Saccharomyces cerevisiae has been used for at least eight millennia in the production of alcoholic beverages (41). Along with ethanol and carbon dioxide, fermenting cultures of this yeast produce many low-molecular-weight flavor compounds. These alcohols, aldehydes, organic acids, esters, organic sul- fides, and carbonyl compounds have a strong impact on prod- uct quality. Indeed, the subtle aroma balance of these com- pounds in fermented foods and beverages is often used as an organoleptic fingerprint for specific products and brands (42). Food fermentation by yeast and lactic acid bacteria is accom- panied by the formation of the aliphatic and aromatic alcohols known as fusel alcohols. Fusel oil, which derives its name from the German word fusel (bad liquor), is obtained during the distillation of spirits and is enriched with these higher alcohols. While fusel alcohols at high concentrations impart off-flavors, low concentrations of these compounds and their esters make an essential contribution to the flavors and aromas of fer- mented foods and beverages. Fusel alcohols are derived from amino acid catabolism via a pathway that was first proposed a century ago by Ehrlich (13). Amino acids represent the major source of the assimilable nitrogen in wort and grape must, and these amino acids are taken up by yeast in a sequential manner (23, 32). Amino acids that are assimilated by the Ehrlich path- way (valine, leucine, isoleucine, methionine, and phenylala- nine) are taken up slowly throughout the fermentation time (32). After the initial transamination reaction (Fig. 1), the resulting -keto acid cannot be redirected into central carbon metabolism. Before -keto acids are excreted into the growth medium, yeast cells convert them into fusel alcohols or acids via the Ehrlich pathway. Current scientific interest in the Ehrlich pathway is sup- ported by increased demands for natural flavor compounds such as isoamyl alcohol and 2-phenylethanol, which can be produced from amino acids in yeast-based bioconversion pro- cesses (14), as well as by the need to control flavor profiles of fermented food products. The goal of this paper is to present a concise centenary overview of the biochemistry, molecular biology, and physiology of this important pathway in S. cerevi- siae.