Whole Cluster Fermentations: 3 Fractions, 2 Fermentations

Interest in whole cluster fermentation might be trendy, but the technique itself is not new. Crushing and destemming of grapes was only made possible by the invention of efficient crusher/destemmers in the 19^thCentury¹. Reports from Champagne in the 19^th Century document a full week between harvest and processing, indicating that intracellular fermentation, one aspect of whole cluster inclusion, was widespread and descriptions of winemaking from Bordeaux from this time indicate whole clusters were regularly included¹.. Even with the advent of destemmers, inclusion of at least a portion of whole clusters has remained a part of winemaking in many Old World regions such as Beaujolais, Rioja and Georgia² and is currently utilized around the world in regions such as Burgundy, the Rhone, Australia, and California^1,3. Carbonic maceration, a specific technique using 100% whole clusters, was invented by Flanzy in 1934 after a failed experiment in preserving grapes. Flanzy’s work (and that of many others) provided research into the chemistry of grape autofermentation, shedding light on the production of the distinctive flavors and aromas found in whole cluster fermentations used throughout the ages^1,2.

Wines produced from whole cluster fermentations are characterized by distinct aromas and flavors of kirsch, cherry, strawberry and raspberry¹. They are often lighter in body and color than traditional fermentations, though not always, and can have herbal qualities and rustic tannin structure. The overall sensory impact of using whole clusters is influenced by many factors, including the proportion of whole clusters included, the variety and the ripeness of the fruit. In his reflection on whole clusters, Jamie Goode cites winemakers using whole cluster for “greater complexity and silkier tannins”, “to add freshness”, for their “fragrance and perfume”, and ability to “add strength and firmness to the tannins” while others avoid whole clusters because they think they “dull the fruit”, make the wine “too herbal”, or give it a “mulch/compost character”³. Goode’s own assessment is that the move to include clusters is in line with a trend toward “elegance over power”³. 

The First Fermentation

In any whole cluster fermentation, grapes may be found in three different environments (Figure 1); the proportion of grapes in each greatly influences the sensory characteristics of the resulting wine. Some grapes are intact clusters in a CO₂-rich atmosphere, and initially experience autofermentation (Fraction 1). Some grapes will be crushed at the bottom of the tank where they are subject to alcoholic fermentation by yeast (Fraction 3). In between these two are intact grapes immersed in the juice and must of the crushed grapes (Fraction 2). Grapes inthis fraction undergo a modified autofermentation and are more likely to break down as the fermentation progresses. 

The proportion of grapes in any one of these fractions depends on winemaking protocols and grape variety. The proportion of crushed grapes (Fraction 3) may be intentionally increased by foot stomping or destemming. Some varieties are more likely to break up during loading than others. For example, Merlot and Petit Verdot will have more crushing than thick skinned Cabernet Franc (Matthieu Finot, personal communication). The dimensions of the fermentation vessel also contribute to the amount of crushed vs. intact grapes. Tall thin tanks have a higher column of grapes weighing down the bottom clusters while shorter, broader vessels have less crushing. 

From: Butler, Joel. Beaujolais Master Class

Autofermentation of grapes occurs in Fractions 1 and 2. 

When grapes are picked, the cells inside the berries are still alive, and thus need a source of energy to maintain their cellular processes and organization. Under normal circumstances, they use oxygen from the atmosphere to break down sugar through aerobic respiration to produce CO₂, water and energy. However, when atmospheric oxygen falls below 1%, the metabolism of the grape shifts to internal fermentation². Carbon dioxide is heavier than oxygen, so when it is present, it will settle at the bottom of the tank and displace oxygen from the bottom up. In whole cluster fermentation, CO₂ may be added through gas sparging, dry ice, or production by yeast fermentation of crushed berries¹. Once present, CO₂ is quickly absorbed into the grape berries, which absorb up to 60% of the berry volume of CO₂¹. 

