notably Aspergillus and Trichoderma spp.

Commercial examples include:
Laffort Lafazym Thiols (Thiol enhancer): laffort.com/en/products/lafazym-thiols/?gamme=2447 
Laffort Lafase XL Clarification: laffort.com/en/products/lafase-xl-clarification/?gamme=2447

Lysozymes
Used to: Prevent or delay malolactic fermentation by controlling gram-positive lactic acid bacteria.
Produced from:  Egg whites.
Drawbacks:
As a protein, lysozyme is reactive with phenolics in red wines, where it can potentially create instability. This results in a perceptible reduction in wine tannins and color. Bartowsky et al. (2004) noted a 17% reduction in 520 nm absorbance (red wine anthocyanin absorption maximum) for Cabernet Sauvignon and Shiraz.
In white wines, lysozyme may contribute to protein instability, which is not easily corrected by bentonite.
Bentonite will bind with a portion of the lysozyme added, and may reduce its concentration below that which is needed for bacterial control.
Commercial Example:
DelvoZyme: shop.scottlab.com/%23/5kg-delvozyme-lysozyme-016404 

For more about grape enzyme usage read: 
Grape Chemistry Group at Virginia Tech. (n.d.). Use of Enzymes in Juice and Wine Production. Wine / Enology Grape Chemistry Group. Retrieved April 21, 2022, from www.apps.fst.vt.edu/extension/enology/downloads/wm_issues/Enzymes%20In%20Winemaking.pdf

Anthocyanases represent a group of fungal-derived enzymes that may also be present as contaminants in enzyme formulations. Anthocyanins are covalently linked with glucose. Hydrolysis of the glucose from the pigment molecule leads to destabilization, and, subsequently, diminished color.

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Other Yeast Nutrients

• Vitamins and minerals
• Lipids

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Vitamins and minerals
Typically available in sufficient amounts in grape must, they are needed by yeast for various metabolic functions. Jackson in Wine Science provided the following example:

• Vitamins influence yeast metabolism, and are used by yeast as coenzymes and enzyme precursors. Though typically available in sufficient amounts in grape juice or through biosynthesis, if a situation significantly reduces their concentration and results in a stuck fermentation, vitamin addition is required. 
• Minerals like potassium and magnesium are the active (catalytic) sites of enzymes, used to regulate cellular metabolism and help maintain cytoplasmic pH and ionic balance. These are typically in adequate supply in grape juice. 

Lipids
Lipids, the primary component of cell membranes (lipid bilayer), is essential for yeast development. In inoculated fermentation under aerobic conditions, adequate precursors from the grape solids are typically sufficient for yeast to synthesize their own lipids. According to Jackson in Wine Science, lipid deficiencies causing slow or stuck fermentations may result from: 

• Excessively clarified juice.
• Usage of spontaneous fermentation instead of inoculation; 16 or more cell divisions are required to create a significant enough yeast population for fermentation, therefore more lipids are required.  
• Yeast metabolic byproducts of saturated fatty acids, including octanoic and decanoic acid, can be toxic to wine yeast. Their toxicity increases with a decrease in pH, and can be limited or negated by the addition of ergosterol and long chain unsaturated fatty acids, or with absorptive products like activated charcoal, bentonite, silica gel, or yeast hulls (consisting primarily of cell-wall remnants following controlled autolysis).

Lipid Modification
If additional sterols and/or unsaturated fatty acids are needed, yeast hulls or yeasts with high sterol content may supplement sterol content, because musts inoculated with strains possessing enhanced sterol contents frequently ferment more sugar than strains possessing low sterol contents.

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​Other Factors Influencing Fermentation

• Fermentation duration
  
• Pesticide usage
• Grape Health

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Fermentation duration
Especially significant if skin contact occurs, as the longer fermentation takes, the more contact there is.  However, maceration and other techniques can influence the duration of skin contact beyond that of fermentation.




Grape health
Botrytized grapes
Botrytis grows in cool, wet, environments.  

