Dehydration Rate and its Influencing Factors 

​The speed and amount of grape dehydration highly influences the final aromatic composition of the resulting wine [2]. Rapid dehydration, which is associated with high temperatures, induces very stressful metabolisms which can result in unwanted oxidation, amino acid catabolism (occurring due to the rapid cell death), and Maillard compounds. In particular, this results in:
  • Significant losses of volatiles including acids, esters, alcohols, terpenes, sesquiterpenes, benzene derivatives, and C6 compounds, as well as an increase in norisoprenoids and derivative compounds of furan, pyran, and lactones from the browning reactions.
  • Reduced fermentation caused by epiphytic microbes and therefore lower acetic acid and ethyl acetate. [5]
This makes managing thee rate of dehydration critical.  However this process can be challenging to manage as it is influenced by a multitude of factors including:
  • The Grapes Features
  • Environmental Conditions of Drying Area
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 The physical features that influence a grape’s response to water stress include: The grape cultivar, grape origin/growing conditions, grape ripeness, berry size, the compactness of the bunch, and the micropores and cracks on the berry skin’s surface.

The mechanism that these factors influence include:
  • Water primarily escapes through the grape via its skin. The rate at which water escapes is influenced by the thickness of the berry cuticle (wax layer) [3]. The cuticle is particularly dependent on the cultivar type and the grape's growing conditions.[4]
  • Grape ripeness increases evaporation by increasing peel, cell membrane permeability, and cell wall degradation. [5]
  • Metabolic processes of the grape, the most significant of which is a change from aerobic respiration to anaerobic respiration.
The environmental factors which influence the rate of dehydration including:

Temperature as it influences
The rate of evaporation as higher temperatures:
  • Accelerate evaporation due to an increase in the kinetic energy of water.
  • Can modify the structure of the grape's wax platelets. [5]

Metabolic processes as it influences cellular metabolism including a switch from aerobic to anaerobic respiration when above 30° C (86° F).

Volatile aroma compound concentration as:
  • Temperatures from 10 to 30 °C induce VOCs oxidation with a loss in the varietal volatile compounds, even if aroma complexity is reached at 20 °C.
  • Higher temperatures ( above 30 °C/ 86°F) “flatten down” varietal aromas
  • Lower drying temperatures (Below 10°C/ 50°F) can help to preserve the grape’s aromatic qualities and can reduce volatile acidity.
  • Ideal dehydration temperatures are 10 - 20 °C (50-68°F).
​Relative humidity influences the water diffusion gradient from the grape to the air with higher the humidity resulting in a slower evaporation rate. As the air immediately touching the grape is that which absorbs water, increased ventilation and airflow also increase the rate of dehydration.

The growth of epiphytic microbes, as the drying process can provide time for their development and subsequent attack on the berry. Guzzon et al (2018), noted that insects like the Drosophila suzukii fruit fly, are known for being sources of microbiological inoculants that can cause spontaneous grape fermentation or spoilage.[8] Beyond the common epiphytic microbes as noted in www.hawaiibevguide.com/wine-microbes.html, spoilage fungus can include Botrytis cinerea in the stage of gray rot, Aspergillus spp. and Penicillium which is known to produce the mycotoxin ochratoxin A as well as acetic and lactic acid bacteria.[9] To mitigate these microbiological sources, enclosed facilities with climate control can be used where allowed.[10]

Mechanical damage or microbial transfer from the winemaking team can influence grape skin and bunch integrity. Bunch integrity is important as the berry skin is prone to tearing where the stem connects to the grape.

Styles of Drying

  • Sun-Drying
  • Dehydration in Fruttaio
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Traditional Practice: Sun-Drying
Traditional Usage/Region
  • Mediterranean Basin
  • Wine styles include: Passito wines, Pedro Ximénez style fortified wines, Commandaria wines, and Santorini Vin Santo.

Process
Grape bunches are dried in the sun on straw or plastic mats or in perforated plastic crates on the ground in a single layer.

Water loss mechanisms
  • Heat from the sun.
  • Wind which removes the boundary layer allowing for a continuous vapor pressure deficit.

Time
5 days in Andalusia, to 2–3 weeks in some areas of Sicily.

Modern Variation:
Sun-Drying in transparent plastic film tunnel

Process
  • Grape bunches are placed on plastic mats or in perforated plastic crates on the ground in a single layer.
  • 10–50 m long tunnels made of plastic film are left open to create an airstream, which can be accelerated by using floor fans.