The presence of CO₂ in grape cells triggers several changes in berry metabolism. In the absence of oxygen, grape cells begin to convert sugar to ethanol through glycolysis followed by a final step that produces ethanol, a process much the same as yeast fermentation. Ripe berries already possess alcohol dehydrogenase, the enzyme used for the last step of this conversion², however, unlike a yeast fermentation, in grapes this reaction only proceeds until 1.5-2% alcohol has been produced. At that point, the accumulated alcohol becomes toxic to the cell, causing a number of consequences that have effects on the resulting wine. By-products of fermentation including glycerol, acetic acid, and succinic acid begin to accumulate¹. Cell membranes break down, releasing organic acids that cause a decrease in cellular pH, and further inhibition of fermentation¹. Phenolic compounds are also released from cellular compartments; anthocyanins and eventually tannins leach from skins into the pulp. Seed tannins are rarely leached, as they require higher levels of alcohol to break down the seed coat¹.

The CO₂ rich, anaerobic environment of the grapes has many other effects on cellular metabolism beyond those caused by the accumulation of alcohol:

• Grape pectinases are induced by CO₂, leading to the breakdown of pectin that holds cells together. The pulp loses its solid texture¹.
• Up to 50% of the grape malic acid may be metabolized to other acids and ethanol without the accumulation of lactic acid. Tartaric and citric acids may also be affected, depending on the grape variety^1,2. 
• Modification of the metabolic pathway that usually leads to the production of amino acids instead leads to the production of volatile compounds such as ethyl cinnamate, benzaldehyde, ethyl decanoate, and many others. These compounds contribute to aromas of strawberry, raspberry, cherry and kirsch that distinguish whole cluster fermentations^1,2.
• Lower oxygen presence limits the oxidation of fatty acids that can lead to production of C6 compounds hexyl acetate and hexanol, known for vegetal, tomato-leaf flavors and aromas^1,2.
• Intracellular enzymes break down proteins, releasing amino acids that can later serve as nutrients for yeast and bacteria as well as and precursors to flavor and aromas^1,2.

Grapes in Fractions 1 and 2 experience autofermentation to some degree, however, the more grapes are submerged in fermenting must (Fraction 2), the less character of autofermentation is found it the wine. This is because ethanol produced by fermenting must diffuses into the intact grape berries, increasing the alcohol concentration inside the grape. Initially, this triggers production of aromatic compounds¹, and increases the extraction of phenolics^1,4, but it also leads to much faster cell death⁴. Additionally, bathing berries in alcohol leads to faster breakdown of skins, meaning the berries stay intact for a shorter period of time. Though this process limits the effects of autofermentation, it does lead to some preservation of varietal characters, which can be lost during autofermentation⁴. Also, submersion of burst berries in the fermenting must further increases phenolic extraction. This means whole berry fermentations, or those with lower proportion of whole cluster inclusion, may have less strawberry/raspberry/cinnamon aromas but higher color, tannin, and varietal aromas.

The alcoholic fermentation (Fraction 3)

The activities of the fermentation in Fraction 3 are beneficial to the remaining fractions. CO₂ production displaces oxygen, encouraging autofermentation in berries and limiting aerobic yeast such as Acetobacter and Klockera from producing acetic acid and ethyl acetate. A robust yeast fermentation also produces heat, which has several benefits (see below)¹.

Though Fraction 3 undergoes a familiar yeast fermentation, there are several aspects to this fermentation that are different from a traditional fermentation. The initial volume of juice is usually very low, but additional juice, sugar, and nutrients are added over time as berries burst. This means the kinetics of the yeast population is governed less by a ‘boom and bust” than by steady buildup. Rather than building up, ethanol, the toxic by product of fermentation that eventually inhibits yeast, is partially removed by diffusion into intact grape berries. As a consequence, at the time of pressing, there is usually a healthy population of yeast on the order of 1x10⁷cells/ml, capable of robust completion of fermentation post pressing¹.  This is not the case, however, if the fermentation is allowed to go through extended maceration, since the yeast may have run out of sugar. 

