​Malolactic Fermentation

​​​Malolactic Fermentation (MLF) is the conversion of malic acid into lactic acid in order to lower acidity (increase in pH) and increase mouthfeel via lactic acid bacteria (LAB). While most pronounced in buttery chardonnay, often called cougar juice, it is most common in red wine fermentations of any sort.

• Influence on Wine
• Mechanisms of Reaction
• Process

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Benefits to MLF
Reduces Acidity

Increases pH and lowers
Titratable Acidity (TA)
According to Jackson in Wine Science, each gram per liter (g/L) of malic acid theoretically contributes 1.12 g/L to the titratable acidity (TA) expressed in terms of tartaric acid. If all of the malic acid is converted to lactic acid, the TA will drop by 0.56 g/L for each g/L of malic acid that was originally present in the wine. For example, if a wine starts with 2 g/L of malic acid, the TA would be expected to drop by 1.12 g/L after MLF.

Degrades other organic acids
Jackson notes in Wine Science:

• Citric acid is oxidized and correlated with the synthesis of acetic acid and diacetyl.
• Gluconic acid, which is often found in botrytized wines, is also metabolized by lactic acid bacteria.
• The degradation of tartaric acid by lactic acid bacteria is a wine fault called tourne.
• Sorbic acid is metabolized by lactic acid bacteria and forms 2-ethoxyhexa-3,4-diene (strong geranium-like odor).
• Some of yeast’s fatty acid metabolites, like decanoic and octanoic acids are toxic to lactic acid bacteria.

Produces desirable aroma compounds through the metabolism of citric acid
These aroma compounds include1:

• Diacetyl (2,3-butanedione), has a buttery, nutty aroma.2
• Acetoin (Butter, cream aromas)
• Ethyl lactate (Butter, cream, fruit aromas)
• Acetic acid (Vinegar aroma)
• Releases sugar-bound aromas through glycosidase activity.3

Can increase concentrations of higher alcohols fatty acid esters, and total esters.
For example, in red wine, Malherbe et al (2012) found4:

• A larger increase in ethyl esters than in acetate esters, in particular ethyl lactate, diethyl succinate (, ethyl octanoate, ethyl 2-methylpropanoate, and ethyl propionate.
• Hexyl acetate, isoamyl acetate, 2-phenylethyl acetate, and ethyl acetate were reduced or remained unchanged, depending on the strain and cultivar evaluated.
• Formation of ethyl butyrate, ethyl propionate, ethyl 2-methylbutyrate2-methylbutryate, and ethyl isovalerate was related to specific bacterial strains used, indicating possible differences in esterase activity.

Can reduce undesirable aroma compounds. Jackson notes in Wine Science:

• Compounds responsible for excessively vegetative, grassy aromas through the metabolization by lactic acid bacteria.
• Arginine, which has a bitter, musty taste, can be metabolized by lactic acid bacteria.

Drawbacks to MLF
The metabolism of carbonyl compounds (notably acetaldehyde) by lactic acid bacteria and the accompanying release of SO2 may result in some pigment bleaching. However, color loss associated with malolactic fermentation is significant only in pale-colored wines or those with an initially high pH (not acidic enough).
​
Potential Reduction in Microbial Stability

• Though it is thought to have a stabilizing effect on the wine, Jackson notes in Wine Science that the stabilizing effect is more likely due to associated practice like adequate usage of sulfur dioxide, storage at cool temperatures, and clarification applied after completion of malolactic fermentation. This protects the wine from acetic acid bacteria, spoilage lactic acid bacteria, and spoilage yeasts (notably Brettanomyces/Dekkera spp.
• As malolactic fermentation increases pH, this may cause microbial instability. Spoilage lactic acid bacteria increases rapidly as the pH rises above 3.5.

Organoleptic Defects Caused By Uncontrolled Malolactic Fermentation 5
Ropiness (oily wine) caused by production of the polysaccharides glucan or dextran from glucose is more common in white wines, and very rare in reds, because the causative organisms do not grow well in the presence of tannin.

Volatile phenols of 4-ethylphenol, 4-ethylgaiacol and 4-ethylcatechol, which have a barnyard-like aroma, are produced by Brettanomyces bruxellensis if it grows in wine during maceration or while waiting to undergo MLF. This is a major threat to wine quality, even under conditions of high alcohol, high SO2 and limited nutrient availability.

Biogenic amine development caused by lactic acid bacteria growth in high wine pH can lead to putrecine and cadaverine, which have putrefaction, meaty, vinegary and dirty aromas.

Mousiness (aroma) caused by heterofermentative lactobacillus, Oenococcus oeni and Brettanomyces and Dekkera yeast in high pH oxidative conditions, which creates pyridines.

The Mechanisms 6
Lactic acid bacteria are generally separated into two classes, which are defined by their metabolic process. These are:

Homofermentation: Embden-Meyerhof-Parnas (EMP) glycolytic pathway converts two moles of lactic acid and two moles of adenosine triphosphate (ATP) from each mole of glucose fermented.