Process benefits over the traditional method
  • Protects grape bunches from rain and dew.
  • Accelerates dehydration by passively increasing the internal tunnel temperature beyond that of the air inside the tunnel.
Traditional Practice: Uncontrolled Dehydration in Fruttaio (Closed Facility)
Traditional Usage/Region
Traditionally used for Amarone wine production in Valpolicella (Italy) and in other high latitude regions where ambient conditions are not conducive to sun drying.

Process
In an in-closed facility with natural ventilation from open windows, grape bunches are dried in:
  • Crates that are stacked on each other.
  • On a straw mat.
  • Suspended from a vertical metallic mesh/net.
  • Floor fans, though not traditional, can be used to accelerate dehydration.

Water loss mechanism
The environmental conditions of the region influence relative humidity.

Modern Technique: Controlled Dehydration in Fruttaio
  • Process: Similar to the traditional process, grapes are dehydrated in crates, and straw mats, or are suspended from vertical metallic mesh/nets. However, in the drying facility, climate controls for heat and humidity are used to control the rate of dehydration.
  • Process Benefits: Reduces the high-temperature and relative humidity fluctuations that can occur in non-climate-controlled facilities thereby allowing for a more consistent product.

Modern Variation: Withering in Fruttaio with Ambient Control
  • Process: The facility has a cooling and dehumidifying plant with ventilation but also an automatic system to open the windows when the outside environmental conditions are suitable. However, this process can take a long time if using only ambient conditions.
  • Process Benefits: Closer to traditional practice and can reduce energy costs.

The Drying Process

The drying process involves several metabolic changes and changes in grape chemical composition. We have summarized the following study, and highly recommend reading it for additional insight:
[11] Costantini, V.; Bellincontro, A.; De Santis, D.; Botondi, R.; Mencarelli, F. Metabolic changes of Malvasia grapes for wine production during postharvest drying. J. Agric. Food Chem. 2006, 54, 3334–3340. ​Retrieved from:   www.academia.edu/17955346/Metabolic_Changes_of_Malvasia_Grapes_for_Wine_Production_during_Postharvest_Drying
  • Initial stages of dehydration
  • Alteration in grape cell membrane function
  • Switch to anaerobic respiration
  • Other influential compounds and enzymes
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Initial stages of dehydration
  • Most of the water is released from the rachis (stems).
  • With as little as 0.5% water loss, cell wall enzyme activity increases. A further increase in the rate of water loss accelerates respiration, ethylene production and a loss of volatiles. [5]
Alteration in grape cell membrane function due to water loss
Dehydration modifies cell tugor (the pressure outwardly exerted by the cell on the membrane) which, in turn, modifies the cell wall and plasmalemma (cell membrane of a plant).

This modification:
  • May activate oxidative enzymes involved in cell protection including lipoxygenase (LOX). The activation of LOX activity results in the oxidation of C18 polyunsaturated fatty acids in the grape skins into C6 compounds. These have grassy aroma compounds include hexenol and the aldehydes hexanal and hexenal. The accumulation in the final must varies due to reactivity with other compounds (Sanmartin 2021). For more on C6 compounds:www.hawaiibevguide.com/wine-aroma-compounds-pt-1.html
  • Reduces gaseous diffusion to prevent water loss. However, it also reduces the amount of oxygen the grape berry can use for respiration (the process of making energy from glucose which results in CO2 and water). This may lead to an energy deficit for the grape cell if the aerobic respiration pathway is used.
Switch to anaerobic respiration
The reduced ability for aerobic respiration and the higher energy demand by the grape results in a switch from aerobic to anaerobic respiration. In this process:
  • Organic acid concentration increases (pH decreases) and activates pyruvate decarboxylase. Pyruvate decarboxylase can transform pyruvate into acetaldehyde.[12]
  • Alcohol dehydrogenase (ADH) is also activated. This causes the conversion of glucose and malic acid into fermentation by-products including ethanol and CO2 via pyruvic acid.
  • Elevated temperature above 30° C (86° F), can also cause the grape’s cellular respiration to switch from aerobic to anaerobic. [7]

