Foreign organisms in industrial yeasts are primarily obligate beer-spoilage organisms (gram-positive lactic acid bacteria such as lactobacilli and pediococci as well as gram-negative anaerobes) and wild yeasts. If there are traces of these viable or pre-damaged microorganisms in the yeast, they can irreversibly damage the beer in the further process.
Process samples that contain yeast
Anaerobic cultivation, dark-field microscopy of the sample.