​Heterofermentation: Hexose sugars like glucose are fermented to lactic acid, carbon dioxide, ethanol or acetic acid with a energy gain of one mole of ATP.

The enzymatic conversion of L-malic acid to L-lactic acid and CO2 by lactic acid bacteria
(LAB) occurs by:

• Malic acid is decarboxylated to pyruvic acid (which remains bound to the enzyme). This requires NAD and Mn+2 as co-factors. Pyruvic acid is then reduced to lactic acid, and ATP is generated.
• A minor (<1%), activity of the malolactic enzyme, which may stimulate stimulate LAB’s initial stages of glucose metabolism and initial growth rates through the provision of hydrogen acceptors (Kunkee 1991, and Boulton et al. 1998) by producing very small amounts of pyruvic acid and NADH2.

​Lactic Acid Bacteria
Lactic acid bacteria are adapted to grow in acidic environments and are one of the few groups of bacteria that can grow below a pH of 5. However, in the typical acidic conditions of must and wine, growth is restricted.

Oenococcus oeni

• Type of fermentation: heterofermentative It is the only species inducing malolactic fermentation in wines at a pH of 3.5
• pH
  • pH limit: 3.0–2.9
  • Optimum growth pH: 4.5–5.5

Differences between strains:
Scott Labs’ guide to “Choosing ML Bacteria and Nutrients” chart lists the following criteria differences: alcohol tolerance, pH Limit, total SO2 limit, temperature, relative nutrient demand, fermentation kinetics, compatibility with red/white/rosé and fruit wine, compatibility with yeast inoculation, assist with oak integration, diacetyl production, enhances freshness, enhances fruitiness, enhances mouthfeel and fullness, enhances spiciness, enhances
structure, minimizes herbaceousness

​Spoilage forms of lactic acid bacteria
Lactobacillus

• Type of fermentation: Lactobacillus contains both homo- and heterofermentative members.
• pH limit: below pH of 3.5.

Pediococcus

• Type of fermentation: Pediococcus is strictly homofermentative.
• pH limit: below pH 3.5.​

The process
Malolactic fermentation is induced through the creation of an “ideal” environment, then inoculation with the malolactic bacteria Oenococcus oeni.

Origin of Lactic Acid Bacteria
(Jackson, Wine Science)

• Infrequently isolated from grape or leaf surfaces in low numbers, it has no known habitat other than wine.

• ​Strains may originate from winery equipment like stemmers, crushers, ​presses, and fermentors, though the relative importance of grape versus winery sources has yet to be established.
• Often inoculated with commercial strains when malolactic fermentation is desired.

​The Ideal Environment [7,8]

Temperature: 18 – 22 °C is Favorable
Jackson in Wine Science notes:

• Traditionally, malolactic fermentation took place in the spring when cellars began to warm.
• ​The malic acid decarboxylation rate is primarily influenced by temperature where maximal decarboxylation is 20-25 °C and it stops at: below 10 °C

​Alcohol Level: <13% ABV is favorable
Ethanol retards bacterial growth, with different species varying in tolerance. Jackson notes in Wine Science:

• Lactobacillus spp. are the most ethanol-tolerant. L. trichodes can grow in wines at up to 20% ethanol.
• A few strains of Oenococcus oeni can grow in culture media at up to 15% alcohol.
• Alcohol tolerance appears to decline, both with increasing temperature and decreasing pH values. However, at low concentrations (1.5%), ethanol appears to favor bacterial growth.

pH: Favorable: 3.3 – 3.5 is favorable.

• Higher is good when SO2 concentrations are high.
• For wines marginally high in pH, tartaric acid may be added prior to the induction of malolactic fermentation (Jackson, Wine Science).

SO2: Favorable <30 mg/L.
Sulfur dioxide can inhibit malolactic fermentation, though the amount varies since
different factors influence the amount of
free SO2. For more about these factors, see
the section on Sulfur Dioxide. Additionally,
there is considerable variation between
species and strains, with Oenococcus oeni
being particularly sensitive.

Volatile acidity
Wines may have elevated VA due to high
pH, which allows other strains of bacteria
to grow. The wine should be monitored for
unwanted bacteria.

Yeast strains can inhibit lactic acid bacteria
growth to varying degrees, depending
on species and strain. Through research,
compatible strains have been found. Scott
Labs, in their 2021 Winemaking Handbook,
have indicated which yeast are more compatible in this regard. The mechanisms
that inhibit growth may include the increasing
ethanol content, the accumulation of carboxylic acids (notably octanoic and decanoic acid) and the production of proteins with antibacterial activities like lysozyme.

Oxygen in small amounts can favor malolactic fermentation by maintaining a
favorable redox balance through reaction
with flavoproteins.

