In a recent blog, I listed some of the many factors that can affect a wine’s flavors. One of the factors is the type of vessel chosen by the winemaker to ferment the wine. So, let’s take a closer look.

The three most common fermentation vessels are made of either oak, stainless steel or concrete. Each of these can affect the flavor of the wine due to the degree to which the wine is exposed to oxygen.

Fermentation in Oak 
Oak fermentation barrels allow for the gradual influx of oxygen which helps to softened tannins and acid while developing a ‘rounder’ more balanced wine. Oak itself also imparts flavors. French oak is known to yield more subtle flavors like clove and spice to a wine while creating a silkier, smoother mouthfeel, while American oak typically imparts aromas of vanilla and coconut. And, the degree to which these flavors are imparted varies by the level of ‘toast’ created on the barrel during its production. So, for instance, a barrel with a ‘medium’ toast will impart less flavors than a barrel with a heavy toast. Finally, once an oak barrel has been used three to four times, the majority of the flavors have been extracted and it becomes a ‘neutral’ barrel that imparts little to no flavors.

Fermentation in Stainless Steel

Unlike oak, stainless steel fermentation vessels can be tightly sealed so as to allow little to no oxygen exposure of the wine during the fermentation process. And, a winemaker may fill the top of the tank (the headspace) with inert gas to drive out all of the oxygen. This makes for brighter, fresher fruit-forward wines. The stainless steel imparts no flavor characteristics to the wine. Stainless steel tanks are also used because they offer optimal refrigeration capabilities when a winemaker wants to cold-ferment the wine.

Fermentation in Concrete

Concrete-type vessels have been used to ferment wine for as long as wine has been made. Concrete tanks can be open for oxygen exposure, or sealed like stainless steel to avoid oxygen. The concrete itself is quite neutral so it doesn’t impart significant flavors like oak, but it can add mineral-like flavors to the wine.