VikingChrisColby
Well-Known Member
A little basic chemistry tells us that the pH of an aqueous solution decreases with increasing temperatures. Some tiny percentage of H20 molecules split into H+ and OH- ions (or, in more modern descriptions, H3O+ and OH- ions) and the pH decreases. (So does the pOH, the negative log of the hydroxyl ion concentrations, so the overall acidity/alkalinity of the solution isn't changing even as the pH and pOH do. But I digress.)
The brewing literature is full of pH values, but do these refer to the actual pH (at mash temperatures), or the pH of a cooled sample? You'd think this would be a simple question, but you can find statements supporting both interpretations in the homebrew lit.
I had always thought -- and heard from professional, educated brewers that I trusted -- that these values were actual pH values. And this made a certain amount of sense -- if the values were for the solution at another temperature, wouldn't this temperature be mentioned? And, this also made sense given the pH values I was measuring in my (home) brewery.
Recently, however, I became convinced of the opposite, mostly based on second hand information, but second hand information from people I generally found knew what they were talking about. Today, however, I read this:
“The pH of the mash depends on mash temperature, and at 65 °C the pH of a mash is approximately 0.35 less than 18 °C because of dissociation of buffering substances. This difference must be considered when measuring pH and when declaring the ‘optimum pH’ for mashing events.
Although the precise picture will depend on the nature of the grist and the mashing regimes involved, it has been shown that the highest yield of extract and highest ferment ability occur at pH 5.3–5.8 (measured at 65 °C).”
--Charles W. Bamforth, "Scientific Principles of Brewing and Malting" (2006, American Society of Brewing Chemists)
At this point, I just want to know what to believe. I don't have access to the original scientific papers that established the pH optima we quote today. Does someone have access to a library that does and can see what the original authors did? (It should be in the materials and methods sections. A million thanks if someone could do this.)
Chris Colby
Editor
beerandwinejournal.com
The brewing literature is full of pH values, but do these refer to the actual pH (at mash temperatures), or the pH of a cooled sample? You'd think this would be a simple question, but you can find statements supporting both interpretations in the homebrew lit.
I had always thought -- and heard from professional, educated brewers that I trusted -- that these values were actual pH values. And this made a certain amount of sense -- if the values were for the solution at another temperature, wouldn't this temperature be mentioned? And, this also made sense given the pH values I was measuring in my (home) brewery.
Recently, however, I became convinced of the opposite, mostly based on second hand information, but second hand information from people I generally found knew what they were talking about. Today, however, I read this:
“The pH of the mash depends on mash temperature, and at 65 °C the pH of a mash is approximately 0.35 less than 18 °C because of dissociation of buffering substances. This difference must be considered when measuring pH and when declaring the ‘optimum pH’ for mashing events.
Although the precise picture will depend on the nature of the grist and the mashing regimes involved, it has been shown that the highest yield of extract and highest ferment ability occur at pH 5.3–5.8 (measured at 65 °C).”
--Charles W. Bamforth, "Scientific Principles of Brewing and Malting" (2006, American Society of Brewing Chemists)
At this point, I just want to know what to believe. I don't have access to the original scientific papers that established the pH optima we quote today. Does someone have access to a library that does and can see what the original authors did? (It should be in the materials and methods sections. A million thanks if someone could do this.)
Chris Colby
Editor
beerandwinejournal.com