Required Nutrients10

Carbohydrates
Sugars, primary hexoses (sugars with six
carbon atoms) of glucose and fructose,
are the primary source of energy for LAB,
with Oenococcus oeni being preferential
to fructose. Though glucose and fructose
concentrations are low at the end of fermentation, they, along with other usable
sugars, including monosaccharides of
arabinose, mannose, galactose and xylose,
as well as polysaccharides and glycosylated
compounds, are typically sufficient for
the LAB that is inoculated into the wine.
Additionally, glycosides where the aglycone
is bonded to glucose and a second
sugar molecule can be released by Oenococcus oeni-produced glycosidase enzyme activity.​

Organic Acids

• Malic and Lactic Acid: Wine conditions are difficult for bacteria if the malic level is <0.5 g/L or >7.0 g/L. The higher the malic acid levels, the higher the resulting lactic acid levels. This can be stressful for bacteria. Lactic acid levels of 1.5 g/L slow down bacteria, and 3 g/L starts to inhibit MLF.11
• Citric acid present in wine at a quantity between 0.1 – 0.7 g/L is a source of energy, and results in the formation of acetic acid, lipids, acetoin, butanediol and diacetyl.
• The higher the relative concentration of tartaric acid in the juice, the less likely malolactic fermentation will significantly affect the acidity and pH of the wine (Jackson, Wine Science).

Nitrogen
Amino acids and peptides must be supplied by the wine matrix, or be synthesized by the metabolism of wine LAB from organic sources, as wine bacteria cannot synthesize them from inorganic nitrogen.
Commercial nutrients available include:

• Lallemand Opti’Malo Plus®, a blend of inactive yeasts rich in amino acids, mineral cofactors, vitamins, cell wall polysaccharides and cellulose (which provides surface area to help keep the bacteria in suspension and to help adsorb toxic compounds that may be present at the end of primary fermentation). https://shop.scottlab.com/opti-malo-plus-1-kg-015141
• Lallemand Opti'MALO Blanc is a blend of selected inactivated yeasts, which helps compensate for amino nitrogen and peptide deficiencies specifically formulated for white and rosé wines.
• Lallemand ML Red Boost is formulated from specific inactive yeast fractions, peptides and polysaccharides, which enhance the bacteria's resistance to high polyphenol levels (which can have an inhibitory effect on malolactic fermentations) and favor the health of the bacteria.

Other practices that promote or influence malolactic fermentation:

• Skin contact before or during fermentation promotes bacterial growth and malolactic fermentation by the release of increased amounts of mannoproteins during fermentation, and with the reduced production of toxic mid-chain fatty (carboxylic) acids (Jackson, Wine Science).
• Clarification by racking, fining, centrifugation or other similar process reduces the likelihood of MLF by directly reducing the population of lactic acid bacteria and encouraging the removal of nutrients.
• Thermovinification, raising crushed grapes to high temperatures before fermentation, may impede malolactic fermentation (Lallemand, MLF guide).
• Sur lie maturation can increase the release of mannoproteins and reduce the production of toxic mid-chain fatty (carboxylic) acids (Jackson, Wine Science).
• Malolactic fermentation in oak cooperage can increase the relative color intensity by increasing anthocyanin–tannin polymerization (Jackson, Wine Science).

​Inhibition of Malolactic Fermentation
Alternatively, to preserve fruit aromas in white wine like Chardonnay, malolactic fermentation is not desired, therefore inhibition is preferable. According to Jackson in Wine Science, the following can be used to inhibit MLF:

• Wine storage at or below 10 °C.
• Early and frequent racking.
• Early clarification.
• Acidification of high pH musts or wines.
• Minimal maceration.
• Avoidance of sur lies maturation.
• Maintenance of a total sulfur dioxide content above 50 mg/liter.
• Lysozyme has been approved in several countries to retard or prevent the action of lactic acid bacteria, and has the advantage of being more effective at higher pH values. It has no detectable effect on wine aroma, taste (Bartowsky, Costello et al., 2004), or effervescence.
• Sterile filtration may be used, depending on the likelihood of post-bottling malolactic fermentation, as in-bottle malolactic fermentation can generate clouding, petillance (from the released carbon dioxide trapped in the bottle), and be the source of off-odors.

The Hydration Process12

• Oenococcus oeni is rehydrated n warm water.
• Once rehydrated, it is added to a water, grape juice and nutrient solution to further develop.
• Oenococcus oeni may then acclimatized to the wine by inoculation of the culture in a small portion of the wine.
• Once acclimitized it is mixed into the wine via stirring.

​For additional insight into Malolactic Fermentation: 
Lallemand. (2013, April 18). Understanding Varietal Aromas During Alcoholic And Malolactic Fermentations. Lallemand Wine. Retrieved June 24, 2022, from www.lallemandwine.com/wp-content/uploads/2014/07/Cahier-2013-2014-final.pdf

Costello, P. J. (2015). Malolactic Fermentation: Importance of Wine Lactic Acid Bacteria in Winemaking (R. Morenzoni & K. S. Specht, Eds.). Lallemand Incorporated. https://www.lallemandwine.com/wp-content/uploads/2015/10/Lallemand-Malolactic-Fermentation.pdf

Sulette Malherbe, Andreas G J Tredoux, Hélène H Nieuwoudt, Maret du Toit, Comparative metabolic profiling to investigate the contribution of O. oeni MLF starter cultures to red wine composition, Journal of Industrial Microbiology and Biotechnology, Volume 39, Issue 3, 1 March 2012, Pages 477–494, https://doi.org/10.1007/s10295-011-1050-4

Virdis, C., Sumby, K., Bartowsky, E., & Jiranek, V. (2021). Lactic acid bacteria in wine: Technological advances and evaluation of their functional role. Frontiers in microbiology, 11, 612118.https://doi.org/10.3389/fmicb.2020.612118

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Sur Lie Maturation [13]

Traditionally used in Burgundian and some Loire white wines, sur lie maturation primarily influences the flavor of the wine by imparting secondary aromas of toasty, bready, and umami notes through the breakdown of the yeast cells in autolysis. Beyond this, sur lie maturation can also provide other benefits.  

