Collaborative study on yeast activity, gas production (AACC Method 89-01)

Abstract

A method of the American Association of Cereal Chemists (AACC) for determining yeast activity (gas production) was tested in a collaborative study involving five laboratories. Samples of three different manufacturers for each of three yeast types (three active dry yeasts, three compressed yeasts, and three instant active dry yeasts) were duplicated and tested in three dough formulations mainly characterized by their sugar content: lean dough (0%), straight dough (8%) and sweet dough (20%). Using the Risograph, gas production from yeasted dough was measured as total volume of gas evolved after 90 min then transformed to volume of gas per hour per gram of yeast solids. Within each yeast type, results showed that AACC Method 89-01 differentiated among yeast samples from different commercial sources. Within each laboratory, best repeatability was obtained with both lean and straight dough formulations (coefficient of variation lower than 5%); most results with sweet doughs were less repeatable giving coefficients of variation up to 15%. Inter-lab reproducibility of the method was not considered very good. Recommendations are presented to improve the probability with which statistical tests correctly detect differences between labs means.