89 Yeast Methods​

89-01.01 Yeast Activity, Gas Production

The method determines the total gas production of yeast, expressed in ml, at standard barometric pressure over time. It permits comparison of gassing activity among various samples of yeast and provides a means to monitor yeast consistency. It is not intended to predict performance in the bakery because variations in formulation and processing conditions cannot be duplicated in the activity test method. The method is applicable to commercial yeasts, including compressed yeast (CY) with approximately 30% solids, active dry yeast (ADY) with approximately 92% solids, and, by using a slightly different testing procedure, instant dry yeast (IDY) with approximately 95% solids. High levels of sugar may significantlly affect yeast activity. Formulas containing 0, 8, and 20% sugar (flour basis) are provided. Dough formulations are calculated so that equal weights of dough contain equal weights of yeast solids (0.70 g of yeast solids per 100 g of dough).

Yeast activity in terms of gas production is greatly affected by variations in time, temperature, and ingredients. One approach to account for these sources of variation is to include a standard sample from a single lot of IDY, stored at 4° in a refrigerator. Several type of instruments can be used in this method, but comparison of results should be limited to data obtained from the same type of measuring device within the same laboratory.

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