Aging Terms

• Sur lie: Bottles are aged on the lees.
• Sur latte: Bottles are stacked on their sides, with or without lees. Latte refers to the thin wooden strips used between the bottle layers.

• Lees Contents
• Mechanisms of Reaction
• Process
• Influence on Wine

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Types of Lees [14]
Heavy lees

• Precipitate within 24 hours immediately post-fermentation, and are composed of large particles (greater than 100 micrometers). These consist of grape particulates, agglomerates of tartrate crystals, yeasts, bacteria, and protein-polysaccharide-tannin complexes.
• Aging on heavy lees can result in off-aroma and flavors, and a depletion of sulfur dioxide.

The Content of Wine Lees
Lees are a generic term for any wine sediment, therefore the contents of fermentation lees differ from fining lees.

Fermentation lees are primarily [15]:

• 25-35% tartaric salt.
• 35-45% microorganisms (predominantly yeasts).
• 30-40% organic residues of grape solids and phenolic precipitate.

The content of wine lees is influenced by the degree of must clarification and amount of yeast macromolecules recovered in the wine. When the must is not clarified, there is no production of  yeast macromolecules.

 Autolysis15
In Latin, autolysis (auto=”self” and lysis = “breakdown“) is the process of yeast cell degradation after its death. This results in the release of the cell’s contents into the wine (the concentrated form known as yeast extract) accompanied by reduction of dry weight of the lees. Fornairon-Bonnefond (2002) provided great insight into Autolysis which we have summarized.

The Process of Autolysis16
Yeast autolysis can be divided into two parts:
Proteolysis: Degradation of the cell’s inner protein-containing substances by enzymes. During this process, as the cell’s contents become more disorganized, the cell’s enzymes interact with more cell components. The key enzymes include:

• The proteolytic enzyme (protease) which breaks down proteins into amino acids and peptides.
• Nuclease enzymes, which degrade RNA and DNA, yielding compounds including nucleosides, mononucleotides, and polynucleotides.

​Autolysate: Degradation of the cell wall and the cytoplasm by glucanase enzymes, causing it to become porous and leak the autolysate (the mixture of degraded cellular components) into the wine. This process can be further broken down into parts:

• Through hydrolysis, β-glucanases liberate mannoproteins covalently bonded to glucans.
• The glucans are then hydrolyzed by a soluble β-glucanase present in the medium.
• The mannoproteins are further hydrolyzed by β-mannosidase or by the proteases released during proteolysis. Fornairon-Bonnefond (2002) notes that Feuillat et al. (1989) found the mannans in the cell wall are released without hydrolysis, whereas the glucans are hydrolyzed to give short chains or monomers, resulting in more glucose than mannose being released.

Factors Influencing Autolysis

Temperature and pH
The wine environment in which autolysis occurs typically contains ethanol and temperatures of 15-18 °C and a pH of 3-4. These conditions are less than ideal for autolysis, and cause the process to occur slowly, so longer periods are required for complete autolysis (Dharmadhikkari, 2016).

Other Factors that Influence Autolysis
(Fornairon-Bonnefond, 2002)

• The ionic composition of the medium. Calcium and magnesium favor autolysis at 30 °C.
• The ethanol content of the medium.Proteolysis is more rapid at 10% (v/v) than at 12% (v/v).
• Oxygen concentration. Too much aeration and a lack of nitrogen or energy in the medium can also interfere with both structural and functional cellular processes and accelerate autolysis.
• Bâtonnage (stirring of lees) can increase enzyme contact with other yeast cells.

Duration of Autolysis18:

• Typical Wine Aging Duration: 9 months to 10+ years
• ~3 months (80 days): Cells plasmolyze, and most typical membrane-bound organelles disappear.
• 18 months: The optimal duration for effervescence production and foam stability, because of the accumulation of polysaccharides. Further aging seems to result in polysaccharide hydrolysis (breakdown).
• 8-11 years: The polysaccharides in the outer layer change.

Primary Byproducts of Autolysis
Ribonucleic acids (RNAs), which can function as flavor enhancers in food products.
Lipids and sterols, including fatty acids predominantly derived from the yeast cell walls, can be involved in the formation of esters, ketones and aldehydes.

Nitrogenous substances, including amino acids and oligopeptides. The quantity and presence of the specific nitrogenous compounds is difficult to make generalizations about, since they are influenced by a multitude of factors. Amino acids have been related to enhancements in both wine texture and aroma, with a strong positive correlation between amino acid concentration and wine score (AWRI - Lees Contact).

