The 0.35 difference is totally wrong. Kai Troester, Gordon Strong, and John Palmer all quote values of 0.18-0.25, which agrees with the experience of both you and I as well. 0.35 is way off.
And what remains important is that all references in the literature are to pH measured at ROOM temperature; whatever the displacement is, is therefore irrelevant; and, as you suggest, Dave, we can still debate the effects of pH on beer quality. We just need to have a standardized understanding of our reference conditions in order to do that.
Crazy. Some of these texts are quite old. Why on earth would they mention the differential and not specifically at what temp they measured mash pH?
“If more of us valued food and cheer and song above hoarded gold, it would be a merrier world.”
Short(ish) answer: When the concept of pH was first introduced and adopted by brewing scientists in the 1920s, the only methods for measurement relied on chemical reactions carried out at room temperature. Later, instruments (like we now use) were developed that use electroconductivity as a PROXY for pH. They can take a measurement at other temps. But mash ACTUALLY has a displacement. DeClerck reports a couple of tests demonstrating this, not to suggest that a correction factor might be available, but to emphasize the need to take readings at room temp. Since then it seems that only assorted homebrewers and Ashton Lewis on a bad day (the dude is a UC Davis grad) have had trouble with this.
From De Clerck:
The term: STP is widespread in chemistry. Standard temperature and pressure are important aspects since so many parameters can vary with those components. Its a stretch to assume that pH measurements were not conducted generally with respect to STP unless their deviation is specifically called out. Now, if there were only a true ‘standard’ to the STP. Unfortunately, even that isn’t fixed. But generally, somewhere around room-temp and sea level atmospheric pressure is typically used.
The pH offset between mashing temp and STP cannot be a fixed number unless a mashing temperature is applied. I’m assuming that most can recognize that the offset is zero at room temperature and it grows with increasing temperature. So the 0.18 to 0.35 offset range may have validity…but at differing temps.
I agree with every comment regarding STP. It is a scientific convention – whenever a scientist fails to mention temperature and pressure, it’s because conditions are at STP. If not at STP but the conditions are not specified, that would be very sloppy science indeed.
I’ve come totally full circle on this whole thing, arriving at more questions, including a key one: who cares!? View more continuing ramblings here:
Indeed, my beer tastes good! I do appreciate all the replies. This was definitely one of those WTH moments that I had to share and get a sanity check on.
“If more of us valued food and cheer and song above hoarded gold, it would be a merrier world.”
Don’t worry. Mr. wizard and I went rounds and rounds about our recent article. He would come back with edits that would literally blow my mind. I.e. oxygen solubility at boil is not zero.