Alternative Measures of Yeast Vitality: Use of Cumulative Acidification Power and Conductance

Abstract

Two ideas are presented to increase the sensitivity of the acidification power test. The first deals with expressing yeast vitality as the cumulative proton absolute concentration change (designated as cumulative acidification power). This measure compensates for the logarithmic nature of the pH scale and for acidification curves exhibiting both an increase and decrease in pH during the test. The second idea deals with the use of an exogenous energy source closer to what the yeast normally encounters during fermentation. This is illustrated for pilot fermentations using yeasts that have been exposed predominantly to either glucose or maltose for 56 generations. Conductance is proposed as an alternative measure to pH and is shown to respond similarly to yeast history. All three measures (acidification power, cumulative acidification power, and conductance change) are shown to be significantly correlated in a collection of 43 comparative acidification runs.