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.
Foreign organisms in brewery yeasts are primarily obligate beer-spoilage organisms and wild yeasts. This method aims to detect wild yeasts in brewery yeast cultures.
Process samples containing yeast
Brewery yeast cultures cannot grow in the presence of more than 200 ppm copper sulphate (CuSO4) in a culture medium. The majority of wild yeasts are not inhibited by this concentration. This means that a universal yeast medium (e.g. YM) with the addition of 200 ppm CuSO4 can help detect the presence of wild yeasts in bottom- and top-fermenting brewery yeast cultures.
Brewing yeasts
Analysis of yeasts for dead cells using propidium iodide in a cell counter.
Cloudy Hefeweizen beer samples from the fermentation tank to the filled bottle.
Preliminary microscopic analysis for obligate beer-spoilage organisms and wild yeasts with subsequent enrichment.
Unfiltered, cloudy beer samples
Analysis of the microbiological status of green beer samples, in particular the presence of obligate beer-spoilage organisms and wild yeasts.
Cloudy beer samples with sediment
Microscopic examination of the sediment for obligate beer-spoilage organisms and wild yeasts by selective enrichment.