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	FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
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Contents:
  pH and temperature ("A.J deLange")
  Brix and Plato ("A.J deLange")
  Re: Mash Temp and Color (Kai Troester)
  acid bath for wort chiller? (Jon Fischer)


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Date: Tue, 30 Sep 2008 08:55:45 -0400
From: "A.J deLange" <ajdel at cox.net>
Subject: pH and temperature

RE: "... no practical ways (for the home brewer) to measure the mash pH 
ant mash temp. Both strips and meters are designed to measure pH of a 
cooled sample. And the ATC feature of a pH meter doesn't compensate for 
the pH shift of the mash."

The second part of the statement is true enough - ATC does not account 
for pH shift (which is caused by the temperature dependence of the pK's, 
which are measures of the energy required to remove protons from  the 
acids in the mash). It merely accounts for the the fact that the 
response of the electrode is E0  +  (R*T/F)*log[H+] with E0, R and F 
being constants, T the temperature and [H+]  the hydrogen ion activity 
(concentration) which does in fact change with temperature through the 
pK's as mentioned above. Apologies to Chad for logs 2 days in a row. It 
is very important that people understand that there are two distinct 
mechanisms: a) the shift in actual pH with temperature and b) the change 
in the response of a pH electrode with temperature to whatever pH is 
encountered.

Now the first part of the statement is not quite true. Today's meters 
are generally capable of measurement at mash and even kettle 
temperatures. The instructions that came with your meter or electrode 
should specify the range of temperatures that it can handle.

Referring to the points above if you dunk your electrode into the mash 
tun or kettle you will read the pH at the temperature of the mash or 
wort provided that your meter is ATC equipped as nearly all are these 
days. If you remove a sample from the same mash or wort and cool it to 
room temperature you will note a rise of a couple of tenths of a point 
as the mash or wort cools. Despite the opinion of giants in the industry 
such as Jean DeClerck that "..the pH should be measured at the 
temperature of the reaction." [Vol. I p267] it is usual to measure at 
laboratory temperature and the ASBC Method for pH determination of worts 
prescribes this. The clear advantage of doing so is that variation in 
measured pH over the course of a mash/boil cycle are those caused by the 
chemistry of the mash and are not masked by the fact that, for example, 
a protein rest was done at 124 F and a saccarification rest at 149. A 
not so obvious advantage is that the working part of most electrodes is 
still a very delicate, very thin glass bulb which is subject to 
considerable thermal stress as it is thrust into boiling wort or hot 
mash and again when it is remove to cool air. This was posted here years 
ago by someone who was involved in the manufacture of these things, as I 
recall. I can personally testify that since I have started taking all 
measurements at room temperature my electrodes last much longer and at 
the prices they command that is definitely a good thing.

A.J.


Return to table of contents


Date: Tue, 30 Sep 2008 09:16:34 -0400
From: "A.J deLange" <ajdel at cox.net>
Subject: Brix and Plato

The work of the Normaleichungskomission under Dr. Plato was undertaken 
in order to correct the Brix tables to Teutonic levels of precision.  
The Brix tables in turn represent an improvement on the original work of 
Balling. In all three cases the object was to obtain values of specific 
gravities for solutions of sucrose of given strength by weight (i.e. 10 
P or 10 Brix represents 10 grams of sucrose in 100 grams of solution). 
The reference temperatures for the specific gravities were different but 
when reduced to the same reference temperature the differences between 
the Brix specific gravities and Plato specific gravities are in the 5th 
and 6th decimal places. At the level at which refractometers and 
hydrometers work, Brix and Plato are, thus, the same.

A.J.


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Date: Tue, 30 Sep 2008 10:39:17 -0400
From: Kai Troester <kai at braukaiser.com>
Subject: Re: Mash Temp and Color

Kevin,

> I made two experimental 3 liter batches of about 10 deg P OE this
> weekend.  Both were
> 100 percent Maris Otter.  I mashed one at 65 deg C (149 deg F) and the
> second at
> 70 deg C (158 deg F).  All other variables, as best I could control,
> were kept the same.
> (OEs were 10.4 and 10.6 deg P). Interestingly the wort from the low temp
> mash was
> noticeably darker than the high temp mash.  I was not expecting the
> difference, but
> should I have?  They are in 1 gallon jugs so the difference is unmistakable.

How much darker are we talking about here? Did you measure the wort  
pH? I expect it to be about the same as I expect that you used the  
same water for both batches.

One cause that I can think of is that the lower temperature mash  
created more simple sugar and amino acids than the higher temperature.  
These are the the compounds that react to during maillard reactions.

In addition to that, maybe the pH of the higher temp mash dropped  
further due to the increased reaction between calcium/magnesium and  
malt phosphates. Decoction mashes are known to lower the pH further as  
a result the increased precipitation of phosphates.

Kai




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Date: Wed, 1 Oct 2008 11:21:47 -0700 (PDT)
From: Jon Fischer <fischjon at yahoo.com>
Subject: acid bath for wort chiller?

Hello Friends,
I have been using a flat plate counter flow wort chiller with great
success until I recently noticed a drop in performance. I am trying 
to clean it, based on the manufacturer's advice which includes a soak 
in 5% food grade acid such as citric or phosphoric. 

Would any of you recommend that I use a 5% solution of "Star San"? 
If so, how should I make a 5% solution.
Thanks,
Jon Fischer
Columbus, Indiana




      


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