Glycerin: the subtle sweetness in your wine

Glycerin, a colorless and odorless liquid, plays a subtle yet significant role in the world of wine. This compound, also known as glycerol, is the third most important product generated during wine fermentation, following ethanol and carbon dioxide. Glycerin's sweet taste and oily texture enhance the drinking experience, though it remarkably contributes little to the wine's flavor in terms of aroma.

Glycerin arises from the action of yeasts, essentially as a metabolic byproduct or waste of the microorganism before its death. The enzyme glycerol-3-phosphate dehydrogenase (GPDH) catalyzes its formation. Chemically, glycerol, or 1,2,3-propanetriol, is a glycolic alcohol with the formula C3H8O3, forming the backbone of fatty acids in lipids.

The yeast strains used in winemaking significantly influence glycerol production. However, several other factors also contribute, such as the grape variety and its maturity at harvest, and various winemaking practices, including pH, SO2 concentration, fermentation temperature, aeration, yeast inoculation levels, and nitrogenous compounds.

Despite its sweet taste and smooth texture, glycerin doesn't majorly alter the wine's flavor since it is an incolor and odorless liquid. However, glycerol positively affects wine quality by acting as a substrate for important color and flavor compounds soluble in it, like carotenoids. It also contributes to sweetness and mouthfeel, especially when present in the wine at levels between 3 and 9 grams per liter.

Wines produced by Saccharomyces yeast strains, a common family in winemaking, generate substantial glycerol amounts. This enhances the wine's quality, positively influencing color and tactile sensations such as body, smoothness, oiliness, viscosity, and more.

Glycerin is partly responsible for the "legs" or "tears" forming on the inner walls of the glass when wine is swirled. In very old wines, bacterial degradation of glycerin over time leads to the production of acrolein, an unstable compound that imparts a penetrating and unpleasant odor (reminiscent of rancidness and burnt rubber).

Beyond its role in wine, glycerol is present in all oils and animal and vegetable fats. It's a common ingredient in various industries, including cosmetics (soap and lubricants), textiles, pharmaceuticals, and more.

Glycerin's presence in wine showcases the complex chemistry behind winemaking, underscoring how even seemingly minor components can significantly impact the final product's taste, texture, and overall quality. As research continues to evolve, the understanding of glycerin's role may lead to further refinements in the art and science of winemaking, ensuring that each glass of wine is a harmonious blend of flavor, aroma, and texture.