Botrytis can negatively impact wine by: 
Producing an oxidative enzyme called laccase which in the presence of oxygen can cause oxidative spoilage and rapid browning of must.  Casse usually develops early during maturation and precipitates before bottling, it does not cause in-bottle clouding (Jackson, Wine Science).
Oxidize glucose to produce gluconic acid which at elevated levels can contribute to a sour taste in musts or wine.
A high sugar content.
Result in the formation of polysaccharides, β-glucans in particular, that can create clarification problems in juice and filtration problems in wine.
Lead to the presence of a moldy character in wine.

Mitigation strategies include
Exclusion of botrytis infected berries through sorting practices.
Heat treatment to denature the lacasse.
Usage of glucanases, especially Β-glucanases.  See Section on Enzyme addition for more information.

For more on the impact of botrytis on wine and its management in winemaking read:

The Australian Wine Research Institute. (n.d.). Botrytis. The Australian Wine Research Institute. Retrieved April 22, 2022, from http://www.awri.com.au/industry_support/viticulture/pests-and-diseases/botrytis/ 

Pesticide usage
Fungicides, Insecticides, herbicides can negatively impact fermentation, and flavor. For example, Conner (1983) studied the impact of fungicides, insecticides, and herbicides on yeast during wine fermentation and found37:

Fungicides: 
Very toxic to yeast: Dinocap was the most potent, with captan, mancozeb and maneb also being very toxic. 
Less toxic to yeast: Benomyl, copper oxychloride, iprodione, procymidone, triadimefon, triforine, vinclozolin and zineb. 
Non-toxic to yeast: Copper sulfate and sulfur.  Jackson notes in Wine Science that newer fungicides, including metalaxyl (Ridomil®) and cymoxanil (Curzate®), do not appear to affect fermentation

Insecticide: 
Particularly toxic to yeast; Dicofol
Non toxic to yeast: dieldrin, lindane, maldison, methiocarb, mevinphos and rotenone

Herbicides 
Slightly Toxic: diuron and 2,2-dichloropropionic acid
Non-toxic to yeast: 2,4-dichlorophenoxyacetic acid and simazine

For more on pesticides usage and its influence on wine production read:
Caboni, Pierluigi & Cabras, Paolo. (2010). Chapter 2 - Pesticides' Influence on Wine Fermentation. Advances in Food and Nutrition Research. 59. 43-62. 10.1016/S1043-4526(10)59002-8.  Retrieved from: www.researchgate.net/publication/223598587_Chapter_2_-_Pesticides%27_Influence_on_Wine_Fermentation 

Grape health

Botrytized grapes
Botrytis grows in cool, wet, environments.  

Botrytis can negatively impact wine by: 

• Producing an oxidative enzyme called laccase which in the presence of oxygen can cause oxidative spoilage and rapid browning of must.  Casse usually develops early during maturation and precipitates before bottling, it does not cause in-bottle clouding (Jackson, Wine Science).
• Oxidize glucose to produce gluconic acid which at elevated levels can contribute to a sour taste in musts or wine.
• A high sugar content.
• Result in the formation of polysaccharides, β-glucans in particular, that can create clarification problems in juice and filtration problems in wine.
• Lead to the presence of a moldy character in wine.

Mitigation strategies include:

• Exclusion of botrytis infected berries through sorting practices.
• Heat treatment to denature the lacasse.
• Usage of glucanases, especially Β-glucanases.  See Section on Enzyme addition for more information.

For more on the impact of botrytis on wine and its management in winemaking
The Australian Wine Research Institute. (n.d.). Botrytis. The Australian Wine Research Institute. Retrieved April 22, 2022, from http://www.awri.com.au/industry_support/viticulture/pests-and-diseases/botrytis/

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Resources and Suggested Reading

1.  Legal Information Institute. (n.d.). 27 CFR § 24.246 - materials authorized for the treatment of wine and juice. Legal Information Institute. Retrieved April 20, 2022, from https://www.law.cornell.edu/cfr/text/27/24.246 
   