Fraction 3 also differs markedly from traditional fermentations due to the presence of stems. Stems can make up 2-5% of the overall weight of the grape cluster and their presence has an impact on fermentation in both physical and chemical ways³. Physically, stems are found interspersed among skins and seeds in the cap, loosening compaction. This allows better mixing during cap management and less stratification of temperature in the fermentation. Generally, these fermentations are characterized by greater retention of volatiles that give varietal character, and gentler extraction of seed phenolics³. Chemically, stems add potassium, which can lead to high pH as potassium binds with tartaric acid to form insoluble bitartrate. Stems also contain methoxypyrazine (over 50% of the pyrazine in grape clusters are found in the stems⁵) that can lead to vegetal/herbal notes. Stems also contain phenolics of their own, which can be seen as a benefit or detriment depending on the wine. Paul Draper from Ridge Vineyards avoids using stems in his Cabernet Sauvignon and Zinfandel, as he feels he already has an abundance of tannin³. However, others, like Matthieu Finot of King Family Vineyards, use whole clusters to add to the tannin profile (personal communication), especially in varieties that lack them. These tannins, though challenging in young wines, soften over time to show silky texture and add spiciness to the wine, adding to its ageability³. This is probably why whole cluster fermentation is often applied to low tannin varieties like Pinot Noir and Syrah³.

Though the physical and chemical processes active in the three fractions are similar in any whole cluster fermentation, the outcomes depend on a number of decisions by the winemaker, including the proportion of the fractions, the duration of the initial fermentation, and the temperature. Whole cluster inclusion can be anywhere from a small proportion (5-10%) to 100%, and this proportion will have significant effects on the finished wine. In true carbonic maceration, for example, clusters remain whole with care taken to limit Fractions 2 and 3 as much as possible. These wines are pressed early and most of the fermentation is completed post-pressing. This approach maximizes the effects of autofermentiton with little to no impact of stems, seeds, or skins, producing fruity, early releasing wines with little aging potential. By contrast, many winemakers take the approach used for production of Cru Beaujolais, where 100% whole clusters are used, but a small proportion is crushed (by loading or foot stomping) to initiate alcoholic fermentation in the vat. The wine continues to be held in contact with skins, seeds, and stems as berries break down, allowing significant extraction of phenolics and better aging capacity. 

The temperature of the fermentation this stage can also have a profound effect on the resulting wine. As with any fermentation, warmer temperatures speed all reactions, including those involved in cellular breakdown and formation of volatile compounds. Higher temperature also aids in the extraction of phenolic compounds, leading to more structured wines. In traditional fermentations, high temperature can lead to loss of volatile compounds due to high CO₂ production and simple volatilization. However, in whole cluster fermentations, many of the volatile compounds are still contained in intact berries, not subject to these losses. Optimal temperatures for flavor development in carbonic maceration is thought to be 30-32°C (86-90°F) while in Beaujolais, the preferred temperature for fermentation is 18-22°C (64-72°F). Whole cluster fermentations that are too cool have only limited impacts of autofermentation^1,2,6.

Pressing and the second fermentation

The decision of when to press a whole cluster fermentation depends on the goals for the wine. For true carbonic maceration, grapes are pressed when they have reached 2% internal alcohol and no longer show signs of additional autofermentation. This usually occurs after 5-8 days in a CO₂ rich atmosphere at 32°C (90°F), but can take up to 15-20 days at lower temperatures (15°C, 60°F). In a Beaujolais-style fermentation, wine is pressed when Fraction 3 nears the end of its fermentation and CO₂ evolution is slowing. In more traditional fermentations with whole cluster inclusion, extended maceration is also sometimes done.

