How does the selection of yeast impact the production of glycerol during fermentation and how does glycerol contribute to the overall sensory profile of wine?

Yeast selection significantly influences glycerol production during fermentation, and glycerol plays an important role in the sensory profile of wine. Glycerol is a polyol (sugar alcohol) produced by yeast as a byproduct of alcoholic fermentation. The amount of glycerol produced varies depending on the yeast strain, fermentation conditions, and must composition. Certain yeast strains, particularly some Saccharomyces cerevisiae strains and certain non-Saccharomyces yeasts, are known to produce higher levels of glycerol than others. Selecting these high-glycerol-producing strains can enhance the wine's mouthfeel and perceived sweetness. Glycerol contributes to the wine's mouthfeel by increasing its viscosity and smoothness. It adds a sensation of roundness and body, making the wine feel fuller and more pleasant on the palate. Although glycerol is not technically a sugar, it can contribute to the perception of sweetness. It has a slightly sweet taste, although it is much less sweet than glucose or fructose. The presence of glycerol can balance the acidity and tannins in the wine, making it more approachable. Factors other than yeast strain also influence glycerol production. Higher fermentation temperatures can increase glycerol production, as can osmotic stress. Nutrient deficiencies, particularly nitrogen deficiency, can also increase glycerol production as yeast alter their metabolism. Glycerol levels in wine typically range from 5 to 10 grams per liter, but can be higher in certain wines produced with specific yeast strains or under particular fermentation conditions. While glycerol contributes positively to mouthfeel, excessive levels can make a wine seem flabby or unbalanced. Therefore, winemakers carefully consider yeast selection and fermentation management to achieve the desired glycerol level and overall sensory profile.