Mash pH and temperature?

[VikingChrisColby]

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

 

[VikingChrisColby]

One more quote I dug up on line today:

"Infusion mashes are best carried out at pH 5.2–5.4 (mash temperature), and so will give cooled worts with pH values of about 5.5–5.8."
--Briggs, et. al., Brewing Science and Practice" (2004, Woodhead Publishing)

 

[mabrungard]

My advice is to assess this for yourself. Try a standard recipe of yours that you know where you mashed at and then alter the water alkalinity for a subsequent version of that recipe to produce a differing mash pH. I and other brewers I trust have found that beers taste better when using this room-temperature mash pH guidance:

Malt focused styles: 5.2 to 5.4
Hoppy and bittered styles: around 5.4
Roastier styles: 5.4 to 5.6

Please don't forget that in the realm of commercial brewing for which Briggs and Bamforth are only concerned, efficiency is a significant concern. The minor flavor quality reduction can be overlooked to some degree. Another consideration is that the major driver of brewing research for the last 100 or so years has been the light lager. I don't consider the findings of either of these eminent brewing scholars particularly compelling when weighed against my own findings and those of others where beer taste is the PRIMARY criterion.

Another consideration is that the results of the mash pH goals I've suggested above will tend to produce a more fermentable wort than would be produced using the Briggs and Bamforth guidance. We homebrewers tend to utilize slightly higher mash temps to help offset that increase in fermentability and maintain the mouthfeel we desire in our beers. In a light lager brewing, long and low-temp mashes are typical. In addition, the relatively low SG means that they welcome more body in their wort from this pH adjustment.

There are plenty of ways to skin a cat. Thanks for illustrating that the light lager brewers produce a result that fits their needs.

PS: Don't forget that all pH measurements should always be performed at room-temperature if you prefer your expensive equipment to last.

 

[VikingChrisColby]

I understand that commercial brewers and homebrewers have different aims. My question was much more focused than that — I was simply asking if brewing researchers took the pH of hot wort or a cooled sample.
One of my undergraduate degrees is in chemistry and, because I took an instrumental chemistry course one semester, I have a fairly good idea of how a pH meter works. When I see pH measurements, I often wonder how they were taken. That's why I asked the question.

PS Congratulations on focusing on taste in your beers; they are probably much better than mine as my overriding goal is to maximize their refractive index


Chris Colby
Editor
beerandwinejournal.com

 

[zwiller]

Lots of conflicting info on the subject. Kinda wondering the same thing... Recently did an IPA at 5.6 to test going near the Briggs/Bamforth figures and it's a good beer. Really smooth. Hops are slightly courser than say 5.4. Reminiscent of an english beer but with the american C hop thing (used chico).

Slowly putting together a list of my own preferences and it is close to Martin's with the exception of lower for maltier. I think 5.2 is for the really crisp lagers and not so much for ales.

Bear in mind that the mash pH is not necessarily a kettle pH target. BMC could in theory mash at 5.7 and dose kettle with acid to lower to 5.2. Thus, providing max efficiency but adjusted with acid to taste. Bamforth would correct...

 

[ajdelange]

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.)

At 25°C pKw = 14 so [H+] = E-7 and the pH is 7.
At 30°C pKw = 13.8 so [H+] = 1.26E-7 and the pH is 6.9

so yes, heating pure water lowers it's pH. The M alkalinity shifts from 0.05315 at 25 to 0.05318 mEq/L i.e. it actually increases but not to any significant extent (30 nanoEq/L). It's P acidity increases too but only from .02106 to 0.02196. But this is for pure water and beer, wort etc are far from pure water (but not too far).

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.

Yes, you can and you even find disparities in the professional literature. Of the many books I've had my nose into over the years only 1 is clear and that is DeClerck. He explains that, at least at the time he was writing, pH assessment was done in the lab as there were no pocket pH pens available in that day and that by the time mash and wort samples were transferred to the lab they were cooled. He explicitly states that all pH measurements in his book are at lab temperature. And he says the best pH for mashing is 5.5 and the best kettle pH (at conclusion of boil) is 5.2.

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?

Good reasoning IMO. This is an argument I often advance.

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)

I measure slope of 0.0055 pH/°C. Applying this to Charlie's data would say highest yield at 5.3 to 5.8 + 0.242 = 5.54 to 6.24 at room temperature. Using the 0.0075 number published in DeClerck that would come down to 5.3 to 5.8 + 0.33 = 5.66 to 6.13. Do you believe, based on your own experience, that either of these represents the optimum pH range? Now Charlie is a brilliant guy and maybe he has literature to back up his assertion (usually when a statement like the one you have quoted is made in a paper or book there is a reference) but my experience tells me that better tasting beers are made at room temperature pH of 5.4 - 5.6. Now my optimality criterion isn't best fermentability or efficiency - it's the best tasting beer.

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.

Yes, actually you do. The JIB has put up tons of stuff at http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)2050-0416 and its all free (which I don't understand but I don't need to - only hope it stays free).

 

[VikingChrisColby]

Now Charlie is a brilliant guy and maybe he has literature to back up his assertion (usually when a statement like the one you have quoted is made in a paper or book there is a reference) but my experience tells me that better tasting beers are made at room temperature pH of 5.4 - 5.6. Now my optimality criterion isn't best fermentability or efficiency - it's the best tasting beer.

The statement I quoted is in a text of his, and unfortunately he doesn't give a citation.
I've found that when I make brewing liquor that seems reasonable (sufficient calcium, some attempt to match alkalinity to beer color), my pH (from cooled samples) is usually around 5.6. I haven't done side-by-side tests at other pH values for extract efficiency or wort fermentability, but things always seem to go well when the pH is right around 5.6 (cooled). Lautering is never a problem, the hot break usually looks nice, and the wort and resulting beer taste good. (Anecdotally, for dark ales, I've found that a mash pH of 5.7 (cooled sample) seems to result in more malt aroma and better character in the roast flavor and aroma. I haven't done a side-by-side to confirm this, however. This is just an observation from a couple of batches, a porter and a stout.)


Chris Colby
Editor
beerandwinejournal.com

 

[VikingChrisColby]

Yes, actually you do. The JIB has put up tons of stuff at http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)2050-0416 and its all free (which I don't understand but I don't need to - only hope it stays free).

Woo hoo! Wow, that is great.


Chris

 

[zwiller]

Good info. THANKS

I should mention that the IPA I did @ 5.6 was fairly pale and I was surprised how much color it picked up compared to 5.4 with same grain bill.

 

[pjj2ba]

Welcome to the world of scientific literature. Even when reading peer reviewed articles in my field, the materials and methods sections are often woefully lacking in details like this. At least with enzymology studies, the values given are expected to be at STP (standard temperature and pressure) unless otherwise noted. Unfortunately, they are not always otherwise noted very well.

My assumption would be room temperature pH measurements - at least from the actual scientific articles. Someone's blog - who knows.

I agree with you, and with Martin. Yes, it is confusing (maddeningly so - what is the point of reporting it, if you don't give enough details so folks don't have to find out for themselves?). This then suggests that perhaps it is something that should be tested and then documented and shared. I might be able to do some testing.