Other influential compounds and enzymes that influence grape metabolism during drying
During the drying process there is a biphasic spike (two increases) in compounds and enzymes that influence metabolic activity. In the Malvasia cultivar, it was found to be at 6.5% weight loss and 19% weight loss. The compounds that increase are:
Alcohol Dehydrogenase Activity (ADH)
  • Influence on wine and grapes
    • Converts ethanol to acetaldehyde.
  • Influence by dehydration
    • Drying increases ADH activity. This coincides with the second rise in proline (19% in Malvasia grapes) then continues to rise until drying is stopped.
    • Elevated temperature can increase alcohol dehydrogenase and glutamate oxaloacetate transaminase activities.
    • Mechanisms involved
      ADH is continuously synthesized during the drying process as is indicated by the consistent increase in acetaldehyde.
​​
​Proline
  • Influence on wine and grapes
    • Proline together with arginine is the primary grape amino acid.
    • It is a metabolic indicator of drought.
    • It may function as an organic osmolyte (a low-molecular-weight organic compound that helps maintain the cell’s integrity).
  • Influence by dehydration
    • A rapid rise was observed in Malvasia grapes until a weight loss of 11.7%.
    • A second significant rise occurred at 19% of weight loss in Malvasia grapes.
  • Mechanisms involved
    • The initial rise may be related to the need for free-radical detoxification due to its strong oxidation ability.
    • The subsequent proline increase is related to the need for osmotic protection.
Abscisic acid (ABA)
  • Influence on wine and grapes
    • A plant hormone involved in physiological processes including stomatal control, adaptation to stress, dormancy, and photosynthesis.
    • ABA enhances skin pigmentation by mediating the physiological state of this tissue.
  • Influence by dehydration
    • ​In the skin, it increased rapidly during the second spike. In Malvasia grapes this was 11.7% of bunch weight loss.
    • It then declined gradually during progressive dehydration.
  • ​Mechanisms involved
    • Formation occurs from mevalonic acid via the carotenoid pathway, with violaxanthin as a precursor. LOX is possibly involved in this process.
    • During water stress
    • The initial response to berry cell water loss is the accumulation of ABA, possibly due to an increase in ethylene production.
    • Due to a decrease in pH, ABA can quickly translocate from the cell's plastids to the guard cells (specialized cells in the epidermis of leaves, stems, and other organs that are used to control gas exchange)[13] thereby protecting the plant from additional water loss.
    • It is strongly activated during intracellular anaerobic fermentation.

Influence on grape chemical composition

​San Martin et al (2021) provides the following insights into the specific flavor compounds that are influenced by dehydration.
  • Sugar
  • Acidity
  • Polyphenols
  • Other Dehydration Compounds
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Sugar
Dehydration influence on sugar
  • Increased sugar content occurs through the concentrating effect of water loss.
  • Sugars can be synthesized from malic acid in the last step of the slow grape dehydration process. [5]

Influence on final wine
During fermentation, the higher sugar concentration may:
  • Increase glycerol production as the glyceropyruvic pathway is predominant during the first phases of fermentation.
  • Limit the growth and metabolism of the yeast due to the high osmotic stress, and the resulting high ethanol concentration.
  • Produce undesired concentrations of volatile acidity and other aroma compounds due to the high concentration of ethanol and high osmotic stress. For this reason, strains with high alcohol tolerance and high osmotolerance may improve the sensory characteristic of the deriving wines by emphasizing their sweet and fruity notes.[15]


Acidity

Dehydration's influence on grape acids
  • Malic acid is metabolized by anaerobic respiration. However, it is typically offset by its concentration due to water loss. It can additionally be minimized using a rapid dehydration process. [5]
  • Tartaric acid increases are due to the concentration effect, though can decrease due to salification reactions with Ca2+ and K+ ions that are freed from cell wall degradation that occurs during berry drying.
  • Citric acid is minimally affected.
  • Organic acid concentration is influenced by the rate of water loss. Slow water loss may cause overall decreases in organic acid concentration due to the longer period for which anaerobic metabolism of malic acid and tartaric acid precipitation may occur. Similarly, it has been found that temperatures in the range of 45–50 °C can increase the overall concentration of acids whereas decreases are found at temperatures of 35–40 °C.

