Fermented Beverages

From Sugar to Alcohol: The Chemistry Behind Fermented Beverages

Alcoholic beverages are, at their biochemical core, all products of the same basic process seen in bread-making -- yeasts, principally strains of Saccharomyces cerevisiae, fermenting sugars into ethanol and carbon dioxide. What differentiates wine from beer from whisky from toddy is not fundamentally different biology, but rather three practical variables: the raw material fermented (which supplies the sugar), the specific strain and conditions used, and -- critically -- whether the fermented product is subsequently distilled.

Wine and Beer

Wine is produced by fermenting the natural sugars present in grape juice using yeast; the yeast may occur naturally on grape skins or be added as a cultured starter. As fermentation proceeds, the yeast converts the grape sugars into ethanol, and the resulting liquid is then aged, clarified and bottled -- without any distillation step. Beer follows a broadly parallel process but uses malted cereal grains (typically barley) as the starting source of fermentable sugar; the malted grain is first mashed to release its sugars, hops are added for bitterness and preservation, and yeast is then introduced to ferment the resulting liquid ("wort") into beer.

Toddy: A Traditional Undistilled Beverage

Toddy is a traditional fermented beverage, widely consumed in parts of India, prepared from the sap collected from various palm trees (such as coconut or palmyra palm). The sugar-rich sap is collected and left to ferment naturally; wild yeasts present in the environment (often including strains of Saccharomyces) act on the sugars in the sap, converting them into a mildly alcoholic drink, again without any distillation. Because it is undistilled, freshly tapped toddy has a relatively low, gently increasing alcohol content, and its character changes noticeably over the course of a single day as fermentation continues.

Distilled Spirits: Whisky, Rum and Brandy …