From the HBD Archive
Subject: Re: high-temp ferment
Date: 1992-07-21 15:08:00 GMT

Rick asks:
>What sort of off-flavors are caused by high-temp fermentations?

High-temperature fermentations cause an increase in the production
esters, a slight increase in the risk of bacteria reaching levels
of significance, an increase in the production of diacetyl and an
increase in the production of fusel (higher) alcohols. The esters,
diacetyl and fusel alcohols, are not necessarily off-flavors unless
they are produced in such large quantities that they are distracting
or inapropriate for style (such as low-to-mid gravity lagers). Note
that "high-temperature" is relative -- for an ale, temperatures over
75F are usually considered "high" whereas for lagers, temps over 50F
are usually considered "high." Also, nothing starts suddenly at a
particular temperature, it's all a continium.

On a related note: if your yeast has a tendancy to create phenolics
(like Munton & Fison's Muntona yeast), it will create a more the higher
the fermentation temperature.

One factor that should also be addressed is that our brewing environment
may be different during warmer months: doors opening more often, open
windows, higher humidity (great for mold production), higher concentrarions
of wild yeasts as well as bacteria in the air, and warmer tapwater
(resulting in slower chilling if you use a tapwater-powered chiller).
Therefore, sanitation during warmer periods is much more important and
off-flavors can often be traced to problems in the environment.


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