This is the step where yeast our wonderful little minions turn a hop flavored sugary solution into beer and it’s an important step. Yeast don’t just make alcohol they produce many of the substances that give the beer its flavor. The contribution of the yeast to the flavor varies hugely, lager yeasts add little flavor were as the flavor of some Belgian beers is almost totally dependent on the yeast used and the temperature it ferments at.
Points of note :-
Like all living things yeast needs food and some trace elements both of which it will usually get from the wort.
- It’s important to choose the right yeast as it affects the flavor.
- Temperature control is important and for some beers it’s critical.
When yeast is added to the wort in the fermenter it starts to reproduce, the number cells grow and during this phase of the fermentation they need Oxygen.
Although it’s usual to talk about stages during a fermentation, growth stage and so on the stages are not totally separate they just represent what the vast majority of cells are doing at that time.
This should be done just prior to pitching the yeast and like most things brew related there are lots of ways to do it.
The ultimate method is to pass pure oxygen through a tube down to a 5 micron air stone at the bottom of the fermenter.
For that you need an Oxygen cylinder, a regulator, some tubing and the airstone.
I sometimes use a fish tank air pump to push air through a sterile filter and an airstone, this method works well but like the other airstone procedure is slightly harder to keep sanitary than simply splashing the wort so oxygen dissolves into it.
The commonest procedure, it has many variations, is to spin a sanitized spoon or paddle with a power drill and use it to whip the worth up until the foam is near the top of the fermentation vessel.
If the wort has a High specific gravity (SG) for instance over 1.070 or you’re starting a lager fermentation the yeast will want more oxygen than you’re going to get into the solution unless you have used oxygen. Most of the time you will get away with it but it is better to wait 4 or 5 hr and whip up or aerate the wort again.
In the past it was common for HomeBrewers mentally at least split the fermentation into primary and secondary stages. Often the beer would be transferred to a a new fermenter at the end of the primary stage.
Thee are problems with this, it increases the risk of oxidation and the risk of contamination. In addition those stages don’t really exist, there is just the fermentation and if it is done properly will be over well before the sediment at the bottom of the fermenter can be detrimental.