Polysaccharides and Mannoproteins
In autolysates, the majority of the sugar is in the form of polysaccharides, with very little glucose or reducing sugar being found. Of those polysaccharides, one of the most important and ubiquitous groups are mannoproteins, which make up the majority of the polysaccharides in the yeast’s extracellular matrix. These are chains of predominantly mannose (a monosaccharide) linked to a small percentage of protein molecules. Zoecklein (2012) provided the following insight:

• The quantity is influenced by yeast strain, fermentation temperature, must turbidity (increased turbidity generally means lower mannoprotein concentration), the medium it is in, lees contact time, and stirring of lees.
• Mannoproteins released during fermentation are more reactive than those released during the yeast autolysis process in modifying astringency.

Procedure
The Presence of Lees During Aging

• If the wine is aged on its lees with no fining, mannoproteins interact and fortify the existing aroma components.
• If the wine is fined before aging, mannoproteins are removed and will not be present to augment the existing aroma components (Zoecklein, 2012).

Duration of Lees Aging

• Traditionally in France, wines were clarified in March to keep them on lees throughout the entire 8-12 month aging process, with periodic stirring (Fornairon-Bonnefond et al. 2002).
• Currently, wine is left in contact with the lees for 3 to 6 months. [20]

Aging Container

• Typically, sur lie maturation occurs in the fermentation barrel, because a large surface area/volume ratio (small cooperage) increases the diffusion of nutrients and flavorants from yeasts into the wine (AWRI - Lees Contact).
• High volume tanks should not be used for sur lie maturation, as the highly reductive substances which limit wood induced oxygenation would be increased in these tanks, and can cause the release of reductive, or sulfur containing compounds (Zoecklein, 2012).

Bâtonnage ( stirring of the lees)
When done, there is some minimal oxygen accumulation in the wine, as the lees can scavenge oxygen entering through the barrel staves and bunghole. The frequency of bâtonnage is up to the producer, and will impact the overall oxygen exposure of the wine.

Benefits:

• Prevents the production of reductive sulfur off odors through some oxygen exposure.
• Periodic bâtonnage increases the mannoprotein level and amount of yeast-derived amino acids (Zoecklein, 2012).
• Stirring also changes the sensory balance between fruit, yeast, and wood by enhancing the yeast component and reducing the fruit, and, to a lesser degree, the wood component (Zoecklein, 2012).

Challenges:

• Excessive stirring can introduce too much oxygen, leading to the loss of SO2 and potentially the formation of acetaldehyde and acetic acid (AWRI -Lees Contact).
• The oxidative process can increase the acetaldehyde and acetic acid concentration (Zoecklein, 2012).

For more on the benefits and challenges of oxygen in wine, read the section on “Oxygen” at hawaiibevguide.com/wine-fermentation-physical-conditions.

​Influence of Lees on Wine
Influence on Color and Mouthfeel
As lees absorb polyphenols like tannins and anthocyanins and adsorb oxygen that can limit the anthocyanin tannin polymerization, they ultimately impact color and mouthfeel. In particular, lees can:

• Reduce the susceptibility to oxidative browning in white wine.
• Reduce the likelihood of oxidative pinking by adsorption of the responsible precursor molecules and directly reducing oxygen (Fornairon-Bonnefond, 2002).
• The adsorption of oxygen can limit the anthocyanin-tannin polymerization, resulting in an increase in dry tannin perception. However, this may be mitigated by the release of lees components, which can soften mouthfeel and reduce the perception of astringency and bitterness (Zoecklein, 2012).
• Reduce wood tannin astringency by binding polysaccharides with free ellagitannins, thus lowering the proportion of active tannins (Zoecklein, 2012).
• Amino acids have been related to enhancements in both wine texture and aroma, with a strong positive correlation between amino acid concentration and wine score (AWRI - Lees Contact).

Wine Aroma
Direct contribution to aroma compounds:
Volatile yeast metabolites, including ethyl octanoate and ethyl decanoate, add a fruity characteristic to the wine.
Adsorption of compounds by lees:

• Provide a sense of sweetness as a result of binding with wood phenols and organic acids. [21]
• May reduce 4-ethylphenols (barnyard, Band-Aid aroma).22
• Lees can bind with wood derived compounds like vanillin, furfural, and methyl-octalactones (Zoecklein, 2012).

Mannoproteins in particular influence wine aroma, as they can:

• Reduce the volatility of some aroma compounds by forming aggregates with the molecule, thereby decreasing the accessibility of the hydrophobic sites of the protein. 23
• Encourage the growth of malolactic bacteria (Zoecklein, 2012).
• The reductive action of lees helps to protect against oxidation of certain fruit aroma compounds (Zoecklein, 2001).

White Wine Protein Stability
Increasing lees contact lowers the need for fining agents like bentonite, because the additional mannoproteins add stability (Zoecklein, 2012).

