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The objective of this study was to evaluate the usefulness of mixed cultures of microorganisms for the production of sour beers, as an alternative to low-alcohol beer beverages. The tests included the generation and evaluation of top-fermented beers produced with yeast and lactic acid bacteria and assess the impact of different carbohydrate sources for bottle conditioning on the sensoric features of the beer.
In the first stage of the study wort has been prepared with an extract of 7.3 wt.%, Which was pitched using Safale US-05 yeast and Lactobacillus brevis or Lactobacillus delbrueckii bacteria. The pitch was added at the beginning of a secondary fermentation, or during primary fermentation. Control sample consisted of beer pitched with yeast US-05 and beer made with commercial strain S. cerevisiae and Lactobacillus. In total, six variants were prepared. After the primary fermentation, secondary fermentation and conditioning alcohol content, extract, attenuation, carbohydrate profile, acidity of the beer was assessed, among others. Sensoric evaluation of the beer was carried out using a 50-point grading scale with the following attributes: aroma, color, taste, mouthfeel, bitterness, head quality. On the basis of the instrumental and sensoric evaluation, variants using the culture of the US-05 yeast and the mixed culture of yeast US-05 and bacteria Lb. delbrueckii added prior to secondary fermentation were selected for the second stage of the study. After secondary fermentation both variants were bottle-conditioned using 5 different additions: white sugar, unrefined cane sugar, malt extract, heather honey, and cherry syrup. After secondary fermentation and maturing similar evaluation as in the first stage was performed.
Based on the results, it was found that yeast and lactic acid bacteria are useful for production of light, sour top-fermenting beers. Produced beer was characterized by features typical to this type of beer: sour, refreshing taste, 3.3 - 3.8% alcohol by volume content. One distinctive variant was a mixed culture of Safale US-05 yeast and Lactobacillus delbrueckii. The best moment for inoculation of bacteria proved to be the beginning of secondary fermentation. Among the additives used for bottle-conditioning cherry syrup stood out, beer with this addition was the highest rated one according to a panel of tasters.