Secondary fermentation of cask ales

<editor's note>
From a post on the Home Brew Digest
</editor's note>

Date: Thu, 24 Oct 2002 17:37:32 +0100
From: Graham Stone 
Subject: RE: SECONDARY posting by Kevin

The issue about secondary fermentation is very confusing and badly written
in most homebrew books.  In fact, it confused the hell out of me for some
time!  Here's how I understand the terminology - it's not precise!  In a nut
shell, primary fermentation is an expression that generally refers to the
process of fermenting wort to a desired final or finishing gravity.  At his
point, you often have to do something to stop fermentation.  Commercially,
this is generally done by cooling the fermenting wort to about 12C over a
period of about 30 hours or more.  Sometimes the wort is racked into a clean
container so that it is removed from the bulk of the yeast.  The beer is
then left to stand in a conditioning tank for between 2 days and 2 weeks or
more (different breweries do things differently).  During this time, because
the yeast is not producing much CO2, it tends to sink to the bottom of the
vessel.  After this, the beer is racked into casks.  What's important at
this point is there there is an appropriate yeast count (ie cells per
litre).  Now, the expression Secondary Fermentation is what takes place in
the cask.  This results in the beer producing, ideally, about 1.5 volumes of
CO2 giving the finished beer a slight sparkle on the tongue - it shouldn't
be fizzy!  This sparkle on the tongue is called Condition.  Therefore, the
purpose of Secondary Fermentation is only to produce Condition and not, per
se, to drop the gravity of the beer any more than necessary (we allow about
0.5 degrees for Customs and Excise purposes).  It is generally at the point
of racking into casks that the beer is also fined with isinglass too
(although secondary finings are sometimes added to the conditioning tank
instead).

In our brewery, this is how we do most beers:

1.  Fermentation takes 2-3 days to get to the desired finishing gravity (say
1048 to 1012)
2.  Rack into clean FV and chill to 12C over 48hrs
3.  Rack into casks and store for at least 2 days, longer for stronger or
darker beers
4.  Transport to pub and stand in cellar at 12C for minimum of 2 days

After that, it's ready to drink!  So if we're desparate to try a new beer,
we could be drinking it 7-9 days after making it.  So Kevin's schedule of
several weeks is, in my opinion, rather lengthy for many recipes.  However,
there are some aspects to storage of casked beer you need to consider:

1.  Different yeasts produce differing quantities of acetaldehyde and other
unwanted by-products.  Acetaldehyde gives new beer a green apple taste
(acidic, tart, etc) and hence the expression Green Beer.  This abates in
time and is part of the maturation process.

2.  Bitterness abates slightly through time and hop/dark malt flavours
change too.  This in turn affects the malt/hop taste balance as well

3.  The longer you store the casked beer, the more condition it will acquire
(up to a point)

So, the length you store it for ought to be regarded as much a part of the
recipe as it is a part of the brewing process.  That is, I would dream of
serving a strong winter brew after only 9 days (this should probably have at
least 4 weeks or more) whereas a 100% pale ale recipe with moderate hop
levels would, with our yeast, drink beautifully!!

Graham Stone
www.portchesterbrewery.co.uk

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