HOMEBREW Digest #5632 Mon 30 November 2009

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  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 - ---------------------------------------------------- If you have received this transmission in error please notify us immediately by return e-mail and delete all copies. If this e-mail or any attachments have been sent to you in error, that error does not constitute waiver of any confidentiality, privilege or copyright in respect of information in the e-mail or attachments. Return to table of contents
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) - ---------------------------------------------------- If you have received this transmission in error please notify us immediately by return e-mail and delete all copies. If this e-mail or any attachments have been sent to you in error, that error does not constitute waiver of any confidentiality, privilege or copyright in respect of information in the e-mail or attachments. Return to table of contents
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