The main factors affecting the ester content

Craft beer is not blindly pursuing new, strange, special and different bottles, but should also focus on the stability of beer quality and the consistency of taste. Among them, the body esters have a weak aroma, uncoordinated and rough taste, etc., which greatly reduces the quality of beer. The content of ester in beer depends on the original wort concentration and beer variety. Generally, in the upper fermented beer, the ester content can be as high as 80 mg/L; in the lower fermented beer, the ester content is lower. Appropriate amount of ester content in beer can make the beer aroma harmonious and full; but too high ester content will cause unpleasant aroma or abnormal aroma to beer.

Most of the volatile esters in beer are formed during the main fermentation. The formation of esters is related to the growth of yeast and the metabolism of fatty acids. A small amount of esters can also be generated by esterification of higher alcohols. Esters are mainly produced during the vigorous fermentation period of yeast, and only slightly increase in post-fermentation of beer. The content of esters increased with increasing wort and ethanol concentrations. The amount of increase in the post-ripening stage depends on the post-fermentation, and if the post-fermentation period is longer, the ester content can be increased.

The main factors affecting the ester content:

№ 01 Yeast species 

Yeast species is the primary factor affecting the ester content in beer. The activity and production of acyl-CoA in the cells of different strains are different, so the ability to generate esters is also different. The same yeast species has different ability to generate esters due to different activities. Yeasts with strong growth and fermentation activities will metabolize to generate more ester acyl-CoA, thereby forming more esters. In addition, the synthesis of esters is related to the genetic characteristics of yeast, and the genetic characteristics of esters produced by different strains of the same species are also significantly different.

№ 02 Wort concentration 

Theoretically, the higher the wort concentration, the more esters are produced. Wort below 12oP generally does not have the problem of excessive ester content during fermentation, but if the wort concentration exceeds 15oP, yeast proliferation will be significantly inhibited due to the increase of metabolites, especially ethanol content. At this time, even if the dissolved oxygen of the wort and the amount of inoculum increase proportionally, the yeast will not increase in proportion to the increase in concentration, resulting in a decrease in the synthesis of fatty acids and an increase in the production of esters. Therefore, high-concentration diluted beer has higher ester content than beer fermented at the same concentration.

№ 03 Fermentation temperature 

High temperature fermentation is conducive to the formation of esters, mainly due to the following two aspects: First, the temperature in the main fermentation period is high, the fermentation is vigorous, and the yeast accumulates more energy during the hypoglycemic process, which enhances the activity of ester acyl-CoA, Thereby, the formation of esters is promoted; secondly, the temperature in the main fermentation period is high, the fluidity of the yeast cell membrane is enhanced, and the permeability is improved, thereby promoting the exudation of intracellular esters and increasing the ester content in the beer. The fermentation temperature was increased from 12.5°C to 25°C, the concentration of ethyl acetate was increased by 60%, and the isoamyl acetate was increased by 30%.

№ 04 Fermentation pressure 

The amount of esters produced is related to the pressure during fermentation. The higher the pressure, the more CO2 in the beer, inhibiting the growth of the yeast, thereby preventing the formation of low-chain volatile esters (such as ethyl acetate), and higher carbon-chain esters (such as ethyl heptanoate) will increase.

№ 05 Wort composition 

The ratio of amino acids to fermentable sugars in wort affects ester formation. Ester formation is correspondingly reduced if amino acids are high and proliferate under aerobic conditions; the same is true for fermentable sugars.

№ 06 Aeration and oxygenation 

The growth and reproduction of yeast has a great relationship with the oxygenation of wort, which also affects the production of esters. The less amount of ventilation and oxygenation, the more esters are generated; the more the amount of ventilation and oxygenation, the less esters are generated.

№ 07 Beer storage time 

During long-term wine storage, due to the alcohols and acids produced in the fermentation process, the ester content in the beer can be slightly increased by a simple esterification reaction during the storage process. However, because this simple esterification reaction is very slow, it can only be detected when the wine is stored for about 3 to 6 months. For example, when stored for more than 3 months, the content of ethyl acetate and isoamyl acetate will increase by about 10%.

№ 08 Unsaturated fatty acids 

Unsaturated fatty acids in wort directly inhibit the activity of ester synthase, thereby affecting ester synthesis.

№ 09 pH value

 The pH value of the fermentation broth mainly affects the esterase. When the pH value is 4.5~6.5, it is beneficial to the esterase to catalyze the synthesis of ester; when the pH value is less than 4.5 or greater than 7.5, the esterase will decompose the ester.

№ 10 Yeast autolysis 

Due to some synthetic high-carbon chain esters (such as ethyl fusate) in yeast cells, when yeast is autolyzed, the cell membrane is ruptured and released, thereby increasing the content of beer esters, but these esters are not. Popular with everyone.

№ 11 Process Measures 

All measures to accelerate yeast reproduction will reduce ester formation.