There is also a marked difference between free run and press juice in these fermentations. The free run represents wine from Fraction 3, which is likely to be tannic, potentially bitter, and nearly finished with fermentation. In carbonic maceration, this is the least preferred portion. The press fraction will contain aromatic compounds including fruity esters from autofermentaiton and unreleased volatile varietal compounds, color and skin tannins. This will also include additional sugar that will likely be released when intact berries are pressed. In carbonic maceration or Beaujolais style whole cluster fermentations, a healthy yeast population has built up and will finish fermentation promptly. However, if the must in Fraction 3 has finished fermentation, the yeast population may have begun to die off and the must has likely cooled off, making it difficult to complete the fermentation. Additionally, if malic acid bacteria or Brettanomyces are present, release of sugar can lead to rapid accumulation of acetic acid. For this reason, some winemakers will add lysozyme or chitosan to the press juice to prevent spoilage (Matthieu Finot, personal communication) while others will keep the fractions separate at least until the completion of fermentation. Due to depletion of malic acid during autofermentation, malolactic fermentation usually proceeds quickly and is done early². 

References

(1) Jackson, R. S. Wine Science: Principles and Applications, 4 edition.; Academic Press: Amsterdam, 2014.

(2) Tesniere, C.; Flanzy, C. Carbonic Maceration Wines: Characteristics and Winemaking Process. Adv. Food Nutr. Res. 2011, 63, 1–15. 

(3) Goode, J. Stemming the Tide. The World of Fine Wine 2012, No. 37, 90–97.

(4) Bisson, L. F. Geographic Origin and Diversity of Wine Strains of Saccharomyces. American Journal of Enology and Viticulture 2012, 63 (2), 165–176. 

(5) Zoecklein, B. W. Herbaceous Character in Red Wines. Enology Notes, 2006.

(6) Bisson, L. F. Grape and Must Processing. In Intoduction to Wine Production Course; Davis, California, n.d.

When and why to include whole clusters in your winemaking plans

When considering whether or not to include whole clusters in your winemaking plans, it is important to keep in mind that the effects of a 30% whole cluster inclusion are different than 100% whole cluster fermentation, and carbonic maceration, with early pressing has different effects than a Cru Beaujolais style approach. A good example is the effect of whole cluster fermentation on varietal character.

True carbonic maceration (100% whole cluster with little to no extraction) can lead to a decrease in varietal character due to less extraction of flavor and aroma precursors from skins. However, a small amount of whole berry inclusion (30%) in a traditional fermentation can lead to increased varietal character as precursors are preserved in berries until after the heat of fermentation, which may lead to volatilization, has passed¹. For strongly varietal wines, such as Bordeaux varieties, more than 85% of the fruit must go through carbonic maceration to mask the varietal aromas².

At times, moderation of varietal characters is the goal:

• Autofermentation adds an appealing fruitiness, even in normally neutral varieties^1,2. This fruitiness comes from the production of esters that usually last 6-12 months during aging, but eventually are replaced by a more aged character³.
• Carbonic maceration has been shown to mask some of the intense, foxy and raspberry aromas of native or hybrid grapes^2,3. 
• Limiting extraction through whole cluster fermentation is a useful technique for making earlier release wines from tannic varieties, such as Tannat². 
• This technique has also been investigated for its ability to lower acidity in overly acidic varieties, particularly native and hybrids. These varieties sometimes have an abundance of malic acid that inhibits malolactic fermentation; carbonic maceration reduces malic acid without the production of lactic acid, leading to lower TA, higher pH, and better success in malolactic fermentation⁴. The acid reducing power of carbonic maceration was equal to chemical methods such as potassium carbonate and Acidex additions⁵.  
• Autofermentation itself also leads to lower levels of vegetative character, as fewer C6 compounds (tomato leaf) are formed^2,3. This effect is somewhat moderated if the wine has a longer maceration on stems post berry burst.