Tartrate and Protein Stability

• Increased lees contact time increases the likelihood of potassium bitartrate stability, since mannoproteins inhibit crystal formation (Zoecklein, 2012).
• Mannoprotiens can, if derived from particular yeast, minimize haze production from heat-unstable proteins.24

The oxygen-scavenging capacity of lees can result in lower concentrations of SO2 being required to prevent oxidation (AWRI - Lees Contact).

Challenges

• Sur lie maturation can potentially cause reductive tones. This can be mitigated by using “barrel-aged lees” (those that have been in barrels for two months or more), especially if done in tanks greater than 1000 gallons, as the low oxygen concentration at the bottom of such tanks can create problems (Zoecklein, 2001).
• Sur lie maturation can increase the likelihood of Brettanomyces in barreled wine (Zoecklein, 2012).

Other Lees
Post-fining lees: If bentonite is used, fining lees may have significant amounts of wine. Centrifugation or cross-flow filtration can be used to recover the liquid.

For more insight, read:
Dharmadhikari , M. (2016, September 9). Yeast Autolysis. Iowa State University. Retrieved June 23, 2022, from http://www.extension.iastate.edu/wine/publications/yeast-autolysis/ Retrieved from: https://www.researchgate.net/publication/279689501_New_trends_on_yeast_autolysis_and_wine_ageing_on_lees_A_Bibliographic_review

Zoecklein, B. (2012, July 16). Enology notes #162. Virginia Tech. Retrieved June 23, 2022, from https://www.apps.fst.vt.edu/extension/enology/EN/162.html

Fornairon-Bonnefond, C., Camarasa, C., Moutounet, M., & Salmon, J.-M. (2002). New trends on yeast autolysis and wine ageing on lees: a bibliographic review. OENO One, 36(2), 49–69. https://doi.org/10.20870/oeno-one.2002.36.2.974

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Blending Wine

​Blending is essentially using two or more wines to make a product greater than the sum of its parts. The process is currently driven by art and based upon the blender’s past experience as Gas Chromatography Mass Spectrometry is more general than specific. The specific goals for blending vary, though the general approach is to utilize the variations between different wines to create an end product that is greater than the sum of its parts.

• General Approach to Blending
• Pre-Fermentation Blending
• Post-Fermentation Blending

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General Approach to Blending
The separation of grapes into smaller lots has the advantage of permitting selective blending, based on the attributes of specific wines and distinctive qualities of fruit from different sites or maturity grades.

• Wines produced from grapes of especially high quality are usually kept and bottled separately to retain their distinctive attributes.
• Grapes from famous vineyards, if blended with wine from other sites, regardless of quality, would prohibit the owner from using the site name, and would significantly reduce the market value of the wine.
• Blending takes into account regional blending rules.
• After blending the wine is often aged for several weeks, months or years before bottling.
  

Regional Blending Rules
Many wine regions have rules governing where the grapes are required to be grown, what grapes may be used in the blend, and if there are any minimum requirements for the proportion of a particular cultivar in a blend. Generally, the more prestigious or finite the region, the more restrictive the legislation.


Scientific Research on Blending
Scientific research on blending has been focused on predicting the final color of the wine because of its influence on quality perception. Blending diagrams using colorimeter readings have been developed. Computer-aided systems have been proposed to facilitate this activity:
Coletta, R., & Trombettoni, G. (2016). Constrained global optimization for wine blending. Constraints, 21(4), 597-615. https://hal-lirmm.ccsd.cnrs.fr/lirmm-01275597/document

Pre-fermentation
The vintner determines which grapes will be fermented together. Typically, fermentation occurs by cultivar, though co-fermentation may occur.
Co-Fermentation:

• Blending typically occurs after crushing, and prior to fermentation.
• “Field Blends” were historically blended in the field, where grapes of different cultivars were randomly planted ​and not separated out during harvest. Modern field blends are not necessarily co-fermented.

Post-Fermentation Blending
Timing of Post-Fermentation Blending

• Red wines: Typically blended in the spring following the vintage.
• Sherry: Fractional blending occurs periodically throughout maturation.
• Sparkling wine: Blending occurs in the spring after harvest to allow the unique features of the wines to become apparent.

Post-Fermentation Blending Styles
House styles or proprietary blends
Consistency from year to year is the priority above vintage, variety, or vineyard origin. This technique is most often used in the production of fortified and sparkling wines. Proprietary blends can refer to table wines with a house style.

Varietal blends
The famous Bordeaux style blends and Rhone style blends were historically made with the grapes which grow best or originate in the region or subregion. However, through hundreds of years of trial and error, styles eventually came to represent grapes that enhanced each other. This is the reason for the Meritage and Super Tuscan blends that mirror the approach to blending in Bordeaux, and the GSM blends (references a red wine blended from Grenache, Syrah, and Mourvedre) that mirror those from Rhone.

100% single varietal wines
To enhance the flavor of the final wine, wines made from different growing locations or different production processes can be blended together.

