Reduce High-class Beer Alcohol Content

The thesis researched systemically on the main factors that effects the amount of byproducts which beer yeast cells excrete during fermentation . The results showed that different pH values of acid water had great effect on saccharification of malt, and the saccharification was better at pH 5.0; that the quality of water also affected the saccharification in that acid water wich had bigger buffer capacity would be more favorable in malt saccharifying; that the use of hydrochloric acid (HA),phosphate acid (PA) and latic acid (LA) would cause increasing in the buffer capacity of wort ,and PA gave the biggest buffer capacity of wort which raised 1.5 times amount of that compared with HA ; that the buffer capacity of wort affected the yield of higher alcohols during beer fermentation as pH did, and the output of higher alcohols when beer fermentation used the wort saccharified in acid water concocted by PA or LA under the same conditions was higer than that by hydrochloric acid, and the wort by LA gave the biggest final quantity of higher alcohols; that excessive PA would cause blooming growth of yeast cell and significantly improve the amount of higher alcoholsin the beer on the contrary; that wort boiling was important to decreasing of buffer capacity of wort and caused about 30% reduction; that the quality of water, acid added and wort boiling were the main factors which effected the buffer capacity of wort on the condition that the main component of wot was given; that the common relationship between the buffering capacity of wort and the yield of higher alcohols in beer was that bigger buffer capacity caused more higher alcohols. The meaning of buffle capacity of wort to the beer fermantation was that the pH value of beer could be controlled by controlling the buffle capacity of wort during fermantation . Suitable buffle capacity of wort was optimized according to all the factors interrelated.On the breeding method of low higher alcohols yield and low diacetyl level yeast, this paper put forward an idea which would be used as a rule in yeast breeding when wild type mutant yeasts which grew at a moderate rate morphologically, whose LDH activity were higher than its original strains,would be firstly screened .After ultraviolet mutagensis(its fatality rate was 99.9%), isolated with lactic acid plate,wort -CaCO3 plate and colored by TTC upper layer plate, a mutain strain was obtained, which higher alcohols production was 30%or so lower than that of oringinal strain and Diacetyl level of final beer was 5%or so lower too,and further confirmed the feasibility of this breedingidea.This paper applied orthogonal design in fermentation conditions' optimizing. Some optimized conditions was primarily confirmed as pH6.0, a -aminonitrogen 140mg/L, inoculation amount 20%, soluble oxygen as the stationary cultivation 2 hr after high temperature sterilization, fermentation temperature 10 C. As a result,the amount of higher alcohols in final beer was 15% or so lower than that under the traditional ones.For the need of research, this paper also set up a method to detect the content of LAin beer and another one for the LDH activity of beer yeast, and checked the content of LA and LDH activity of beeryeast during main fermantation.