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.
Brewing yeasts
Analysis of yeasts for dead cells using propidium iodide in a cell counter.
Determination of the vitality of brewing yeasts
The acidification power is defined as the acidification of a solution of distilled water with a defined pH of 6.3 and a glucose concentration of 5 % at 25 °C by a yeast.
The pH curve is documented and serves as an indication of yeast vitality.
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.
Industrial yeasts from the brewing process.
Live, aerobic yeast cells possess dehydrogeneases which reduce the methylene blue absorbed into the cell to its colourless leuco form, giving the cells a pale blue colour. Dead or inactive cells lack dehydrogenase activity and turn an intense blue colour.
Foreign organisms in industrial yeasts are primarily obligate beer-spoilage organisms (gram-positive and gram-negative anaerobes) and wild yeasts.
Brewery yeast and purchased yeast
Dark-field microscopy of the sample with subsequent enrichment.