   
2. Erasmus, D. J., Cliff, M., & Van Vuuren, H. J. (2004). Impact of yeast strain on the production of acetic acid, glycerol, and the sensory attributes of icewine. American Journal of Enology and Viticulture, 55(4), 371-378. www.researchgate.net/publication/270274181_Sensory_profiles_of_ice_wines_fermented_with_different_yeast_strains
   
   
3. Duitschaever, C. L., Alba, J., Buteau, C., & Allen, B. (1991). Riesling wines made from must concentrated by reverse osmosis. I. Experimental conditions and composition of musts and wines. American journal of enology and viticulture, 42(1), 19-25. https://www.ajevonline.org/content/42/1/19.short 
   
   
4. Mietton-Peuchot, M., Milisic, V., & Noilet, P. (2002). Grape must concentration by using reverse osmosis. Comparison with chaptalization. Desalination, 148(1-3), 125-129. Source: https://www.academia.edu/27128208/Grape_must_concentration_by_using_reverse_osmosis._Comparison_with_chaptalization 
   
   
5. Guyon, F., Douet, C., Colas, S., Salagoïty, M. H., & Medina, B. (2006). Effects of must concentration techniques on wine isotopic parameters. Journal of agricultural and food chemistry, 54(26), 9918-9923.  https://www.academia.edu/download/76005757/jf062095f20211209-26470-ncbu68.pdf 
   
   
6.  Varela, C. (2016, June 30). Factors affecting wine texture, taste, clarity, stability and production efficiency. Wine Australia. Retrieved April 20, 2022, from https://www.wineaustralia.com/research/search/completed-projects/awri-3-1-4 
   
   
7. Malherbe, D. F. (2010). Characterization and evaluation of glucose oxidase activity in recombinant Saccharomyces cerevisiae strains (Doctoral dissertation, Stellenbosch: Stellenbosch University) http://scholar.sun.ac.za/handle/10019.1/4008 
   
   
8. Swiegers, Jan & Bartowsky, Eveline & Henschke, P.A. & Pretorius, Isak. (2005). Yeast and bacterial modulation of wine aroma and flavour. Australian Journal of Grape and Wine Research. 11. 139-173. Retrieved from: www.researchgate.net/publication/280765129_Yeast_and_bacterial_modulation_of_wine_aroma_and_flavour 
   
   
9. Harbertson, J., & Henick-Kling, T. (2010, October 13). Managing High Acidity in Grape Must and Wine | WSU Viticulture and Enology | Washington State University. Washington State University Viticulture and Enology. Retrieved April 21, 2022, from wine.wsu.edu/2010/10/13/managing-high-acidity/
   
   
10. Scollary, G., & Fahey, D. (2020). Acidity Management of Grapevines and Wines. New South Wales Government - Department of Trade & Investment. https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0007/1265227/Acidity-management-of-grapevines-and-wines.pdf 
    
    
11. Potassium hydrogen tartrate. ECHA. (n.d.). Retrieved April 20, 2022, from https://echa.europa.eu/registration-dossier/-/registered-dossier/11349/4/22 
    
    
12. National Center for Biotechnology Information (2022). PubChem Compound Summary for CID 525, Malic acid. Retrieved April 4, 2022 from https://pubchem.ncbi.nlm.nih.gov/compound/Malic-acid.
    
    
13. UC Davis Department of Viticulture and Enology. (2018, April 3). Citric Acid. UC Davis Viticulture and Enology. Retrieved April 22, 2022, from https://wineserver.ucdavis.edu/industry-info/enology/methods-and-techniques/common-chemical-reagents/citric-acid
    
    
14. National Center for Biotechnology Information (2022). PubChem Compound Summary for CID 612, Lactic acid. Retrieved April 4, 2022 from https://pubchem.ncbi.nlm.nih.gov/compound/Lactic-acid.
    
    
15. National Center for Biotechnology Information (2022). PubChem Compound Summary for CID 612, Lactic acid. Retrieved April 4, 2022 from https://pubchem.ncbi.nlm.nih.gov/compound/Lactic-acid.
    
    
16. National Center for Biotechnology Information (2022). PubChem Compound Summary for CID 176, Acetic acid. Retrieved April 4, 2022 from https://pubchem.ncbi.nlm.nih.gov/compound/Acetic-acid.
    
