From the HBD Archive
From: Conn Copas <>
Subject: Re : blow-off vs trub
Date: 1992-02-28 13:38:13 GMT

Reading the post on scientific and statistical methods prompted me to think
that there are two quite distinct claims being made about the effects of trub.
The first is, that because trub is largely a tannin-protein precipitate,
contact with the brew may dissolve some of the tannin and produce astringent
flavours. This effect is presumably what those who have tasted blow-off have
detected, although it is often mislabelled as having something to do with
'hop resin'. The second claim is that yeast will extract oxygen from the trub
and in the process produce more fusel oil, which at low levels can be
interesting, but at higher levels tastes solvent-like and possibly harsh.

So here is one suggestion for an (incomplete) experimental design. Take some
trub and strain it. Dry it roughly by pressing between paper towel. Now place
it in an appropriate amount of water, preferably acidified and fortified with
pure alcohol to obtain a beer-strength mixture. Let sit for a period around
2 weeks, maybe with some agitating, then note whether anything has dissolved.

Incidentally, I understand that some breweries actually employ tannin as a
clarifying agent. I've demonstrated this to myself at home when making yeast
starters with malt extract. Adding a pinch of grape tannin (reputedly
equivalent to tannic acid) causes the wort to drop star bright without
ever being brought to the boil. It also results in a darker wort and the most
evil looking trub one is ever likely to encounter. Presumably, the breweries
then precipitate the dissolved tannin out with something else like gelatine
or Polyclar. Just to complicate the issue, tannin is also regarded as a haze
precursor, so my chemical musings cease at this point.

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