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	FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
		Digest Janitor: pbabcock at hbd.org


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Contents:
  RE: pre-boil oxidation [SEC=UNCLASSIFIED] ("Williams, Rowan")
  RE: decoctions [SEC=UNCLASSIFIED] ("Williams, Rowan")


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Date: Tue, 1 Dec 2009 12:27:34 +1100
From: "Williams, Rowan" <Rowan.Williams at ag.gov.au>
Subject: RE: pre-boil oxidation [SEC=UNCLASSIFIED]

Darrell, in HBD 5631 enquired about pre-boil oxidation...

I will leave it to others far better qualified than I to discuss
the chemical reactions involved, but my understanding is
that vigorous stirring and other such activities that disrupt
the mash surface may result in oxidation of compounds in
the mash that may promote earlier than anticipated stale
flavour notes.

It is commonly described as a wet cardboard flavour profile.

I dimly recall earlier discussions involving the interaction
between surface air and phenolics in the wort?

I understand HSA is mentioned in the context of handling
hot wort whereas pre-boil oxidation is a term that can
generally apply to both the mash and the wort derived prior
to the boil step commencing.

There are plenty of references to oxidation throughout the
archive....

Cheers,
Rowan
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Date: Tue, 1 Dec 2009 13:00:22 +1100
From: "Williams, Rowan" <Rowan.Williams at ag.gov.au>
Subject: RE: decoctions [SEC=UNCLASSIFIED]

Thanks to all those who kindly provided me with a lot of very
useful information on performing decoctions as part of the
quest to make authentic pilsners....

However it would be remiss of me not to share a very
useful data point that is often glossed over or indeed
overlooked, in many of the articles on decoction mashing
that I've read of late.

Decoction mashing is not just about heating up a portion of
the mash as quick as possible to boiling point and then tossing
it back into the main mash....it's about knowing what goes on
at each step and accounting for those complex interactions.

This is especially relevant if you decoct a proportion of the
mash that has not yet reached saccharification temps.

I understand that enzymatic conversion of starches happens
over a relatively broad temperature range, but we often refer
to fairly well defined optimal temperature bands for starch
conversion using alpha and beta amylase enzymes.  The
point here is that if you are decocting in order to bring the
mash up from an acid or protein or glucan rest, you should
ensure that the pulled mash that you're about to boil has
had an opportunity to rest at saccharification temps before
you boil that quantity of mash and thus denature the
enzymes in the pulled decoction.

In more practical terms, I want to raise my Czech pils mash
from a protein rest to a saccharification rest via decoction.
So, I will pull around a third of the mash, heat it in a pot on
the stove to achieve saccharification rest temps (approx
68C) in this instance, let it rest at that temp for around 20
mins and then heat it to a boil for a further 20 mins to
encourage the flavour positive attributes through
caramelization etc, before gently returning the decoction
to the main mash so as to bring the whole mash up to
saccharification rest temperature.
It goes without saying that the main mash has been
covered during this process and continued to sit at
protein rest temps during the decoction.

I suppose we have plenty of margin for error and one
could argue that you don't have to rest the decoction as
I've suggested since there are plenty of enzymes in the
main mash that will deal with the unconverted starches
if I simply brought the decoction straight to the boil, but I
figured that if I'm going to spend a long time mashing
and decocting the mash, an extra 20 or so minutes
letting the decoction rest at saccarification temps is not
a big deal in the greater scheme of things!

Sorry about the lengthy post and apologies for effectively
teaching the more learned brewers how to "suck eggs" but
it was something of an epiphany to me, and yet another
example of how this craft has never ceased to amaze me
since 1995!

Cheers,
Rowan
Canberra Brewers Club, Australia

[9588.6, 261.5] AR (statute miles)
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