Congeners fusel alcohols

("Fusel": German for "rotgut" or "hooch")

The molecules made by mistake tend to be longer chain alcohols, acids and esters, all of which add flavors (usually unpleasant) to the product, and many of which are toxic. These are called "congeners," which means "with from the birth" - they were produced at the same time and by the same processes as the alcohol we desire. The composition of these congeners, collectively known as "fusel oils", or more correctly fusel alcohols, varies with the carbohydrate source and yeast variety, but is mostly isopentanol and 2-methyl-1-butanol, with about 20% isobutanol, 3-5% n-propanol, and small amounts of other alcohols, esters and aldehydes. Carefully selected strains of yeast and carefully managed temperatures and concentrations result in cleaner, more pleasant fermentations. Since the rate of chemical reactions generally doubles for every 10° C (18° F) temperature rise, high quality fermentations conducted at low temperature take more time. This compromise of time vs. quality is present everywhere in the production of alcohol-containing beverages. Managing the conditions of fermentation is the primary method of producing specific flavor profiles in fermented beverages.

Many different sources of sugar may be fermented into alcohol, and many others either will not ferment, or cannot be fermented by particular yeasts. Differences in the type of the sugars available, the species of yeast available and the quality of the local water have led to a huge variety of different types of alcohol-containing beverages around the world. The next section of this chapter discusses a few of the more common types, and how to prepare them for distillation.

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