How Does Fermentation Effect Wine?

In the previous post, I mentioned that one of the byproducts of fermentation are long chain polymers which affect the flavor of wine. In this article, we will take a closer look at how fermentation influences the resulting flavor of your wine. We will identify the additional products of fermentation, explain the roles of those products in creating a wine's flavor profile, and identify common wine additives which enhance flavor during fermentation.

While winemaking is a simple process, the chemistry of wine is extremely complex. There is a lot going on at the molecular level that we can't see or detect, until we taste our wine. Let's take a closer look at some of the components of wine which are produced or affected by fermentation.

The primary product of fermentation is alcohol, which is produced when the yeast consumes the sugars found in grapes. Sugar is developed in the fruits during the growing season, and is affected by heat and photosynthesis. Grapes grown in higher temperatures and exposed to more direct sunlight will produce higher levels of sugar than those which are grown in cooler climates where the skies are more overcast, or the days are shorter. Grapes grown in warmer climates have thicker skins, which means the concentration of flavors locked in the skins will be much more intense, while grapes grown in cooler climates will produce lighter and more delicate flavors.

If fermentation finishes before all of the sugar is consumed, the remaining sugar may be detectable in the flavor of the wine. This is known as residual sugar, which can only be detected above 10 g/L. Residual sugar can neutralize or balance the acid in the wine, and is not a bad thing.

Another product which fermentation brings out in the wine is acid. Acid levels in colder climate wines are much higher than those created from grapes grown in warmer regions. Acid can be detected in the wine by a prickly feeling on the tongue and a generation of saliva in the mouth. If you've ever bitten into a lemon, you have experienced the sensation of acid on your palate. In addition to the tart flavor of the lemon, the physical reaction to the acids in the lemon is very distinct. Your salivary glands go into overdrive, and your mouth and tongue experience a tingling sensation as your body reacts to them.

The third component which fermentation produces is glycerol. Glycerol is colorless and odorless, but it produces a thickness and smoothness on the pallet which is referred to as the body of the wine. Glycerol levels are determined in part by the ripeness of the grapes and also the strain of wine yeast that is used in fermentation. Wines with high glycerol levels are often referred to as velvety, soft, or smooth. Like residual sugar, glycerol contributes to the sweetness of the wine as well.

The fourth component which impacts the flavor and aroma of wines is polyphenols, which impact the color of the wine and serve as a source of tannins. Tannins produce chemical compounds which create taste sensations of bitterness and dryness. Polyphenols are found in the skins and the seeds of the great. A wine that is high in tannins will create a dry sensation in the mouth, similar to the feeling you have after you've eaten a handful of walnuts. You will probably also detect a bitterness similar to very strong tea or coffee. The tannins produced by the polyphenols contribute to the wine's complexity, but they also act as an antioxidant, which will extend the life of the wine in the bottle.

If you add oak during fermentation, you are introducing another level of complexity to the flavor of your wine. Oak contains chemical compounds which can release aromas of vanilla, smoke, leather, tobacco, and many other elements during fermentation.

In addition to these five categories of products produced during fermentation, there are hundreds of aromatic compounds which provide countless combinations of flavors and aromas in your wine. These compounds are called esters. Esters are the chemical compounds which our nose detects and associates with a particular image.

When you sniff a rose, for example, the rose is producing esters which are absorbed by the sensors in your nose. Based on your experience, the chemical process which occurs causes your brain to associate those particular chemicals with the flower. Anytime your nose detects that particular chemical composition, your brain immediately informs you that there are roses nearby.

This amazing and complex feature of our biology allows us to detect thousands of very distinct aromas. In winemaking, these aromas occur in many different combinations to create the various flavors associated with each type of grape. The distinct combinations which occur in each variety of wine are due to the specific chemical compounds found in the cells of the grape skins.

Each type of grape carries a unique cocktail of chemicals which are formed during the growing process and dependent upon the soil composition and weather patterns of the region where the grape was grown, and the genetics of that particular variety. When the grapes are crushed, the skins release the chemical compounds into the juice. Fermentation works on these compounds to produce the aromatic esters we find in wine.

As you can see, there is a lot going on during fermentation. This is one of the amazing and beautiful things about winemaking.

What questions do you have for me about the effects of fermentation on winemaking? Be sure to post your questions in the comments section. In my next post, we will discuss the types of yeast used in winemaking. Be sure to add your name to the mailing list so you don't miss it!