Several aspects of whole cluster fermentation affect the color of the wine. Anthocyanin molecules are found in the skin of the grapes, and are readily extracted, however they are also unstable and easily lost early in the life of the wine if not stabilized by polymerization with other phenolics⁶. In fermentations with large proportions of whole clusters, berries are not broken and there is less extraction of chemical components off the skins of the grapes. In addition, early pressing leads to lower tannin content, which limits stabilization of color. Higher pH due to potassium leaching from stems and consumption of acids during autofermentation can further limit color in wines fermented with a high proportion of whole clusters. Lower levels of whole cluster, or longer maceration time after berries have begun to burst, can increase color extraction and stabilization.

How to include whole clusters in your winemaking plans

If you are thinking of including whole clusters in your winemaking plans, here are a few practical things to keep in mind:

1. For whole cluster fermentations, grapes must be fully intact with no sign of breakage or disease². Any clusters with compromised berries will provide a rich environment for spoilage organisms already resident on the grapes. Spoilage will be allowed to progress much longer than in a traditional fermentation due to the lack of a fully anoxic, alcohol bathed environment. Acetic acid and ethyl acetate are the hallmarks of a whole cluster fermentation gone wrong.
2. You must have a ready source of CO₂. This could come from positive pressure of CO₂ gas, addition of dry ice, or an active yeast fermentation at the bottom of the tank. All oxygen must be displaced to protect against oxidative spoilage but also to trigger grapes to begin autofermentation. 
3. Choose your tank wisely. Plan more fermenter capacity for a longer period of time. Whole clusters take up more space than destemmed or crushed fruit, and these fermentations are slower. Also, the proportions of the fermentation vessel (short and fat vs. tall and skinny) will affect how much crushing of grapes you have at the bottom, and thus what proportion of grapes in each fraction^2,3.
4.  Not all grape varieties are the same. Cabernet Franc, with its thick skins and small berries, takes longer to break down than Merlot or Petit Verdot (Matthieu Finot, personal communication).
5. Be careful when doing additions. It is difficult to estimate the final volume of wine. Be conservative with additions such as tartaric acid to make sure you do not over-add. In true carbonic maceration, chaptalization is often done after pressing². 
6. Be careful with cap management depending on your goals. Bathing whole clusters in fermenting juice by pumping over or punching down may help minimize spoilage organisms, but it may also introduce oxygen for these spoilage organisms to metabolize. Additionally, alcohol on grape skins makes them break down faster, leading to less impact of autofermentation².
7. Be prepared for the release of additional sugar when pressing. If you are separating free run from press fraction, this sugar will be found predominantly in the press fraction. Make sure you give the yeast a good environment to complete fermentation (heat if needed, press before all sugar is gone). If malolactic fermentation has begun in fraction 3 due to extended maceration, either separate fractions or stop malolactic with lysozyme or chitosan to all alcoholic fermentation to finish without acetic acid buildup.
8. Check your acidity. Due to the potential of breakdown of acids during autofermentation, as well as the influence of potassium leached from stems, whole clusters often lead to higher pH/lower acid wines. 

References

(1) Bisson, L. F. Grape and Must Processing. In Intoduction to Wine Production Course; Davis, California, n.d.

(2) Jackson, R. S. Wine Science: Principles and Applications, 4 edition.; Academic Press: Amsterdam, 2014.

(3) Tesniere, C.; Flanzy, C. Carbonic Maceration Wines: Characteristics and Winemaking Process. Adv. Food Nutr. Res. 2011, 63, 1–15.

(4) Beelman, R. B.; Mcardle, F. J. Influence of Carbonic Maceration on Acid Reduction and Quality of a Pennsylvania Dry Red Table Wine. Am J Enol Vitic. 1974, 25 (4), 219–221.

(5) Gadek, F. J.; Diamond, F.; Hearney, M.; McMullin, M.; Szvetecz, M. A.; Verano, F. P. Preliminary Investigation of Deacidification Methods and Carbonic Maceration of French Hybrid Wines. Am J Enol Vitic.1980, 31 (1), 90–94.

(6) Managing Wine Quality; Reynolds, A. G., Ed.; Food Science, Technology adn Nutrition; Woodhead Publishing: Philadelphia, 2010; Vol. 2.