    
17. National Center for Biotechnology Information (2022). PubChem Compound Summary for CID 1110, Succinic acid. Retrieved April 4, 2022 from https://pubchem.ncbi.nlm.nih.gov/compound/Succinic-acid.
    
    
18. Australian Wine Research Institute. (n.d.). Acidity and pH. The Australian Wine Research Institute. Retrieved April 21, 2022, from www.awri.com.au/industry_support/winemaking_resources/frequently_asked_questions/acidity_and_ph/ 
    
    
19. Haggerty, Luke LeMay. (2013). Ripening profile of grape berry acids and sugars in University of Minnesota wine grape cultivars, select vitis vinifera, and other hybrid cultivars. Retrieved from the University of Minnesota Digital Conservancy. https://conservancy.umn.edu/handle/11299/160115  
20. Steiner, T. E. (2020). Acid management of must and wine - Ohio State University. Ohio State University . Retrieved April 20, 2022, retrieved from https://ohiograpeweb.cfaes.ohio-state.edu/wine-making/pre-fermentation-practices 
    
    
21. Deacidification. The Australian Wine Research Institute. (2021, April 14). Retrieved April 20, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/frequently_asked_questions/deacidification/ 
    ​
22. Cole, J., and R. Boulton. "A study of calcium salt precipitation in solutions of malic and tartaric acid." VITIS-Journal of Grapevine Research 28, no. 4 (2015): 177. https://ojs.openagrar.de/index.php/VITIS/article/view/5868 
    
    
23. ​
24. Bonorden, W. R., Nagel, C. W., & Powers, J. R. (1986). The adjustment of high pH/high titratable acidity wines by ion exchange. American journal of enology and viticulture, 37(2), 143-148.
    https://www.ajevonline.org/content/37/2/143.short 
    
    
25. Chatonnet, P., Dubourdieu, D., & Boidron, J.-N. (1989). Incidence de certains facteurs sur la décarboxylation des acides phénols par la levure. OENO One, 23(1), 59–62. https://doi.org/10.20870/oeno-one.1989.23.1.1728
    
    
26. Cosme, F., Andrea-Silva, J., Filipe-Ribeiro, L., Moreira, A. S. P., Malheiro, A. C., Coimbra, M. A., ... & Nunes, F. M. (2019). The origin of pinking phenomena in white wines: An update. In BIO Web of Conferences (Vol. 12, p. 02013). EDP Sciences. bio-conferences.org/articles/bioconf/pdf/2019/01/bioconf-oiv2018_02013.pdf 
    
    
27. Magyar, Ildikó. (2011). Botrytized Wines. Advances in food and nutrition research. 63. 147-206. 10.1016/B978-0-12-384927-4.00006-3.  https://www.researchgate.net/publication/51596128_Botrytized_Wines 
    
    
28. Yeast assimilable nitrogen article. The Australian Wine Research Institute. (2012, January 13). Retrieved April 20, 2022, from https://www.awri.com.au/commercial_services/analytical_services/analyses/yeast_assimilable_nitrogen/yeast-assimilable-nitrogen-3
    
    
29. Yeast Nutrition: Amino Acids Are Better Than Ammonia (DAP). (2021, September). Retrieved April 21, 2022, from https://scottlab.com/yeast-nutrition-inorganic-vs-organic-nitrogen 
    
    
30. Product details. Lallemand Œnology. (n.d.). Retrieved April 20, 2022, from https://www.lallemandwine.com/en/china/products/catalogue/nutrients-protectors/1/fermaid-o/ 
    
    
31. Revisiting sulfur dioxide use. The Australian Wine Research Institute. (2011, June 13). Retrieved April 20, 2022, from www.awri.com.au/industry_support/winemaking_resources/fining-stabilities/microbiological/avoidance/sulfur_dioxide/ 
    
    
32. Morata et al., 2006  Effects of pH, temperature and SO2 on the formation of protoanthocyanins during red wine fermentation. /www.academia.edu/download/48028957/Effects_of_pH_temperature_and_SO2_on_the20160813-21033-lx2cc.pdf 
    
