The relationship between beer yeast and beer quality
In beer production, yeast cells are not the final product, but they are very important to the quality of the final product. A series of complex biochemical reactions during the fermentation process are caused by the nutritional metabolism of yeast. Therefore, yeast plays an important role in beer production and fermentation quality, as well as the physical and chemical properties of beer. Both performance and flavor typicality have an important impact.
Yeast and fermentation speed
The fermentation speed of yeast is one of the important indicators of beer production. Under certain technological conditions, the yeast can successfully ferment the wort, thus ensuring the quality of the beer. At the same time, on the premise of ensuring fermentation quality, giving full play to the inherent potential of yeast cells can accelerate the production cycle and improve production capacity. The factors that affect yeast fermentation speed mainly include the following aspects:
Yeast concentration
When the yeast cells are fully stirred and evenly distributed in the fermentation broth, the fermentation speed is directly proportional to the concentration of yeast, such as:
The inoculum volume is 0.6L/hl, and the fermentation days are 9 days;
The inoculation volume is 1.0L/hl, and the fermentation days are 7 days;
The inoculum volume is 2.0L/hl, and the fermentation days are 4 to 5 days;
Of course, there is no need to use an excessively high yeast inoculation amount in actual production, because too high an inoculation amount will easily cause the yeast to decline and the fermentation phenomenon will be difficult to control.
Yeast fermentation power
Fermentation power is used to measure the ability of yeast to ferment alcohol. It changes greatly due to the influence of the environment. For example, the storage conditions of the yeast and the attachments on the cell surface all have an impact on the fermentation power. The fermentation power of yeast is also different depending on the age and strain properties of the yeast. The protoplasmic toxins of yeast metabolites will also inhibit its fermentation ability. When the alcohol produced by fermentation exceeds 8.5%, fermentation will also be inhibited, reducing the fermentation power of the yeast.
Wort composition
The copper in the wort is absorbed and accumulated by the yeast to a certain extent, which will cause the yeast to decline and slow down the fermentation speed; the content of the assimilable nitrogen source in the wort also affects the fermentation speed. Generally, the fermentation power increases with the increase in nitrogen content. ;The most suitable pH value for yeast to ferment sugar in wort is 4~6. If it exceeds the range, it will affect the fermentation speed.
Fermentation temperature
Temperature will directly affect the reproduction and fermentation power of yeast, especially the lower yeast. Higher temperatures can speed up fermentation.
Yeast and fermentation
The fermentation degree of beer yeast reflects the fermentation of various sugars by the yeast. Normal brewer's yeast can ferment glucose, fructose, sucrose, maltose and maltotriose. Brewing different types of beer requires different degrees of fermentation. Some yeasts have a higher degree of fermentation, while some yeasts cannot ferment maltotriose and thus reduce the degree of fermentation.
Under some abnormal circumstances, if the fermentation degree of the yeast decreases, on the one hand, it means that the yeast may have mutated or been contaminated. On the other hand, the wort composition and fermentation conditions should be checked to see if they are appropriate. The fermentation degree determines the type and taste of beer. Generally, the fermentation degree of beer is controlled: the apparent fermentation degree is 65%~80%, and the real fermentation degree is 55%~70%. Generally speaking, beers with low fermentation degree are not mellow, but are sticky, greasy, and sweet, and their shelf life is also short; beers with high fermentation degree are mostly mellow and have the "body" of beer.
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