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Old 10-03-2012, 06:13 PM   #11
ajdelange
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Quote:
Originally Posted by Kaiser View Post
A.J. has a point in that the malt’s buffer capacity is also affected by the pH of the mash.
I wasn't particularly trying to make that point. Buffer capacity and pH are intimately related but it also depends on how much of which buffers are present. Malt contains I'd guess dozens of acid/base pairs with phosphoric/mononbasic phosphate and monobasic phosphate/dibasic phosphate most likely the predominant ones but as at mash pH one is about halfway between the pK's of those two their buffering is minimal so it may well be some other pair or the combined effect of several pairs that are responsible for observed DI pH.


Quote:
Originally Posted by Kaiser View Post
There was an interesting and fairly strong correlation between base malt DI pH and its buffer capacity. The higher the DI pH, the lower its buffer capacity.
That's interesting because it implies that one is moving away from a pK at higher DI mash pH when one is in fact moving closer to the 7.2 pK of the phosphate system thus implying that it is other systems that are mostly responsible.[/QUOTE]


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Originally Posted by Kaiser View Post
The change in buffer capacity was not large enough that I think it needs to be considered in the mash pH estimation, though.
In my limited experiments I found values from 14 - 35 mEq/kg-pH but as noted earlier don't place a lot of confidence in those measurements. Also I noted that some malts had buffering linear over pH and some didn't but I'm not sure the observed non linearity was real i.e. it might have been drift in pH caused by slow reaction times.
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