There are some answers that I write where I know that I am stepping into a gray area, and my very brief sidebar about pH jumped square in the middle of the gray area. To recap what is being addressed with the questions above (just a sample of the many received at BYO), I wrote the following in a “Mr. Wizard” column in the October 2017 issue:
The rule-of-thumb pH range of 5.2-5.5 is the pH of the actual hot mash, not the cooled sample. This means that the temperature-corrected pH is about 0.35 units higher, or pH 5.55-5.85. It is really best to use pH meters without automatic temperature compensation (ATC) because the ATC only accounts for the difference in how the electrode output voltage is affected by temperature and if you use the output from a temperature-corrected pH the result is confusing to compare to data published in the brewing literature.
Those 88 words generated quite the stir and we received several emails all questioning the validity of what I wrote. The questions from Dan Pixley, Jonathan Huron, and Lucas Frank represent the questions from other readers, so we have printed these three selections to preface this response.
I have spent many hours reading, thinking, and discussing this topic before sitting down to address the topic of mash pH. The one thing that I am certain about with respect to this topic is that it is pretty deep. In an effort to keep organized I am structuring my response into several sections. Hopefully this answer is clear and sheds light on the topic.
APPETIZER OF CROW
I have never been a huge fan of having to eat crow and I do my best to research my answers in an effort to avoid this unpleasant dish. But now is the time to eat a little crow about automatic temperature compensation (ATC). Plain and simple, I bombed the part about ATC. Contrary to the blanket statement in my reply, it is best to use pH meters with the ATC function.
A bit about pH before taking a shallow dive into ATC. pH is defined as the negative log of hydrogen ion concentration, and it turns small concentrations into larger values. For example, if the concentration of hydrogen ions is 10-5 molar (0.00001 moles of hydrogen ions/liter of solution), the solution pH is 5. The pH of any solution changes with temperature because the dissociation constant of a weak acid-base pair, the pKa, is temperature dependent. This means any solution containing weak acid-base pairs will exhibit a pH change when temperature is varied. Since pure water is a weak acid-base pair (H20 H+ + OH–), the pH of any aqueous solution, including strong acids and bases, is temperature dependent. ATC is not used to report measured pH to a standard temperature. This was my mistaken understanding about ATC.
The reason that ATC is important when measuring pH is that the pH electrode response to pH varies with temperature. This is generally considered a temperature error, and the magnitude of the error is very close to 0.003 pH units/˚C/pH variance away from pH 7. This error is a function of the pH probe, and not the solution being measured. Tables can be used to make this correction, but most pH meters come equipped with ATC and this task goes away. pH meters with an ATC functionality are convenient to use and allow pH for measurements over a wide range of temperature.
THE MAIN COURSE
The crux of this topic is what is meant by the various, and widely varying, pH ranges for mashing found in the brewing literature. My view is that references in the literature refer to mash pH, measured at mash temperature. Not mash samples that have been cooled to room temperature and measured. Why is this my belief?
Malting & Brewing Science:
A primary reference on this subject is the textbook Malting and Brewing Science (Briggs, Hough, Stevens, and Young), and in this text there is an oddly worded paragraph that contains the following:
The pH of mash or wort alters with
the temperature. At 65˚C (149˚F)
the pH of mash will be about 0.35
unit less than at 18˚C (65˚F), owing
to the greater dissociation of the
acidic buffer substances present.
Therefore, enzymes whose pH optima
are known from determination at 20˚C (68˚F) appear to have higher pH optima in the mash if this is cooled, as is usual, before pH determination. An infusion mash is best carried at pH 5.2-5.4. Consequently, the pH in the cooled wort [from this mash] will be 5.5-5.8.
To paraphrase this confusing paragraph, if one determines the pH of mash at 65 ˚C (149 °F), for example, to be pH 5.35, the mash will be pH 5.70 (5.45 + 0.35) at 20 ˚C (68 °F). The sentence about pH measurements being made at room temperature is clear, but then he goes on to state that the optimal pH range for infusion mashes is pH 5.2-5.4, and converts this range to wort pH. I have never been clear about the distinction between mash and wort in that paragraph.
The effect of water hardness on wort pH after decoction mashing is illustrated in Table 1 on page 22 — this table is based on one found in Malting & Brewing Science (Hopkins and Krause, Biochemistry Applied to Malting and Brewing, 1947). I have applied the 0.35 offset to show pH at mash tun temperature of ~65 ˚C (149 °F) as a point of discussion.
These data show how water chemistry influences mash pH. But the table also exemplifies how it is easy to be confused by pH ranges if temperature is not considered.
So that is my reference for the pH 0.35 offset between mash temperatures and room temperature. Not the clearest reference, for sure, but internally consistent. Incidentally, the Hopkins and Krause reference from 1947 is the only textbook reference I can find that unequivocally provides a temperature reference associated with pH data.
Dr. Charlie Bamforth states in “pH in Brewing: An Overview” (MBAA Technical Quarterly, Volume 38, Number 1, 2001, Pages 1-9): “There have been surprisingly few (if any) detailed studies of the precise impact of pH on mashing performance and wort composition. Textbooks of brewing make reference to “optimum” pH’s for parameters such as extract and “wort filtration”, though they are conspicuous by the lack of references. One textbook refers to a previous textbook! It seems that a largely empirical approach has been employed. How the data has been generated and on what scale (lab mashes are not always good mimics of commercial mashes) is unclear.”
