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Contents:
  Re: Poorly fermentable wort (Fred L Johnson)


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Date: Tue, 5 Jul 2011 05:42:23 -0400
From: Fred L Johnson <FLJohnson52 at nc.rr.com>
Subject: Re: Poorly fermentable wort

Many thanks to all of you for the responses to my question on why my Belgian
wit wort was so unfermentable. Suggestions have included that the
saccharification temperature was too high due to uncalibrated thermometers,
dead space below a false bottom in the mash tun, uneven mash temperatures
through the mash, low beta amylase in the pilsner malt, and high gravity due
to dissolved proteins. 

Regarding the mash tun, there is no false bottom and the mash was stirred
well during frequent, gentle   heating. My thermometer is calibrated and
traceable to an NIST standard, so I trust the mash temperature values. The
mash had a negative iodine test for over thirty minutes before transferring
it to a lauter tun.

I suppose it is possible that there was insufficient beta amylase in the
grist, but that would not be characteristic of this malt. The published
Hartong Index for this malt is a range of 34-43%. Perhaps someone could
further comment on the possibility of low beta amylase activity, considering
50% of the grist was unmalted wheat. I suppose I could treat the beer with
amylase--assuming the enzyme will work under post-fermentation
conditions--and see just how much more fermentable this beer could be. I did
read from one professional brewer (Garrett Oliver of Brooklyn Brewing) that
he uses a "two-stage rest" with a "long" 152 degrees F saccharification rest,
but I don't know what "long" means to him and I don't know what the other,
undescribed rest is. Perhaps I need to really lengthen the mash time. 

The possibility of a high starting gravity due to soluble proteins seems to
me to be the most likely explanation for what I observed. One private email
suggested "...your protein rest is the culprit". I suspect this was referring
to my not actually having a proper protein rest. David Houseman also
recommended a more extensive mash profile including an acid rest, a protein
rest, a beta-glucan rest, and a saccharification rest. In this regard, I did
need to acidify the grist to get the pH down to 5.3 (at mash temp). But I had
no problems lautering this grist, for which a beta-glucan rest would be
indicated.

I suppose I could perform the old Lowry protein assay on the beer and
compare it to a beer that was more fermentable, but I'm not sure the Lowry
assay will react with short peptides that could be contributing to the
gravity. I know wheat beers contain more dissolved protein than an all-barley
malt beer, but I'm not sure how to easily determine how much of the gravity
is due to the protein or peptides without making up standard solutions of
beer proteins--too much trouble.

If the high final (and original) gravity is simply due to high protein
levels, do these types of beers need to have a more extensive protein rest? 
I don't see that high protein levels are actually causing a problem with the
beer. It seems that a high protein level merely needs to be accounted for
when formulating the recipe, determining an adjusted target starting gravity
to achieve the desired alcohol content of the beer.

Perhaps the simplest thing to do would to be to rebrew this with David
Houseman's suggested multiple rests just to see how much different the beer
could be with the extensive step-mash profile.

Any other suggestions?

Fred L Johnson

Apex, North Carolina, USA

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