The effect of fermentation on beer flavor

As a brewer who wants to start a brewery, it is important to understand the impact of fermentation on the flavor of the beer. Most brewers know that fermentation temperature affects the aroma of beer. Through the fermentation of different yeasts under different environmental conditions, rich fermentation flavors are produced, such as esters, phenols, and diacetyl, ethanol, and higher alcohols that bring peculiar flavors. Different combinations bring completely different flavors and affect the quality of the beer. Beer today presents a rich variety of aromas and flavors, and the wrong fermentation broth can ruin the beer and leave the beer full of off-flavors.

Aromas, we look for other sources of flavor substances to see if we can promote fermentation to produce the flavor we want.

Control Esters

Esters are a flavoring substance produced during fermentation. Esters are also common in everyday life, and you can find them in everything from essential oils to candy.

Types Of Esters In Beer

Esters play an important role in the taste and aroma of beer, and the following are common terms used in the home or commercial brewing：

• Isoamyl acetate – ripe banana flavor, when the content of isoamyl acetate is low, the mellow flavor of the beer is stronger; when it is high, the ester flavor and solvent flavor are enhanced. When the concentration is controlled at 1mg/kg-2mg/kg, the quality of the beer is the best.

• Ethyl acetate – Nail polish remover smell (solvent smell) at higher levels. When the ethyl acetate content in beer is low, the hop aroma and mellow aroma are strong, and the aroma is not harmonious. Control its concentration between 15mg/kg-25mg/kg, the aroma of the beer is the purest.

• Ethyl Caproate – Pear, Apple, Pineapple flavors. When the content is low, the aroma of hops is strong, and the aroma of the wine body is not soft enough; when the content is too high, the aroma of the wine is too strong, and the aroma of hops is reduced, which is close to the aroma of liquor. Generally, the concentration is controlled between 0.1mg/kg and 0.25mg/kg. Now, the aroma of the beer is the best.

• Ethyl Butyrate – Tropical Fruit Flavor

• Ethyl Caprylate – Apricot, Pineapple Flavor

The Link Between Beer Style And Esters

Esters come in many varieties, good and bad, and can create a flavor stack in beer. So, different types of esters provide different styles of beer. The classification of beer styles in the modern craft brewing industry is based on the type of brewer’s yeast. Brewers in the United States and most other regions are accustomed to referring to beers that use top-fermenting yeast as Ales, and beers that use bottom-fermented yeast are called Lagers. To be clear, it is the yeast (not the malt recipe) that shapes the ester aroma, and a certain type of yeast is used to ferment a certain style of beer. The German wheat yeast produces a banana aroma. In British traditional beers and cloudy IPAs, English yeasts bring fruity esters.

Factors Influencing The Formation Of Esters

The beer fermentation temperature contributes to the specific type of ester aroma in the beer. Fermentation at higher temperatures generally increases esters in the finished beer, lower temperatures tend to reduce ester formation. Fermentation temperature plays a very important role in the production of ester aroma in beer. Thus, to control the content and types of esters in beer, the key is to select the yeast species and control the fermentation temperature.

Low-temperature fermentation is believed to produce beer with improved taste and aroma as well as high ethanol and beer productivity. To save energy, space, and time, breweries use high specific gravity wort and ferment it at higher temperatures. The correct choice of process temperature, especially in the initial stages of fermentation, is crucial for the rapid propagation of yeast.

Fermentation Vessel

The structure and morphology of the fermenter tank the formation of ester aromas, with taller fermenters producing fewer ester aromas than stocky fermenters. This is because of the higher hydrostatic pressure and more dissolved carbon dioxide in the lanky fermenter, which inhibits the formation of esters. Pressurized and airtight fermentation can increase the content of saturated carbon dioxide in the wine, inhibit the growth of active yeast, and thus help the formation of esters. Stirring fermentation can increase the content of esters in fermentation by-products.

Yeast Species And Addition Amount

The formation of esters is related to the genetic characteristics of yeast. Yeasts with different fermenting powers have very different fermentative metabolites. Yeast with strong vitality and healthy signs, the metabolic process is conducive to the synthesis of acyl-CoA, which is conducive to the formation of esters.

Wort Composition And Concentration

Under the same wort conditions and fermentation conditions, the more yeast added, the smaller the yeast multiplication factor, thus alleviating the competition between fatty acid synthesis and ester synthesis for acyl-CoA, resulting in enhanced ester synthesis and increased ester content. , the higher the wort concentration, the more esters are produced. Yeast produces more esters, too much oxygen, and oil will keep yeast producing esters.

Now, even if the dissolved oxygen and the inoculum of the wort increase at the same time, 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. Thus, the high concentration of diluted beer has higher ester content than the beer fermented at the same concentration, and the possibility of beer flavor defects is higher.