Function: turn/ferment sugars to alcohol and carbon dioxide
There's 2 main microbes:
Saccharomyces cerveisiae or ale yeast, and Saccharomyces pastorianus or lager yeast.
(Brettanomyces bruxellensis, third type of yeast in lambic)
Beer maverick database
Checking the pH of yeast before repitching it into the wort is recommended. A tired yeast slurry will have a higher than normal pH [>4.5] , eg 3 to 4, due to cytoplasm released by autolysed yeast. Healthy yeast will respond positively to clean, cold, oxygenated wort with adequate nutrients and no competition.
Grow yeast in lab YouTube
Yeast metabolises sugar from wort, producing alcohol and carbon dioxide, thereby turning wort into beer.
It ferments beer and influences its flavour profile, however, there must be no oxygen present.
In the presence of oxygen, yeast multiplies which is important for propagation and the baking industry. This can spoil the long-term stability of beer flavour and clarity.
When is oxygen is required in the brewing process?
New yeast is required from time to time as the yeast loses the ability to produce a good beer. That’s why you need a yeast propagation plant.
During propagation the yeast call is in respiration mode, which means uptake of oxygen. This means the yeast cell prefers to breathe rather than consuming sugars.
During the fermentation mode the yeast cell consumes 14 times for sugar in order to obtain the same amount of energy, that’s why yeast growth is about 10 times greater under respiration than fermentation
Pasture effect and crabtree effect
Native yeast on grapes:
Rhodotorula
Apiculate (lemon shaped) yeast Kloeckera apiculata
Hansenia uvarum - most common
Common brands:
Lavlin
Red star
Vinter's Harvest
Fermentis. For lager, s-23 more fruity than w34/70
Liquid yeast:
White Labs
Wyeast
Reference :
Autolysis factors like temperature, pH, nutrient availability, and oxygen levels can influence the rate of autolysis.
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