1. Create “yeast taste” in beer
After yeast autolysis, a large quantity of intracellular compounds enters the beer, resulting in the creation of a distinct “yeast taste”. One representative compound is ethyl decanoate, and when its concentration exceeds 1.5 × 10-6 (1.5 ppm), it can cause a highly unpleasant sensation for individuals.
2. Exacerbate the astringency and bitterness of beer
The release of amino acids during yeast autolysis introduces various flavor compounds that intensify the bitterness of beer. This is commonly referred to as “bitter yeast”. Additionally, acidity levels are also increased, which diminishes the refreshing taste of beer.
3. Generate diacetyl odor
Following yeast autolysis, diacetyl and its precursor α-acetolactate enter the beer. Acetyl decarboxylase then produces diacetyl, causing an increase in its content in the beer, which may exceed the acceptable limit and result in the production of substandard products. This leads to loss of re-drinking.
4. Impact the stability of beer
Yeast autolysis leads to the breakdown of autolysase enzymes, resulting in the production of nitrogen-containing compounds of various molecular sizes. These compounds are difficult to remove during filtration, affecting the blending of beer and causing a loss of smoothness and gloss. Changes in pH value also disrupt the equilibrium of beer colloids, reducing its stability.
5. Foam interference
Nucleic acid compounds present in the yeast solution increase the total acid content in beer. Additionally, the release of proteolytic enzymes into the beer hydrolyzes the foaming proteins, leading to a disruption in foam formation and persistence.
6. Impact on beer acidity
Yeast increases the total acid content in beer through the release of nucleic acid compounds. Furthermore, protein compounds react with NaOH during acid-base titration, resulting in increased consumption of NaOH and an overall increase in the calculated acid content. The release of amino acids and proteins during yeast autolysis also alters the pH value of beer. The high isoelectric point of amino acids and proteins raises the pH value of beer. As beer has buffering capacity, the pH value does not change significantly and is not linear.
7. Effect on beer filtration performance
The macromolecules produced during beer autolysis can block the pore size of the filtration media, leading to filtration problems and increased dirt intake. Autolyzed yeast increases the viscosity of beer, impacting filtration efficiency and increasing filtration costs. Yeast autolysis is one of the key factors affecting beer filtration rate.