Influence on final wine
  • The final wine is typically highly acidic due to concentration.
Polyphenols
Grape dehydration generally increases polyphenol concentration. It also changes the specific types of polyphenols as monomeric types combine to form polymeric forms. For a better understanding of polyphenols in wine: www.hawaiibevguide.com/wine-polyphenols.html

The factors influencing changes in concentration include:
  • The concentration effect caused by water loss.
  • Abiotic stress, including water stress, may stimulate anthocyanin and polyphenol biosynthesis. This may occur when ethylene (the gas that promotes ripening) biosynthesis is induced by a decrease in berry size.
  • Hydrolysis of polymerized phenols. However, polyphenoloxidase (PPO) enzyme activity can degrade or oxidize phenols if the dehydration protocol is long and non-optimal or uncontrolled as temperatures above 20 °C increase phenolic oxidation.
  • In wine, the degradation of internal skin cell layers can enhance phenol and anthocyanin extractability.
  • The high sugar concentration in berry tissues could trigger the shikimic acid pathway to synthesize phenolic compounds. For more on the shikimic acid pathway: Santos-Sánchez, N. F., Salas-Coronado, R., Hernández-Carlos, B., & Villanueva-Cañongo, C. (2019). Shikimic acid pathway in biosynthesis of phenolic compounds. Plant physiological aspects of phenolic compounds, 1, 1-15. https://www.intechopen.com/chapters/65307

Anthocyanins
Grape pigmentation and wine color have varying reactions to dehydration as they are dependent on the dehydration parameters. Traditional sun-drying, for example, is associated with oxidative browning due to enzymatic activity on hydroxycinnamic acids, anthocyanins, and flavan-3-ol derivative oxidation. Cultivar-specific trends have also been found, therefore the influence of dehydration on anthocyanins is not straightforward.
  • Specific markers for aging which increases in concentration: Peonidin-3-O-glucoside
  • Grape cultivars found in: Moscato nero d’Acqui, Raboso Piave
  • Dehydration method: Controlled conditions
  • Other anthocyanins influenced by dehydration
    • Coumaroylated compounds typically increase.
    • Acylated anthocyanins typically increase.
    • O-diphenol aglycones typically decrease due to a higher sensitivity to oxidation.
  • Dehydration influence on wine
    • Monomeric compounds generally decrease.
    • Polymeric compounds increase resulting in an increase in the color tonality.
    • Oxidation occurs during the fermentation processes. The propensity of oxidation for this molecular class varies as:
    • Cyanidin tends to be generally lower in wine produced from dehydrated grapes.
    • Malvidin typically increases in concentration and is more resistant to oxidation.
    • The polymerization reaction of anthocyanins with other phenols such as flavanol and tannins.


​Hydroxybenzoic acid
  • Specific markers for aging which increases in concentration: Protocatechic acid
  • ​Grape cultivars found in: Xynisteri
  • Dehydration method: Uncontrolled condition

Hydroxycinnamic acids
  • Specific markers for aging which increases in concentration: Caftaric acid
  • Grape cultivars found in: Xynisteri
  • Dehydration method: Uncontrolled condition​

Flavonols
  • Specific markers for aging which increases in concentration: Quercetin-3-O-glucoronide
  • Grape cultivars found in: Raboso Piave, Xynisteri
  • Dehydration method: Controlled conditions; Uncontrolled condition
​Flavan-3-ols (condensed tannins/proanthocyanidins)
Generally increase in dehydrated grapes but vary based on the applied dehydration conditions.
  • Specific markers for aging which increases in concentration: Catechin, epicatechin
  • Grape cultivars found in: Cabernet Sauvignon, Xynisteri
  • Dehydration method: Uncontrolled condition

Stilbenes
Influence by dehydration
Generally increase during dehydration and is a sign of natural dehydration of some grape cultivars. However, high levels of water loss cause a decline in their biosynthesis due to cell corruption and consequent enzymatic and non-enzymatic oxidation. Additionally, isomer concentration tended to trend in opposite directions during dehydration, and is potentially a defense response to high temperature employed in several protocols, as well as to biotic attacks from Botrytis cinerea, Plasmopara viticola, Erysiphe necator, Rhizopus stolonifera, and Aspergillus sp..

Influence on wine
The role of stilbenes on wine is inconclusinve.

