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Background This study is concentrated on an improvement of beer fermentation under very high gravity (VHG) conditions using immobilised bottom-fermenting yeast strain Saccharomyces cerevisiae.
Methods. The yeast cells, free or immobilised in calcium alginate, calcium pectate, k-carrageenan, agar or DEAEcellulose, were used for batch wort fermentation of different gravity - 12 to 30% (w/w). A significant increase of fermentation rate of VHG wort for yeasts entrapped in calcium pectate or calcium alginate in comparison to free cells was observed.
Results. The specific rates of saccharides utilisation and ethanol production of free yeasts and yeasts immobilised on DEAF-cellulose were very similar at all concentrations of wort and were reduced, as compared to yeasts immobilised in other carriers studied. Ethanol toxicity affects mainly the cell membrane by altering the lipid bilayer and thus weakening the structure. The yeast responds by increasing its intracellular contents as well as the unsaturated fatty acid concentration. Increasing concentration of produced ethanol decreased the relative percentage of saturated fatty acids, especially palmitic (16:0) and stearic (18:0), more in free and on DEAF-cellulose immobilised cells than in yeast immobilised by entrapment.
Conclusions. The results confirm that immobilisation protects the microbial cells against the possible toxic effect of substrates or products whereby entrapment in gel appeared to be more favourable than adsorption. If
the gel matrix contained calcium cations, the ethanol tolerance was even more improved.
KEY WORDs: Saccharomyces - Beer - Calcium pectate - Calcium alginate - K-Carrageenan - DEAF-cellulose - Very high gravity brewing.
Similar as in distillers and fuel alcohol manufacturers, novel, very high gravity fermentation technology may prove to be a major innovation in brewing industry. Traditional (normal gravity) brewing is done with worts...