Main ester substances in beer and their effects on their contents

Esters are one of the important components that affect beer flavor. In a certain concentration range, esters can significantly improve the flavor of beer, but beyond this range, the beer will produce unpleasant odor.Generally speaking, the ratio of alcohol and ester in high quality beer should be controlled in 3-4.1

There are more than 50 kinds of esters in beer, and the main ester substances that affect the flavor of beer are ethyl acetate, isoamyl acetate, ethyl hexanoate, etc.

 One:Major ester substances in beer 

1.Ethyl acetate
When the ethyl acetate content in beer is low, the floral and mellow fragrance are stronger, and the overall aroma is not harmonious. When the concentration is controlled between 15mg/kg and 25mg/kg, the beer has the purest flavor.

2. Isoamyl acetate
When the content of isoamyl acetate was low, the beer was more mellow. On the high side, ester flavor and solvent flavor will be enhanced.
Generally, beer quality is best when the concentration of isoamyl acetate is controlled between 1mg/kg and 2mg/kg.

3. Ethyl caproate

When the content of ethyl caproate was low, the fragrance of wine was rich, and the wine body fragrance was not soft enough. On the high side, the wine aroma is too strong, the wine fragrance is reduced, so as to close to the liquor aroma. In general, controlling the concentration of ethyl caproate between 0.1mg/kg and 0.25mg/kg can make the best beer flavor.

 Two.Factors affecting the content of esters in beer 

1.Yeast species and addition amount

The formation of esters is related to the genetic characteristics of yeast. The fermentation metabolites of yeast with different fermentability are very different. The metabolic process of yeast with strong activity and healthy signs is beneficial to the synthesis of acyl coenzyme α and the generation of ester substances.

Under the same wort conditions and fermentation conditions, the more yeast addition, the lower the multiplication times of yeast, which can alleviate the competition of fatty acid synthesis and ester synthesis on acyl coenzyme A, resulting in enhanced ester synthesis and increased ester content.

2.Composition and concentration of wort

The ratio of carbon to nitrogen in wort should be controlled at an appropriate level. If the content of carbon is only increased or the content of nitrogen is decreased, the synthesis of some respiratory enzymes will be inhibited, leading to the weakening of the tristridium acid cycle, thus inhibiting the generation of ester. Therefore, fatty acid content in wort should be controlled at an appropriate level. When fatty acid content is low, yeast will consume a large amount of acetyl-CoA, which is used to synthesize fatty acids, thus reducing the production of esters.

Theoretically, the higher the wort concentration, the more esters are produced. The wort below 12 baume degree generally does not have the problem of excessive ester amount during fermentation, but if the wort concentration exceeds 15 baume degree, the yeast proliferation will be significantly inhibited due to the increase of metabolites, especially ethanol content. At this point, even though the dissolved oxygen and inoculation amount of wort also increase proportionally, the yeast does not increase proportionally with the increase in concentration, resulting in a decrease in fatty acid synthesis and an increase in ester production. Therefore, the high concentration diluted beer has higher ester content than the beer fermented with the same concentration, and the possibility of beer flavor defects is higher.

3. Fermentation temperature and method
High temperature fermentation was beneficial to the generation of esters. When the fermentation temperature increased from 12.5℃ to 25℃, the concentration of ethyl acetate and isoamyl acetate increased by 60% and 30% respectively.
The temperature of the above fermentation was higher than that of the below fermentation, the inoculation amount was lower than that of the below fermentation, but the ester content was higher than that of the below fermentation.
Pressurized closed fermentation can increase the content of saturated carbon dioxide in the liquor, inhibit the growth of active yeast, and thus benefit the generation of ester substances. The content of esters in fermentation byproducts can be increased by stirring fermentation.

 Three.Ester volume control measures 

1. If the open large tank is used for fermentation, the temperature of wort in different parts of the fermentation tank can be controlled to control the convection intensity of wort. When the convection intensity of wort decreased, the glucose lowering rate would decrease, and the volatile ester content would increase accordingly.
2. Keep the wort pH between 4.8 and 5.2.
3. Increase the wort concentration, such as 15 Baume or above.

4. Appropriately reduce the wort oxygenation level, which can be controlled within 6mg/ L-8mg/L.
5. Improve the inoculation amount of yeast appropriately. For wort of 15 baume, the number of yeast cells could be controlled between 15 million /ml and 20 million /ml.
6. Pressurized fermentation, improve the main fermentation temperature, improve the generation of ester substances.

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