John Palmer was cited in two of the emails that we received at BYO, so I dropped John an email and followed up with a phone call to make sure I was understanding his views. John sent me a presentation he gives about brewing water, “Putting Brewing Water in Perspective”, as a reference.
In this presentation, Palmer cites mash pH ranges in the literature referenced to mash temperature (Bamforth and Briggs), and also cites a pH range in the literature referenced to room temperature (Kunze). He uses a temperature offset of pH 0.25 (more on that later), as opposed to the 0.35 offset from Malting and Brewing Science. Here is a summary of what Palmer reports for the best pH range for optimal extract yield, by source (the range from my answer in question is included in for comparison), and with Palmer’s 0.25 offset included:
Bamforth’s range is: 5.3 to 5.8 (mashtemp) / 5.55 to 6.05 (room temp)
Briggs’ range is: 5.2 to 5.4 (mash temp) / 5.45 to 5.65 (room temp)
Kunze’s range is: 5.25 to 5.35 (mash temp) / 5.5 to 5.6 (room temp)
Lewis’ statement: 5.2 to 5.5 (mash temp) / 5.45 to 5.75 (room temp)
The Kunze temperature reference is anecdotal because his textbook does not reference temperature, and Palmer bases his temperature reference on a conversation he had with Dr. Ludwig Narziss (Weihenstephan Center of Life and Food Science’s former head of brewing science for over 40 years).
When I look at these data, I see two things. The first is that there seems to be a “lost in translation” effect in play, where one camp is arguing a moot point against the opposing camp because of the difference in reference temperature. The second thing is that these ranges are all pretty similar.
Palmer discusses mash pH and beer flavor in his presentation, and distinguishes between optimal pH ranges for extract yield/enzymatic activity and optimal pH ranges for beer flavor. As it turns out the two brewing objectives are not always satisfied by the same mash pH. Go figure! That is another discussion for another day. And to very briefly touch on why Palmer uses a pH offset of 0.25, instead of 0.35. This offset is a function of the buffer systems that are present in malt and is empirically determined.
Anyone remember the outdated declaration that Canadian beer is stronger than American beer? Go to Canada and buy that strong beer at 5% alcohol, as opposed to the weak stuff down in the U.S., weighing in at a meager 4% alcohol. Well, in case your gray hairs are still developing, that argument was quite prevalent “back in the day”. Back in the day, most U.S. brewers expressed alcohol by weight (ABW), and Canadian brewers used alcohol by volume (ABV). 5% ABV = 4% ABW. That is what I call lost in translation.
This topic has quite literally plagued me for 25 years because the textbook references are simply not clear, and they don’t adequately discuss the influence that temperature has on mash pH. So I went digging for other data that may help shed light on this topic.
Data set #1 came from Rahr Malting Company, my employer and a family-owned and operated company since 1847. Malting companies analyze each lot of malt so that brewers know what they are buying. One of the analyses performed is for extract potential. This test uses what is known as a Congress mash to produce wort from a malt sample. 50 grams of malt and 400 ml of distilled water are always used in the Congress mash method, along with a standard mashing profile, to produce wort. The primary use of this wort is to determine the hot water extract (lab yield) of the malt sample. pH of the wort is also measured and reported. The average wort pH (measured at 20˚C/68 °F) from 100 samples taken from 100 different batches of malt from production lots of North-American, pale, 2-row malted barley was pH 5.98 (data not published and taken from internal lab results from 2017).
As a point of reference, Congress wort is produced using an ASBC (American Society of Brewing Chemists) method, and that method specifies distilled water. As illustrated by Hopkins and Krause (1947), some brewing waters lower pH (those weighted towards calcium and magnesium), and other brewing waters increase mash pH (those weighted toward carbonate). So Congress wort pH values are almost always different from actual mash pH values made using brewing water (i.e., not distilled water).
So let’s focus on the average pH 5.98 from the Rahr data set from Congress wort samples. This is at 20 °C/68 °F, so it translates to between pH 5.63 to 5.73 depending on the pH offset (pH 0.35 to pH 0.25 as discussed earlier). This is real data, and puts the wort pH from these 100 samples right in the mix of the room temperature values from the previously cited sources (Bamforth, Briggs, and Kunze). It is also consistent with Hopkins and Krause (pH 5.76, room temperature, distilled water).
I ran a benchtop trial to play with temperature and mash thickness because I wanted a sanity check on my conclusions. I made a mash with Weyermann Pilsner malt and distilled water at a mash thickness that is typical for infusion mashing and then thinned out to ASBC Congress mash specifications. pH was measured using an EcoTest pH 2 meter (ATC type pH meter), and the meter was calibrated using pH 7.0 and pH 4.0 buffers. What I measured is found in Table 2 on page 22.
This is really a crazy topic. If temperatures were referenced in the literature this would be a non-topic. The more I think about this topic, I truly wonder if some of the references in the literature were intentionally vague. So many things about brewing require the brewer to hone their individual process because there are simply too many variables to consider to make rules of thumb terribly useful. I specifically avoided addressing the question of “what is the right pH range” because there is no definitive reference. I think that topic would require a full feature story and not one I am ready to take on in a “Mr. Wizard” column.
I am a practical brewer and think in terms of how things really happen in practice. If a brewer wants to know mash pH after mash-in is complete, the quickest way to take the sample is by plunging a pH probe into a sample grabbed from the mash. The pH is noted, and off to the next task. If this is how you brew, great. Just remember that your mash pH 5.4 at 65 °C (149 °F) may be another brewer’s mash pH 5.7 at 20 °C (68 °F).
I am confident in this reply and am sticking to it!