Concentrations of volatile esters and acids decrease in successive cycles when the same yeast is used repeatedly to ferment pure carbohydrate substrates. The effect is independent of the sugar being fermented. Maltose produced slightly smaller amounts of several volatiles than did fructose, glucose, or sucrose. Corn syrup produced more than the individual sugars, an effect not merely due to the presence of glucose and maltose together. Yeast type markedly affects the production of volatile substances in these systems. The formation of individual volatile substances in malt and adjunct worts is influenced by agitation and yeast concentrations, different volatiles behaving differently according to the conditions used.