Read previous posts on Successful Fermentation - Introduction, Selecting the Right Yeast (Part I, Part II), Preparing Juice/Must for Inoculation, Indigenous Yeast, Inoculation, Yeast Propagation (Part I, Part II, Part III), Fermentation Monitoring.
While my previous posts are all applicable to red varietals, winemakers must consider several other processes that effect their fermentation. This starts immediately upon reception of the fruit, whether it has been mechanically harvested or hand-picked. While many will argue a strong correlation between quality and hand-picked grapes, I know plenty of good wine that is produced via mechanical harvesting. Mechanically harvested fruit may need nothing more than to be transferred directly into fermentation vessels upon arrival, though often a quick run through a destemmer may help pull out MOG (material other than grapes).
Some wineries opt for sorting fruit upon arrival at the winery. This method is usually reserved for hand-picked fruit, and often deemed too time consuming and costly by most wineries though it can make a difference in wine quality. I personally believe hand-picked fruit should arrive at the winery clean (free of MOG and poor quality fruit); this is really a matter of ensuring properly trained vineyard staff.
Fermentation vessel is the first major consideration in the winery. This is dictated by what equipment is available at a particular winery, the lot size of grapes, and the cap management regime (read about red varietal fermentation vessels here). The most important factor is vessel dimensions; tall and slender vessels have less surface area at the top, meaning more skin contact, and vice-versa.
The second consideration is the state of the grapes:
Whole clusters - Fruit is transferred directly into fermentation vessel. The grapes are allowed to undergo carbonic maceration, intracellular fermentation in a carbon dioxide rich environment that promotes anaerobic fermentation (instead of traditional aerobic fermentation). The presence of stems in the fermenting vessel does two things: imparts compounds from the stems (primarily phenolics) and creates channels through skins allowing more juice movement through the cap and thus higher skin contact. Over time, the weight of the grapes in the fermentation vessel will crush fruit at the bottom and aerobic fermentation will take hold. This method aims at creating a more fruity finished wine with lower phenolic structure (often used with Pinot Noir and Gamay Noir, most notably in Beaujolais wines).
Whole berries - Fruit is gently destemmed but not crushed before transferred into fermentation vessel. The whole berries are allowed to undergo carbonic maceration, while the lack of stems limits the movement of free juice and decreases skin contact. Again, the weight of the grapes in the fermentation vessel will crush
fruit at the bottom over time and aerobic fermentation will take hold. This method is used in lieu of whole cluster to avoid compounds imparted by the stems (for instance, with grapes that have insufficiently ripe stems). Winemakers may chose to add some percentage of stems back into the
fermenting vessel to gain some of the positives of their presence
Crushed berries - Fruit is destemmed and crushed before transferred into fermentation vessel. This allows high skin contact with juice during fermentation, resulting in more phenolic and flavor extraction. Wines meant for long-term aging will benefit from this method as it promotes more complex tannin compounds that will take longer to soften. This method is the most commonly used, particularly with Bordeaux varietals such as Cabernet Sauvignon.
Winemakers will often use combinations of the above methods. This is usually done by blending finished wines after fermentation or maturation, though some will combine techniques in singular fermentation vessels. Experimentation is my favorite part of winemaking. It really comes down
to the type and quality of grapes one has, and the wine style desired.
Winemakers need to develop a strong understanding of the fruit they work with, trial different methods, and determine what is best for each lot. I have tried a whole number of different methods such as whole berries through cold soak (to be discussed in Part II) while promoting skin breakdown through cap management during aerobic fermentation or adding back stems or whole clusters into whole and/or crushed berry fermentations.
Continue to Red Varietals Part II to read about cold soaking, cap management, and additives.