After cooling the wort below 80 F, it’s time to innoculate it with your beer yeast.
This act is called pitching. Comes from days of old when they would actually walk
along the open fermenters and pitch the yeast like sowing seeds.
It is important to control the temperature during fermentation as it is an exothermic
process and produces heat. Run away fermentations produce all kinds of nasty flavor
compounds and a hot solventy beer. We don’t want that ! Also, higher order alcohols
can be produced at temps above 80 and these will give you a nasty headache or hangover.
Keep the fermenting beer as cool as reasonable for the yeast and style you are making.
For ales this means just at or below room temps ( ideally mid 60s ) while for lagers
we want a cold fermentation of 40-58 F.
Keep in mind that yeast are alive and like all living things they will start to acclimate
to their new environment after pitching. Depending on the strain, their health, the
amount of active yeast and the medium they are being introduced to will all determine
just how they behave.
During the early stages the yeast will usually undergo a lag time. This is the period
after pitching that they are multiplying (respiration) and taking up sterols in the
wort to get ready for fermentation.
It can range from a couple hours to 24. The longer the lag, the more potential for
other rogue yeast or bacteria to get going in the wort and ruin the beer. A short
lag is prefered. It indicates things are fine and the little buggers are ready to
After the lag, the yeast start consuming the sugars. This is fermentation. They start
with the simple sugars first, the easy ones to pass through their cell walls and
digest producing CO2 and alcohol as waste along with many other compounds that are
important to the finished beer. Depending on beer style, amount of yeast, temps,
etc will determine how long this may take. As a rule of thumb let’s assume a standard
brown ale. Dry yeast usually ferments a beer in 12 to 32 hours for an ale and if
using a pitchable liquid yeast pack can take a few days. Lagers take longer because
they ferment at a much colder temperature and is the reason why lagers taste crisp,
clean and without any fruitiness ( esters ) that may be imparted in a ale. It is
not unusual for lagers to take a week or more to ferment.
At the end of fermentation, when most the sugars that can be consumed have been,
the yeast will clump together and start falling to the bottom. This is called flocculation.
This trait is noted with most yeast strains so as to pick an appropriate one to match
the beer being made. High flocculation means the yeast tend to clear well and sometimes
early while low flocculation means they tend the hang around in the beer. Such an
example would be hefeweizen which is cloudy due to the strains of yeast used.