Evaluation of different yeast strains on the quality of beer produced from malted proso millet (Panicum miliaceum L.)

In order to investigate the influence of temperature on pH, alcohol production, carbohydrate profile and aroma compounds, a variety of top-fermenting yeast strains were used to ferment wort obtained from proso millet malt. Champagne (Saccharomycesbayanus), altbier, kölsch and ale (Saccharomycescerevisiae), as well as Brettanomyces bruxellensis were used in two isothermal (12 and 18°C) fermentation trials. During the fermentation, changes in pH, extract conversion and the monosaccharide profile were monitored. After 2 weeks of storage, the levels of higher alcohols and esters were also measured in the finished beers. In many cases, a strong resemblance in the behaviour of the selected strains to Saccharomyces was observed during the fermentation. All other influencing fermenting parameters like pitching rate, yeast generation, fermenting vessels geometry, amount of assimilable nitrogen, yeast nutrients, oxygen and CO₂ content and the sugar content were the same for all trials regardless of the yeast applied. However, at higher temperatures Brettanomyces showed more rapid rates of sugar conversion. Concerning the development of aroma components, no uniform picture was evident in these trials, neither with respect to temperature dependence nor to what extent the incurred values are comparable to those already known for beers brewed using barley malt wort. The values for aliphatic alcohols obtained during experimentation, ranged from 23 to 267 μg/L, and the sum of aromatic alcohols, from 2,437 to 11,844 μg/L. Values for ester content were recorded between 188 and 2,543 μg/L. Overall, wort produced using proso millet malt was found to be a substrate that lends itself to alcoholic fermentation, exhibiting a sufficient decrease in pH over the course of fermentation, as well as reasonable alcohol yield and a broad range of aroma components.