Determination of Glycerol in beer/wine/cider

Glycerol is a natural by-product of alcoholic fermentation. Its production increases under yeast stress conditions (high wort osmolarity, nutrient deficiency, ethanol stress). Variations in glycerol concentration contribute to the mouthfeel and the perception of “smoothness” in beer. At low glycerol concentrations (1–2 g/L), the sensory contribution is minimal and almost imperceptible. The beer may appear “drier” or lighter. At medium to high concentrations (3–10 g/L), glycerol begins to have a noticeable effect, imparting a rounder, fuller, and more velvety sensation on the palate. At excessive glycerol concentrations, above 10 g/L—uncommon in traditional beer but possible under stressed fermentations or in the presence of contaminations (e.g., wild yeasts or lactic acid bacteria)—the result may be unbalanced or give a “sticky” mouthfeel.

The presence of polyhydric alcohols determines, in wine, enveloping sensations, also called roundness, which make the softness of the wine. Among the polyalcohols which are formed during the fermentation there are mannitol, sorbitol, butylene glycol and glycerol. The latter is particularly interesting because the wine can be present with values ranging between 5-18 g/L and is also produced in large quantities by noble rot during the production of passito wines. This explains the softness and elegance of this type of wine.