Foreign organisms in industrial yeasts are primarily obligate beer-spoilage bacteria (e.g. beer-spoilage lactobacilli and pediococci) and wild yeasts. In addition, the yeast should also be free of other accompanying organisms (e.g. wort bacteria, acetic acid bacteria, indicator bacteria). Yeast water is a suitable culture medium for detecting bacteria from the accompanying flora. There should not be any bacteria detected when analysing brewery yeast cultures with yeast water. This test is part of the yeast propagation test to ensure absolute freedom from foreign bacteria in a pure yeast culture.
Brewery yeast culture, pitching and harvest yeast as well as pure yeast.
Thermally extracted yeasts release their cell contents into the surrounding medium (= yeast water), which is then available for bacteria.