Search: Wild Yeast

Thermally extracted yeasts release their cell contents into the surrounding medium (= yeast water), which is then available for bacteria.

Analysis of yeasts for dead cells using propidium iodide in a cell counter.

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.

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.

Aside from evaluating the criteria flavor, fullness, liveliness and bitterness, based on the DLG Quality Assessment for Beer (refer to S.590.53.700 Einzelprobenprüfung zur Qualitätskontrolle von Bier - DLG-Prüfschema für Bier), the additional gustatory impressions of the four prevailing Southern German wheat beer styles are examined more closely. Thus, the sensory intensity and quality of the estery, phenolic, yeasty and malty notes in these beers can be assessed. Estery beers exhibit an evident fruitiness, of which the banana-like aroma of isoamyl acetate is the most prevalent. Wheat beers of the phenolic variety impart a clove-like impression, primarily due to 4-vinyl guaiacol, which at higher concentrations can be perceived as medicinal. Yeasty beers can exhibit a wide range of flavor-active fermentation by-products; however, old yeast and sulfur notes tend to dominate. Except of course for malty notes, wheat beers of a more malty or neutral character do not usually possess a distinctive aroma. The criteria are evaluated on a five-point scale, with 5 considered to be “pure” and 1 as “exhibiting major faults”. Scores are also possible in half-point steps.

Preliminary microscopic analysis for obligate beer-spoilage organisms and wild yeasts with subsequent enrichment.