The most popular topic for WRE experimentation so far has been the inclusion of whole clusters or carbonic maceration in red wine fermenations. To find full reports for all of these experiments, you can search "whole clsuter inclusion" under the red wine fermentation tab. Attached here is a table with a brief summary of the experiments completed through 2018. 

Winemakers Research Exchange is grateful to have had Winemaker Matthieu Finot of King Family Vineyards join us on Instagram Live for a discussion of whole cluster fermentation. We discussed his 2019 experiment as well as some tips for how to use this technique successfully in the winery.

Watch Video Here

Summary

Whole cluster fermentation has the potential to provide increased complexity, fruitiness and strong tannins to the wine. However, whole cluster fermentations can also include bitter phenolics and spoilage from oxidative yeast. The purpose of this study was to test a procedure for whole cluster fermentation that limited spoilage while developing a rustic, powerful style of Petit Verdot. Key elements in the protocol include using warm fruit and foot stomping to produce a rapid start of fermentation in the liquid fraction that protects the whole clusters from spoilage and triggers autofermentation. Finished wines from 100% whole cluster, 50% whole cluster/50% destemmed and 100% destemmed treatments showed very similar basic chemistry with no indication of spoilage in any of the treatments. Color decreased with increasing proportion of whole cluster. Sensory impacts included additional fruitiness and tannic grip with increasing proportion of whole clusters. This protocol successfully produced clean wines with different styles.

Introduction

Utilizing whole clusters rather than destemmed or crushed fruit has several consequences for fermentation leading to fruitier wines often with less color and potentially sharper tannins. Several chemical processes are at play:

1. Anaerobic metabolism inside the grape can lead to loss of malic acid, increase in some fruity aromas and flavors and loss of some varietal character^1–3.
2. Some fruity aromas and flavors are retained inside berries that would otherwise be lost to volatilization during fermentation³.
3. Inclusion of stems can lead to some loss of color, increases in potassium (with drop in acid), and potential increases in phenolics such as catechin and tannin⁴.
4. Whole cluster fermentations are often cooler than traditional fermentations. It takes longer for a cap to form. Cap management after berries begin to break down is more successful at breaking up the cap fully due to less compaction of berries and stems^1,4. 
5. There is often less extraction of phenolics from skins and seeds as there is less contact time for alcohol-based solubilization¹.

In addition, whole cluster fermentations include potential for pockets of oxygen persisting for some time, allowing for spoilage by aerobic yeast and bacteria. Some whole cluster fermentations are characterized by acetic acid and ethyl acetate, leading to aromas of vinegar and nail polish remover¹. However, these fermentations can also lead to increased complexity and a more rustic style of wine. The purpose of this experiment was to implement a series of strategies to allow for whole cluster fermentation in Petit Verdot that avoids spoilage and leads to a rustic, powerful wine. Specifics of each step with rationale are outlined in the following protocol. 

Methods

There were three treatments: 

1. 100% destemmed fruit
2. 50% destemmed, 50% whole cluster
3. 100% whole cluster

For all treatments, grapes were loaded into bins immediately after harvesting. Processing of un-chilled grapes allowed for a fast start to fermentation. In whole cluster fermentations, spoilage by non-Saccharomycesyeast (Klockera) and bacteria (Acetobacter) resident on the grapes can lead to high levels of acetic acid and ethyl acetate. By starting fermentation quickly, CO₂ is produced that displaces oxygen, a needed substrate for spoilage.

Whole cluster treatment

Grapes were loaded into TBins from harvest bins as whole clusters. After 1/3 of the whole clusters were loaded into the TBin, grapes were stomped to produce enough juice for the initial fermentation to begin. A well-mixed vineyard starter culture of yeast was added to inoculate the fermentation. Appendix A contains a protocol for preparation of the vineyard starter culture. Stab Micro M (14 g/hL) was also added to further prevent microbial spoilage.

