Comparing the efficiency of applying yeast of different generations in high gravity brewing

Abstract

When fermenting beer, in addition to the formation of basic, secondary, and by-products, which largely determine the taste and aroma of the beverage, yeast is accumulated. Such yeasts can be reused in subsequent serial repitching, which allows cost savings compared to yeast cultivated for each fermentation. This paper investigates the influence of yeast generation on the progress of the wort fermentation process and the quality of beer obtained, specifically in high gravity brewing. It was established that the increase in the number of yeast generation in the range from the first to the fourth generation causes a slight acceleration of the fermentation process of high-gravity wort, while at higher values of the fermentation generation number it slows down. Yeasts secreted after six or four serial wort fermentations with a gravity of 15 °P/18 °P, respectively, have a good physiological state and can be reused. The yeast generation number does not significantly affect ethanol content and sensory beer quality indicators. However, the use of yeast of the seventh and eighth generation causes a slight increase in the pH and color of high gravity beer, the appearance in the aroma of noticeable extraneous shades ‒ yeast tone, tone of young beer. As wort gravity increases, the number of yeast re-use cycles decreases, which is a consequence of the influence of various stress factors, specifically high osmotic pressure, and increased ethanol levels. Therefore, for the fermentation of wort with a gravity of 15 °P, it is recommended to use yeast up to five generations, for 18 °P wort ‒ to four generations. To obtain beer with appropriate physicochemical parameters and high sensory evaluation in high gravity brewing technology, it is advisable to ferment wort with a gravity of 15 °P with yeast for up to five generations.