Blending Techniques
Beyond blending different varietals, blending wine can take many different approaches, depending on the style of wine being created. This can take the form of blending wines of different:

Regions, though from the same cultivar. This is common when high enough volumes of grapes are used that they cannot be obtained exclusively from one growing region. On a wine label, this may read “California'' instead of “Napa Valley.” Similarly, due to Napa’s sub-AVAs (American Viticultural Area), a label could read “Napa” instead of “Stag’s Leap” or “Mt. Veeder.” This is not to say the wine is inferior, however, as blending wines from different Winkler Regions (warmer and cooler regions) can create flavors that cannot be achieved from sourcing grapes exclusively from one region.

Clones of the same varietal
Clones can express differently, so some winemakers will vinify clones separately to better control the final blend.

Vineyard lots
Different parts of the vineyard can have different soil and aspect, so the grapes can vary in flavor. This technique is more common for wineries that use small fermentation vessels, because the size of each vineyard lot is typically small, and the labor expense to individually separate out each lot can be high.

Press fractions
Blending wine made from free run juice with wine made from a higher ratio of press fractions during poor vintage years can enhance body and color. This is because press fraction wine is higher in pigment and tannins. Typically, wines from exclusively red or white cultivars are blended, however styles that blend both are not unusual.

Oak Treatments
Oaked wine can be blended with unoaked wine to control the level of oak flavor imparted. Also, as oak barrels are expensive, it can be a cost control measure. Alternatively, wine aged in different types of oak can also be blended, for example Quercus alba (American white oak) with Quercus robur (European white oak).

Other Blending Styles
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Colors of grapes
Though not typical for all regions, this is common in the production of Champagne, where many wines are a blend of Chardonnay (white), Pinot Noir (red) and Pinot Meunier (red). It should be noted that these wines are typically white in color, except if rosé Champagne is being made, then a red wine is blended in to produce the pink color.

Vintage Years
Known as reserve wine, this is a common practice in Champagne where the seasons are highly variable. A portion of the previous year’s wine is saved so that house styles can be consistent. Côte-Rôtie cru wines are made from red Syrah blended with white Viognier grapes.25 Cassa et al (2012) studied different blends of Syrah and Viognier and found26: The basic composition of the wines were unaffected by the co-fermentation treatment. Also, the additions of Viognier grapes to Syrah grapes at the rates studied did not result in an enhancement of the chromatic and phenolic composition of the final wines. Rather, Viognier additions of less than 10% lowered most chromatic parameters in the final wines, with 20% additions leading to a lower concentration of anthocyanins and flavonols, suggesting dilution of these compounds.

Sweet reserve (süssreserve in German) Unfermented grape juice is preserved by tartrate stabilization and sulfur dioxide or sterile filtration, and stored for up to a year.27 This can then be blended back into wine to add sweetness. Grape concentrate can also be used, and it is easier to store.

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​Resources and Suggested Reading

1. Coletta, R., & Trombettoni, G. (2016). Constrained global optimization for wine blending. Constraints, 21(4), 597-615. https://hal-lirmm.ccsd.cnrs.fr/lirmm-01275597/document

2. Rankine, B. C., Fornachon, J. C. M., & Bridson, D. A. (2017). Diacetyl in Australian dry red wines and its significance in wine quality. VITIS-Journal of Grapevine Research, 8(2), 129. https://ojs.openagrar.de/index.php/VITIS/article/view/7415

3. Virdis, C., Sumby, K., Bartowsky, E., & Jiranek, V. (2021, January 15). Lactic acid bacteria in wine: Technological advances and evaluation of their functional role. Frontiers. Retrieved May 18, 2022, from www.frontiersin.org/articles/10.3389/fmicb.2020.612118/full

4. Understanding Varietal Aromas During Alcoholic And Malolactic Fermentations. Lallemand Wine. (2013, April 18). Retrieved May 19, 2022, from www.lallemandwine.com/wp-content/uploads/2014/07/Cahier-2013-2014-final.pdf

5. María Heras, J. (2015). Organoleptic Defects Caused By Uncontrolled Malolactic Fermentation. Lallemand Malolactic Fermentation Importance Of Wine Lactic Acid Bacteria In Winemaking. www.lallemandwine.com/wp-content/uploads/2015/10/Lallemand-Malolactic-Fermentation.pdf

6. Costello, D. P., Déléris-Bou, M., Descenzo, D. R., Hall , D. N., Krieger , D. S., Lonvaud-Funel, P. D. A., Loubser, P., Heras, J. M., Molinari, S., Morenzoni, D. R., Silvano , A., Specht, G., Vidal, F., Morenzoni, R., & Specht, K. S. (2015). MALOLACTIC FERMENTATION IMPORTANCE OF WINE LACTIC ACID BACTERIA IN WINEMAKING. Lallemand Wine. Retrieved May 19, 2022, from www.lallemandwine.com/wp-content/uploads/2015/10/Lallemand-Malolactic-Fermentation.pdf

​7. Achieving Successful Malolactic Fermentation. Australian Wine Research Institute. (2020, September). Retrieved May 19, 2022, from https://www.awri.com.au/wp-content/uploads/2011/06/Malolactic-fermentation.pdf

