Previous successful fermentation articles have been more aimed at white grape varieties because there is substantial crossover in winery activities. There are several processes to be discussed that are more unique to red winemaking.
The right type and size vessels will depend primarily on the size of the winery and its expect ferment batch size. The specific types of red varieties to be fermented and wine style will also play a major role. Fermentation vessels available include open-top tanks, closed-top tanks, rotary fermentors, bins, and oak barrels.
Read more about red fermentation vessels.
State of the Grapes
The state of grapes during fermentation can have a major effect on fermentation kinetics. Harvest method can be the determining factor since mechanically harvested fruit will obviously not be in pristine whole clusters when it arrives at the winery. Mechanically-harvested fruit may need nothing more than to be transferred directly into the fermentation vessel upon arrival, though a quick run through the destemmer is usually ideal to help pull out any material other than grapes (MOG)
Harvest-picked fruit gives winemakers more options for fermentation.
Whole Clusters - Fruit is transferred directly into fermentation vessel. This can lead two substantially different fermentation methods.
- Carbonic maceration is a method most commonly associated with Beaujolais wine, and more recently with 'Noveau' wines being produced in the United States. Carbonic maceration is intracellular fermentation in a carbon dioxide rich environment that promotes anaerobic fermentation. Over time, the weight of the grapes in the fermentation vessel will crush fruit at the bottom and aerobic fermentation will take hold. The primary objective behind this method is to produce a lighter bodied fruity wine with limited phenolic extraction.
- 'Whole cluster fermentation' is a slightly confusing team, and many winemakers would argue it is the same as above. Carbonic maceration undoubtedly occurs and is usually desired to some extent. Nevertheless, the concept here is is to promote phenolic extraction: the large amount of grape solids creates a large cap during fermentation, the stems create flow of juice through the skins increasing contact, and more aggressive cap management promotes aerobic fermentation. This is commonly associated with long cold soaks and extended maceration.
Whole berries - Fruit is gently destemmed but not crushed before transferred into fermentation vessel.
The whole berries are allowed to undergo partial 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.
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 often 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.
It is not uncommon for a winery to employ all of the above methods on various portion of production. Experimentation is one 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.