Influence on aroma compounds

The general trends influencing aroma compound formation and degradation during dehydration are:
  • Water loss typically increases the concentration of total volatile aroma compounds through the concentrating effect. However, active synthesis can occur and its influence on specific aroma compounds can also decrease or have no significance. Its actual influence is highly dependent on dehydration practices and grape attributes.
  • Alcoholic fermentation by both grape cells and epiphytic yeast can result in higher alcohols, carboxylic acids, and their corresponding esters.
  • Alcohols/ Carboxylic Acids/ Esters
  • Lactones/ Terpenes/ Volatile Phenols
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Alcohols
  • The grape cells during anaerobic respiration can produce ethanol that can oxidize to acetaldehyde and acetic acid and esterifies to ethyl acetate.
  • Specific markers for aging:
    • Ethanol can be considered a marker compound for grape dehydration.
    • Isobutanol
  • Grape cultivars found in: Malvasia, Pedro Ximeénez, Sangiovese, Trebbiano
  • Dehydration method: Both controlled conditions and sun drying.
  • Other alcohols impacted by dehydration:
    Additionally epiphytic yeast which, besides ethanol and associated aldehydes, acids and esters, also produce higher alcohols of 2-phenylethanol, benzyl alcohol, isobutanol, isoamyl alcohol, and 1-pentanol. For more on the specific compounds associated with alcoholic fermentation: www.hawaiibevguide.com/wine-aroma-compounds-pt-2.html

Carboxylic Acids
  • Specific markers for aging which increases in concentration: Octanoic acids
  • Grape cultivars found in: Pedro Ximeénez
  • Dehydration method: Sun-drying
  • Other carboxylic acids impacted by dehydration: Hexanoic acid

Esters
  • Specific markers for aging which increases in concentration: Ethyl acetate, isoamyl acetate
  • Grape cultivars found in: Malvasia, Sangiovese, Tempranillo, Trebbiano
  • Dehydration method: Controlled conditions
  • Other esters impacted by dehydration: Ethyl butanoate increases in concentration.
Lactones
  • Specific markers for aging which increases in concentration: γ-valerolactone, γ-butyrolactone
  • Grape cultivars found in: Pedro Ximeénez, Tempranillo
  • Dehydration method: Sun-drying

​Terpenes
  • Specific markers for aging: Linalool oxides
  • Grape cultivars found in: Cesanese, Malvasia Moscata, Moscato nero d’Acqui
  • Dehydration method: Controlled conditions
  • Other terpenes impacted by dehydration
    • Nerol and citronellol generally increase.
    • Geraniol typically decreases due to oxidation to Geranic acid.
    • Linalool typically decreases due to oxidation to linalool oxide.

Volatile Phenols
  • Specific markers for aging which increases in concentration: Vinylguaiacol and vanillin.

These increases could be linked to cell wall degradation by enzymes including xylanase and endoglucanase, which then free non-volatile precursors for phenol biosynthesis.
  • Grape cultivars found in: Cesanese, Tempranillo
  • Dehydration method: Both controlled conditions and sun drying
  • Other phenols impacted by dehydration: 2,6-dimethoxyphenol, Acetovanillone

Maillard reaction products
  • Specific markers for aging: Furfural, 5-methylfurfural, and 5-hydroxymethyl-furfural. These give wine toasty, coffee, or chocolate aromas along with aromas of honey, raisin, dried apricot, and dried fig.
  • Grape cultivars found in: Montepulciano, Pedro Ximeénez, and Tempranillo
  • Dehydration method: Sun-drying
  • Furfural can be oxidized at high drying temperatures associated with fast dehydration protocols.

Final Fermentation
•Winemakers may reject grapes that have become diseased or damaged during drying.
•Wine can be kept sweet as is typical in many cases, or can be fermented to dry by extending the duration of fermentation. See pages 8-16 for the specific regions and styles of wine made from dehydrated grapes.

Resources and Suggested Reading

​1. Sanmartin C, Modesti M, Venturi F, Brizzolara S, Mencarelli F, Bellincontro A. Postharvest Water Loss of Wine Grape: When, What and Why. Metabolites. 2021; 11(5):318. https://doi.org/10.3390/metabo11050318

2. D’Onofrio, C., Bellincontro, A., Accordini, D., & Mencarelli, F. (2019). Malic acid as a potential marker for the aroma compounds of amarone winegrape varieties in withering. American Journal of Enology and Viticulture, 70(3), 259-266.https://www.ajevonline.org/content/70/3/259

3. McGlynn, W. (2019, June 20). Basic grape Berry Structure. Grapes. Retrieved October 25, 2022, from https://grapes.extension.org/basic-grape-berry-structure/

