Whole Cluster Fermentations: Practical considerations

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. 

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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.