Esters in beer fermentation process of industrial control

Fermentation process, the flavor of saccharomyces cerevisiae to generate a large number of active substances, the flavor of active substances has six kinds: organic acids, higher alcohols, hydroxyl compounds, HanLiuFen, phenolic components and volatile esters. Although volatile esters is the flavor of active material of trace elements, it is the most important flavor active component. In the beer industry, volatile esters are concerned, because they can produce fruit, candy flavour, perfume, is the main body of beer flavor types of contributors. Esters generally have lower threshold flavor in beer. Because most of the ester produced by saccharomyces cerevisiae during fermentation and the concentration fluctuations around in their respective threshold, the secondary metabolites of small changes can produce great influence on sensory quality of beer. Therefore, understanding the ester formation mechanism in order to better control the final product level of ester, is also one of the goals of the industrialization. Ester synthesis biochemistry background has been thorough research, people found that ester formation speed depends on three factors: two of the substrate concentration ( Acetyl CoA and alcohol) , enzyme activity, Including the synthesis and hydrolysis activity) 。 Therefore, all factors affecting the substrate concentration and enzyme activity are likely to affect ester generated. There are two kinds of active ester flavor in beer, is a kind of acetic ester, ethyl is a kind of class. In these two kinds of ester, acetic ester ethyl acetate was the most extensive attention, because of its higher concentration, easier to detect, and its synthetic gene is reported in the first place. Relatively speaking, so far people know little about the generation of ethyl esters, only know that they have the pleasant apple smell. Recent progress has identified several synthetic their genes and describes its biochemical pathways. These active ester by fermentation in yeast cells to form, because is fat-soluble, ethyl ester chain fatty acid in the class ( MCFA ethyl ester） Can pass the cytoplasmic membrane diffusion to the fermentation medium. Acetic acid esters can be quickly and complete diffusion in the culture medium, and ethyl ester to transfer to the fermentation medium is dependent on their composition. With the increase of fatty acid chain length, the diffusion speed down sharply. Ethyl MCFA between yeast and beer distribution affected by the type of yeast. Raga (yeast Saccharomyces pastorianus） Keep more MCFA ethyl ester in the cell. And, ethyl MCFA on yeast and beer distribution between depends on temperature, low temperature, yeast cells to retain more ester, less conversely. Ester synthesis needs two substances: alcohol and acid. Esters can be formed by chemical reactions but esterification reaction speed slow enough to form a sufficient number of esters in beer. In 1962, the researchers found that esters by acyltransferase ( Or ester synthetase) Formed within the cells of the catalytic process. Response required from acyl coenzyme A ( CoA） Auxiliary substrate sulphur ester bond to provide energy. Is one of the most abundant acyl CoA acetyl CoA, it can not only through the formation of oxidative decarboxylation of pyruvic acid can also be directly under the action of ATP by acetic acid activation. The majority of the CoA of pyruvic acid by oxidative decarboxylation is formed, most of the others acetyl CoA through acyl CoA synthetase ( Fatty acid metabolism) By the catalysis of acyl im into free CoA. Modern beer industry to meet and need urgently to solve the question is: 1) high concentration fermentation ( Produce a disproportionate share of ethyl acetate and isoamyl acetate) ; (2) on a large scale application of cone bottom fermentation tank ( To reduce the generation of the ester) ; (3) production of low alcohol beer ( The lack of flavor substances) 。 There were many parameters influencing beer ester synthesis, there are a large number of literature to study the effect of ester of beer flavor level parameters. The factors influencing ester synthesis can be divided into three categories: yeast properties and composition of wort and fermentation conditions ( See table 6 - 1) 。 The company's web site: tranogroup. com