8 - Fermentation
The reactions that
take place during the conditioning phase are primarily a function of
the yeast. The vigorous attenuation stage is over, the majority of
the wort sugars have been converted to alcohol, and a lot of the yeast
cells are going dormant - but most are still active.
Phase allows for the slow reduction of the remaining fermentables.
The yeast have eaten most all of the easily fermentable sugars and
now start to turn their attention elsewhere. The yeast start to work
on the heavier sugars like maltotriose. Also, the yeast clean up some
of the byproducts they produced during the fast-paced primary phase.
But this stage has its dark side too.
conditions, the dormant yeast on the bottom of the fermentor begin dying
and excreting more amino and fatty acids. Leaving the post-primary
beer on the trub and yeast cake for too long (more than about six
weeks) will tend to result in soapy and/or meaty (ham-like) flavors
becoming evident. This autolysis of the yeast used to be more common
when homebrewing 20 years ago, but rarely happens nowadays due to
better yeast handling practices at home brewing supply shops and
better yeast quality overall.
Leaving an ale
beer in the primary fermentor for a total of 2-3 weeks versus one
when using single stage fermentation (i.e. not using a secondary
fermentor) will provide time for the conditioning reactions and
improve the finished beer. The extra time will also let more sediment
settle out before bottling, resulting in a clearer beer and easier
As a general rule,
do not rack the beer to a secondary fermenter unless you are
conducting a secondary fermentation with new fermentables, such as
fruit or are souring a beer by adding a bacterial culture. The risk
of oxidation and staling of the beer is greater than the risk of
autolysis from the beer sitting on the yeast until it is time to
bottle or keg it.