4. Rosenquist, J. K., & Morrison, J. C. (1989). Some factors affecting cuticle and wax accumulation on grape berries. American Journal of Enology and Viticulture, 40(4), 241-244.https://www.ajevonline.org/content/40/4/241.short

5. Bellincontro, A.; De Santis, D.; Botondi, R.; Villa, I.; Mencarelli, F. Different postharvest dehydration rates affect quality characteristics and volatile compounds of Malvasia, Trebbiano and Sangiovese grapes for wine production. J. Sci. Food Agric. 2004, 84, 1791–1800. https://www.academia.edu/17955349/Different_postharvest_dehydration_rates_affect_quality_characteristics_and_volatile_compounds_of_Malvasia_Trebbiano_and_Sangiovese_grapes_for_wine_production

6. Mencarelli, F., & Bellincontro, A. (2020). Recent advances in postharvest technology of the wine grape to improve the wine aroma. Journal of the Science of Food and Agriculture, 100(14), 5046-5055. Retrieved from: https://dspace.unitus.it/bitstream/2067/45207/1/jsfa.8910_Recent%20advances%20in%20postharvest%20technology.pdf

​7. Romieu, C.; Tesnie`re, C.; Than Ham, L.; Flanzy, C.; Robin, P.An examination of the importance of anaerobiosis and ethanol causing injury to grape mitochondria. Am. J. Enol. Vitic. 1992 , 43 , 129 - 13 Retrieved from: https://www.researchgate.net/profile/CatherineTesniere/publication/236047015_An_examination_of_the_importance_of_anaerobiosis_and_ethanol_causing_injury_to_grape_mitochondria/links/0c960535f9fc856590000000/An-examination-of-the-importance-of-anaerobiosis-and-ethanol-causing-injury-to-grape-mitochondria.pdf
​8. Guzzon, R., Franciosi, E., Moser, S., Carafa, I., & Larcher, R. (2018). Application of ozone during grape drying for the production of straw wine. Effects on the microbiota and compositive profile of grapes. Journal of applied microbiology, 125(2), 513-527. https://sfamjournals.onlinelibrary.wiley.com/doi/full/10.1111/jam.13774

9. Torelli, E., Firrao, G., Locci, R., & Gobbi, E. (2006). Ochratoxin A-producing strains of Penicillium spp. isolated from grapes used for the production of “passito” wines. International journal of food microbiology, 106(3), 307-312. Retrieved from: https://www.academia.edu/7295278/Ochratoxin_A_producing_strains_of_Penicillium_spp_isolated_from_grapes_used_for_the_production_of_passito_wines

10. Kowalczyk B, Bieniasz M, Kostecka-Gugała A. The Content of Selected Bioactive Compounds in Wines Produced from Dehydrated Grapes of the Hybrid Variety ‘Hibernal’ as a Factor Determining the Method of Producing Straw Wines. Foods. 2022; 11(7):1027. https://doi.org/10.3390/foods11071027

11.Costantini, V.; Bellincontro, A.; De Santis, D.; Botondi, R.; Mencarelli, F. Metabolic changes of Malvasia grapes for wine production during postharvest drying. J. Agric. Food Chem. 2006, 54, 3334–3340. Retrieved from: https://www.academia.edu/17955346/Metabolic_Changes_of_Malvasia_Grapes_for_Wine_Production_during_Postharvest_Drying

12. Wikipedia contributors. (2022, July 24). Pyruvate decarboxylase. In Wikipedia, The Free Encyclopedia. Retrieved 10:16, October 21, 2022, from https://en.wikipedia.org/w/index.php?title=Pyruvate_decarboxylase&oldid=1100123288

13. Wikipedia contributors. (2022, October 5). Guard cell. In Wikipedia, The Free Encyclopedia. Retrieved 11:49, October 21, 2022, from https://en.wikipedia.org/w/index.php?title=Guard_cell&oldid=1114264291

14. Wikipedia contributors. (2021, October 28). Osmolyte. In Wikipedia, The Free Encyclopedia. Retrieved 11:33, October 21, 2022, from https://en.wikipedia.org/w/index.php?title=Osmolyte&oldid=1052294946

15. de Lerma, N. L., & Peinado, R. A. (2011). Use of two osmoethanol tolerant yeast strains to ferment must from Tempranillo dried grapes:
Effect on wine composition. International Journal of Food Microbiology, 145(1), 342-348 https://doi.org/10.1016/j.ijfoodmicro.2010.12.004