    
33. Understanding molecular SO - Australian Wine Research Institute. (2017, January). Retrieved April 21, 2022, from https://www.awri.com.au/wp-content/uploads/2018/03/s1886.pdf 
    
    
34. So2 addition as liquid solution (H2SO3). Wine Business. (n.d.). Retrieved April 20, 2022, from https://www.winebusiness.com/calculator/winemaking/calc/1/
    
    
35. Grape Chemistry Group at Virginia Tech. (n.d.). Use of Enzymes in Juice and Wine Production. Wine / Enology Grape Chemistry Group. Retrieved April 21, 2022, from www.apps.fst.vt.edu/extension/enology/downloads/wm_issues/Enzymes%20In%20Winemaking.pdf 
    
    
36. Conner, A. J. (1983). The comparative toxicity of vineyard pesticides to wine yeasts. American Journal of Enology and Viticulture, 34(4), 278-279. https://www.ajevonline.org/content/34/4/278
    
    
37. Australian Wine Research Institute. (n.d.). Managing Botrytis-infected fruit, must and wine. The Australian Wine Research Institute. Retrieved April 22, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/climate-wine-production/managing-botrytis/
    
    
38. Bindon, K., Petrie, P.(2020). Quantifying the advancement and compression of vintage.https://www.wineaustralia.com/getmedia/e5c30d7b-4e14-476a-844a-0037342b3165/20200921-AWR-1701-4-1-1-Final-Report.pdf 
    
    
39. Schelezki, O.J.; Antalick, G.; Šuklje, K.; Jeffery, D.W. Pre-Fermentation Approaches to Producing Lower Alcohol Wines from Cabernet Sauvignon and Shiraz: Implications for Wine Quality Based on Chemical and Sensory Analysis. Food Chem. 2019, 309, 125698. https://digital.library.adelaide.edu.au/dspace/bitstream/2440/117802/2/Schelezki2018_PhD.pdf#page=107
    
    
40. Teng, B.; Petrie, P.R.; Nandorfy, D.E.; Smith, P.; Bindon, K. Pre-Fermentation Water Addition to High-Sugar Shiraz Must: Effects on Wine Composition and Sensory Properties. Foods 2020, 9, 1193. https://doi.org/10.3390/foods9091193
    
    
41. Piccardo, D., Gombau, J., Pascual, O., Vignault, A., Pons, P., Canals, J.M., González-Neves, G. and Zamora, F., 2019. Influence of two prefermentative treatments to reduce the ethanol content and pH of red wines obtained from overripe grapes. Vitis, 58(5), pp.59-67. https://doi.org/10.5073/vitis.2019.58.special-issue.59-67
    
    
42. Schelezki, O.J.; Deloire, A.; Jeffery, D.W. Substitution or Dilution? Assessing Pre-Fermentative Water Implementation to Produce Lower Alcohol Shiraz Wines. Molecules 2020, 25, 2245. https://doi.org/10.3390/molecules25092245 
    
    
43. Pickering, G. The Production of Reduced-Alcohol Wine Using Glucose Oxidase. Ph.D. Thesis, Lincoln University, Lincoln, UK, 1997. https://researcharchive.lincoln.ac.nz/handle/10182/1979 
    
    
44. Biyela, B.N.E.; du Toit, W.J.; Divol, B.; Malherbe, D.F.; van Rensburg, P. The Production of Reduced-Alcohol Wines Using Gluzyme Mono® 10.000 BG-Treated Grape Juice. South African J. Enol. Vitic. 2009, 30, 124–132. http://scholar.sun.ac.za/handle/10019.1/8422 
    
    
45. Botezatu A, Elizondo C, Bajec M, Miller R. Enzymatic Management of pH in White Wines. Molecules. 2021; 26(9):2730. https://doi.org/10.3390/molecules26092730
    
    
46. Salgado, C. M. (2016). Tesis Doctoral: Optimization of nanofiltration membrane processes applied to grape must for the production of low alcohol wines. Retrieved from: https://uvadoc.uva.es/handle/10324/17457