Preliminary Study On Very High Gravity Brewing

With the maturing of high gravity brewing, very high gravity brewing was developed. This technology could reduce energy consumption, save labor force, and enhance equipment efficiency effectively. It was widely used overseas. In this paper, very high gravity brewing was studied from comparisons of yeast characteristics, raw material ratio, selection of nitrogen variety and fermentation conditions.Differences in fermentation characteristics including alcohol resistant capacity, osmotic pressure resistant capacity, flocculation capability, real attenuation, assimilative ration of free amino nitrogen (FAN) of ten yeast strains were compared. Fuzzy comprehensive evaluation was used to analyze the properties of 10 yeast strains. Through the characteristics quantification, the suitable strain (No.8) for very high gravity brewing was selected.In order to investigate the best composition of raw material and evaluation system of wort factors, the influences of three factors of very high gravity wort on brewing productivity were studied. Original extract, initial pH and percentage of corn syrup 2~3 factorial design of these factors was used. The results showed that the percentage of corn syrup had no influence on productivity whereas initial pH and initial wort concentration did. When pH and initial wort concentration values were 5.5 and 20°P, respectively, a higher productivity could be obtained. Under these conditions, the model predicted a productivity of 0.15g(/L·h). A productivity of 0.146g/(L·h) was observed under optimal conditions.According to the requirements of the brewing yeast metabolism, yeast food was added into wort as supplement of nitrogen. The effect of yeast food was studied according to FAN in wort. The effects of yeast food on acetyl content, higher alcohols content and the indices of the beer were studied. A kind of yeast food was selected which has reasonable amino acid spectrum. The optimal content of FAN in the very high gravity wort was 210 mg/L.By factorial methodology and analysis, the optimal fermentation conditions for higher productivity was as follows: main fermentation temperature 15℃, second fermentation temperature 12℃, inoculation rate 2.5×10~7 cell/mL. Successively, physical-chemical indices of beer and tasting degustation experimentation were carried out to compare the very high gravity brewing beer and normal gravity beer. The results showed that the main flavor of both beers were similar. Very high gravity brewed beer has reasonable proportion of alcohols to esters lower attenuation, lower color, higher non-biological stability, and stronger antioxidative ability.