Standard protocol (for destemmed and 50/50 lots)

Grapes were destemmed to TBins the same day as harvest with the addition of 20 ppm SO₂. One bin received 100% destemmed fruit while the other received 50% (by weight) destemmed fruit, 50% whole clusters added to the bin at the same time. Bins were inoculated with the same well-mixed vineyard starter culture as the whole cluster bin. 

For all treatments, cap management occurred twice per day. The destemmed and 50/50 lots were punched down while the whole cluster lot was foot stomped until a cap formed, at which time it was punched down. All bins were pressed the same day (10/23) for a total of 24 days of overall maceration. Wine was allowed to settle for 1-2 days prior to racking and transfer to identical barrels. Malolactic conversion occurred naturally in barrel. At the completion of malolactic fermentation, 3 g/hL Stab Micro (Enartis), 2.5 g/L tartaric acid and 66ppm SO₂ were added to each barrel.

Results

Grapes were harvested at 22.1° Brix with a pH = 3.48 and TA = 5.7 g/L. There were no large differences in general wine chemistry between lots (Table 1). Studies in other varieties have shown pH increases with increasing proportion of stems, presumably due to increased potassium leaching from stems in whole cluster fermentations. That trend is not evident here. Perhaps this is due to the high potassium levels found in Petit Verdot skins, present in all three treatments.

The volatile acidity is notably similar for all three treatments. Accumulation of volatile acidity is a primary concern in whole cluster fermentations and was a driver of this experiment. From these data, this protocol appears to be effective in combatting early spoilage due to oxidative yeasts and bacteria. Color (Figure 1) and anthocyanin content (Table 2) decreased with increasing proportion of whole clusters.

Full sensory analysis was not possible due to social distancing guidelines during the COVID-19 outbreak. The winemaker and research coordinator report increased fruitiness and tannic grip in the 100% whole cluster fermentation while the control was characteristic of a well made Virginia Petit Verdot. The 50% whole cluster treatment showed intermediate impacts, as expected. 

Table 1: General wine chemistry for three treatments of Petit Verdot (ICV labs)

Figure 1: Color intensity for three treatments of Petit Verdot (ICV Labs)

Table 2: Rapid phenolic analysis for three treatments of Petit Verdot (mg/L) (ETS Labs)

References

(1) Jackowetz, N.; Li, E.; de Orduña, R. M. Sulphur Dioxide Content of Wines: The Role of Winemaking and Carbonyl Compounds. Appellation Cornell 2011, 3, 1–7.

(2) Tesniere, C.; Flanzy, C. Carbonic Maceration Wines: Characteristics and Winemaking Process. Adv. Food Nutr. Res. 2011, 63, 1–15. https://doi.org/10.1016/B978-0-12-384927-4.00001-4.

(3) Bisson, L. F. Grape and Must Processing. In Introduction to Wine Production Course; Davis, California, n.d.

(4) Goode, Jamie: Stemming the Tide, World Of Fine Wine, Issue 37, 90-97. 2012 http://www.worldoffinewine.com/news/stemming-the-tide-4869650 (accessed Apr 30, 2020).

Appendix A: Protocol for preparing a vineyard starter culture

To prepare a starter for the ambient fermentation, 4-5 days prior to harvest, clean clusters were picked and crushed into a cleaned and sanitized 6 gallon bucket with a removable lid. A single SO₂ addition of 30 ppm was made. The container of crushed fruit was kept in the vineyard to limit exposure to commercial yeast in the winery and allow the native yeast fermentation to begin. Temperature of the starter was kept near 26°C (by shading or sun exposure). The starter was monitored for Brix depletion and temperature daily (or twice per day if it is moving briskly). The starter was oxygenated after 2 or 3 days. When the starter was around 1.045 - 1.030 (8 - 12° Brix), pomace in the bucket was strained and the fermenting juice was used for inoculation. The starter was tasted before inoculation to be sure that VA and ethyl acetate are not too high.