Sorry to post to an older thread, but I wanted to comment on something I read here.
I think there is some confusion about how I was expressing pH values in my book. It definitely looks like some people are misinterpreting or at least misapplying what I thought I said.
I meant to say that I was expressing pH values at the temperature where they were active.
This was interpreted to mean that I was saying you should take pH readings of your mash at mash temperature.
You should only take pH readings at temperatures supported by your pH meter. Read the instructions that come with it. Many pH meters are designed to only operate on room temperature samples; using them at higher temperatures can damage the probes or shorten their useful lifespan.
What I wanted to say was that there is a relationship between temperature and pH, and that you had to account for the temperature. Some meters do this automatically, others don't.
I guess this came out of a conversation I had at Sierra Nevada (Jeff Rankert was there, maybe he remembers it). I was asking them about how they adjusted their brewing liquor and they said it was adjusted to pH 5.5. I asked if the quoted value of 5.5 was at room temperature or at mash temperature (where it would be used) since there would be a difference. They said it was at mash temperature. I think I followed-up because we were also looking at a pH meter that was measuring their mash pH; they said the same thing.
So that's what I meant, and where I got the information. I know pH is often expressed at room temperature (there's probably an ASBC standard for this that explains the details); I was trying to understand if the values were corrected for temperature or not.
The bottom line is that if I said the pH was a certain value at mash temperature, I was only saying to be sure it was a temperature-corrected value. Measure it at whatever temperature your meter supports, then adjust it if necessary.
I regret confusing an area that I was attempting to simplify.