8. Scott Labs malolactic bacteria and nutrient choosing... Scott Labs. (2021, July). Retrieved May 18, 2022, from https://scottlab.com/scott-labs-malolactic-bacteria-and-nutrient-choosing-guide

9. Preparation of a malolactic fermentation (MLF) starter culture using freeze dried bacteria. The Australian Wine Research Institute. (2016, April 12). Retrieved May 19, 2022, from www.awri.com.au/industry_support/winemaking_resources/wine_fermentation/mlf-starter-culture/

10. The Australian Wine Research Institute. Winemaking treatment – Lees Contact. (2022, May 3). Retrieved May 19, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-lees-contact/

11. Scott labs malolactic bacteria and nutrient . choosing. Scott Labs. (2021, July). Retrieved May 18, 2022, from https://scottlab.com/scott-labs-malolactic-bacteria-and-nutrient-choosing-guide

12. Preparation of a malolactic fermentation (MLF) starter culture using freeze dried bacteria. The Australian Wine Research Institute. (2016, April 12). Retrieved May 19, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/wine_fermentation/mlf-starter-culture/

13. The Australian Wine Research Institute. Winemaking treatment – Lees Contact. (2022, May 3). Retrieved May 19, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-lees-contact

14. Zoecklein, B. (2012, July 16). Enology notes #162. Virginia Tech. Retrieved June 23, 2022, from https://www.apps.fst.vt.edu/extension/enology/EN/162.htmlenology/html

15. Fornairon-Bonnefond, C., Camarasa, C., Moutounet, M., & Salmon, J.-M. (2002). New trends on yeast autolysis and wine ageing on lees: a bibliographic review. OENO One, 36(2), 49–69. https://doi.org/10.20870/oeno-one.2002.36.2.974 Retrieved from: https://www.researchgate.net/publication/279689501_New_trends_on_yeast_autolysis_and_wine_ageing_on_lees_A_Bibliographic_reviewageing_review

16. Dharmadhikari , M. (2016, September 9). Yeast Autolysis. Iowa State University . Retrieved June 23, 2022, from http://www.extension.iastate.edu/wine/publications/yeast-autolysis/

17. Feuillat, M., Freyssinet, M., & Charpentier, C. (1989). L’élevage sur lies des vins blancs de Bourgogne. II. Evolution des macromolécules: Polysaccharides et protéines. Vitis, 28, 161-176. https://doi.org/10.5073/vitis.1989.28.161-
176https://176

18. Piton, F., Charpentier, M., & Troton, D. (1988). Cell wall and lipid changes in Saccharomyces cerevisiae during aging of champagne wine. American journal of enology and viticulture, 39(3), 221-226. https://www.ajevonline.org/content/39/3/221.short

19. 17. Andrés-Lacueva, C., Lamuela-Raventós, R. M., Buxaderas, S., & de la Torre-Boronat, M. D. C. (1997). Influence of variety and aging on foaming properties of cava (sparkling wine). 2. Journal of Agricultural and Food Chemistry, 45(7), 2520-2525.45(2525.

20. Winemaking Treatment . The Australian Wine Research Institute. (2022, May 3).
Retrieved June 23, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-lees-contact/

21. Zoecklein, B. (2001, April 15). Enology notes #25. Retrieved May 19, 2022, from https://www.#www.apps.fst.vt.edu/extension/enology/EN/25.html

22. Chassagne, D., Guilloux-Benatier, M., Alexandre, H., & Voilley, A. (2005, June). Sorption of wine volatile phenols by yeast lees. sciencedirect.com. Retrieved May 20, 2022, from https://doi.org/10.1016/j.foodchem.2004.05.044

23. Chalier, P., Ango, B., Delteil, D., Doco, T., & Gunata, Z. G. (2005, September 15). Interactions between aroma compounds and whole mannoprotein isolated from Saccharomyces cerevisiae strains. academia.edu. Retrieved May 20, 2022, from https://www.academia.edu/17953501/Interactions_between_aroma_compounds_and_whole_mannoprotein_isolated_from_Saccharomyces_cerevisiae_strains

24. Dupin, I. V., McKinnon, B. M., Ryan, C., Boulay, M., Markides, A. J., Williams, G. P., & Waters, E. J. (2000, August). Saccharomyces cerevisiae mannoproteins that protect wine from protein haze: Their release during fermentation and Lees contact and a proposal for their mechanism of action. Journal of agricultural and food chemistry . Retrieved May 20, 2022, from https://pubs.acs.org/doi/10.1021/jf0002443

25. Cote Rotie. Vins Rhône. (n.d.). Retrieved May 20, 2022, from https://www.vins-rhone.com/en/vineyard/appellations/cote-rotie

​26. Casassa, L. F., Keirsey, L. S., Mireles, M. S., & Harbertson, J. F. (2012). Cofermentation of Syrah with Viognier: evolution of color and phenolics during winemaking and bottle aging. American journal of enology and viticulture, 63(4), 538-543. Retrieved from: https://www.researchgate.net/publication/259557609_538full_Casassanet/Casassa

27. Robinson, J., & Harding, J. (Eds.). (2015). The Oxford companion to wine. American Chemical Society.