Selection Of High Tolerance Brewer's Yeast And Optimization Of High Gravity Specialty Beer Brewing

Specialty beers,such as high gravity beers have wined the attention and affection of consumers with their mellow taste and innovative raw materials.However,high gravity beer(?15°P),especially very high gravity beer(?18°P)market is occupied by foreign brands.High gravity brewing is threatened by fermentation environment and processes,including high osmotic pressure,high alcohol content and lack of nutrition,etc.,which affect fermentation efficiency and quality of beers,hindering its development and production.The research firstly selected high tolerance Saccharomyces cerevisiae and optimized the process of malt saccharification,then further studied the fermentation process of very high gravity beer and developed two very high gravity specialty beers.Results are as follow:1.To obtain yeasts with high osmotic pressure and high alcohol resistance,atmospheric and room temperature plasma(ARTP)technology and a series of screening under high pressure medium were adopted on an industrial strain Saccharomyces cerevisiae.The results confirmed that the mutant strain SC16 had an excellent performance and flavor in very high gravity fermentation.Compared with the parent strain under 24°P fermentation,the descent rate of apparent extract of SC16 increased by 23.5%,the fermentation period reduced 2 d,the real attenuation increased by 10.0%,and the ethanol content increased by 8.1%.Fermentation performance remained stable after 10 continuous passages,which preliminarily confirmed that mutant strain SC16 was suitable for very high gravity beer brewing.2.Experiment was conducted to study the effects of different saccharification processes on malt hydrolysis and in the meantime optimize the saccarification processes.The optimum saccharification processes of malt were as follow:Protein rest for 1 hour at 50?,saccharify for 40 min at 65?then for 20 min at 72?,initial pH 5.0,glucoamylase addition 0.01%(V/V).The wort of 16°P produced under these conditions were fermented into alcohol,of which ethanol content reached to 6.5%vol and real attenuation reached to 75.3%.Compared with the original saccharification processes,the ethanol content and real attenuation respectively increased by 32.7%and 22.3%,which considerably improve the fermentability of wort.3.Single factor experiment and orthogonal test were conducted to study the effects of different fermentation processes on very high gravity fermentation performance and flavor and in the meantime optimize the fermentation processes.The optimum fermentation processes of very high gravity beer were as follow:Original wort concentration was 20°P,pitching rate was 5×10~7 cfu/m,primary fermentation temperature and time was respectively15?and 7 d,hop addition during wort boiling and fermentation was respectively 0.05%(W/V)and 0.009%(W/V).The beer produced under these conditions has a pure and strong body,with rich hop flavor,fresh malt and hop fragrance,of which ethanol content reached to9.5%vol and real attenuation reached to 70.0%.4.Based on the optimum processes of very high gravity fermentation,single factor and orthogonal test were conducted to study the effects of different fermentation processes and composition on green plum beer.The optimum formulas of green plum beer were as follow:Addition percentage and time of green plum juice was respectively 10%(V/V)and 3d after fermentation,hop addition during wort boiling was 0.05%(W/V),with no extra hop addition during the period of fermentation.The green plum beer produced under these conditions tasted soft and full-bodied,with typical flavor and fresh fragrance of green plum,of which ethanol content was 8.9%vol and real attenuation was 62.5%.