Tuesday, July 7, 2009

Measuring mash, wort, and beer pH

This past weekend I brewed up a quick batch of something that will be along the lines of an ordinary bitter or light blonde ale and decided to mess around with pH measurement. I took my mash samples and measured them with five instruments:

1) Economy pH test strips (universal range)
2) Economy pH test strips (mash pH range)
3) ColorpHast test strips
4) Hanna Checker meter
5) Martini pH meter with automatic temperature correction (ATC)

My early findings are as follows, and I promise to update this soon with some more solid data:

1) The ColorpHast strips are way off, as other users have found out.
2) ATC is pretty useful on a pH meter if you don't want to bother with either bringing your sample to a specific temperature, or measuring the temperature of the sample and calculating the correction.


Seanywonton said...

Whoah Tom, that's really interesting about ColorpHast strips being way off. I'd love to hear more. Especially if they are reading lower than the actual mash pH.

I just started using ColorpHast strips. I recently did a pale ale where the mash pH was surprisingly low: 4.7. I tried to get it higher with a little chalk, but I didn't want to add too much, so I never got the pH above 4.8. Everything about the beer turned out great. It's one of the best beers I've made IMHO.

Tom E said...

4.7-4.8 is really low, Sean. Your pH measurement on a strip will basically be at room temperature. The temperature on the strip will settle to room temperature really quickly - I think it's impossible to use a strip to get a pH reading at actual mash temp. The differential between room temperature pH and mash temp pH is approximately .35. So, if you were going for a mash pH of 5.2, you would look for a pH reading on the strip of 5.55.

So, if we can safely assume at this point that the colorpHast strips are off by .3-.4, we would say that your room temperature mash pH was measured at 5.1-5.2 (4.8 + .3-.4). Subtract the correction factor of .35 and your mash pH would have been about 4.75 to 4.85. That's pretty low.

Two thoughts on that...

1) Measuring pH with test strips is extremely prone to operator error. What looks like 4.8 to you could easily look like 5.2 to me. So Dr. Eagan recommends a vision check immediately.

2) In a lower wort pH, alpha acids are extracted less efficiently. Some people think that this lends a more pleasant bitterness, which may be something that's benefitting your pale ale.

Seanywonton said...

That's what I'm saying, the mash pH (measured at room temp) looked too low, but everything about the beer including flavor and mash efficiency would lead me to believe it was not low. So if you and others are saying these read about .3 lower than the correct mash pH, then actually I nailed it at 5.1.

I'll bring you a sample soon, see what you think. It might be interesting to do a post-fermentation pH reading too.

Tom E said...

But that's 5.1 at room temperature. The mash pH at room temperature will measure .35 higher than at actual mash temp, meaning your pH at mash temp was about 4.75.

That's one of the things that I find very confusing and misleading about pH measurements in brewing. For mash pH, the standards discussed in most of the literature you'll find (5.1 to 5.6 or thereabouts) are at mash temperature. Meaning that you actually want to measure a sample at 5.45 to 5.95 at room temperature. You can't hold a pH strip at mash temperature to get an accurate reading and most pH meters are not rated for mash temps.

However, when you read about pre and post boil wort pH (5.6-5.8 down to 5.2-5.4), those numbers are already assuming that you've cooled the sample to room temp. And as for beer pH (4.0-4.4) you have to de-gas the sample to get an accurate reading.

It's all a bit too confusing. In a little while I'm going to do a whole post about target pH's and how to measure. I've never been able to find it all in one place, so I figured I'd put it up here.

Seanywonton said...

Hey Tom,
I don't mean to contradict you (I am really just starting to understand this stuff myself), but the wort pH at room temp is going to be lower than the actual mash pH by a few points, not higher.

This is from Principles of Brewing Science page 49:
"The classic rule is for the chilled wort to have a pH of 5.0 to 5.2 and, to achieve this level, it is desirable to establish a mash pH in the range of 5.2 to 5.4."

So getting back to the example I gave, if my ColorpHast strips were indeed measuring up to .3 low, I might have hit my mash pH right on the head. This is really just a theory though, as I have never measured my pH strips against an electronic meter.

The bottom line is the beer tastes good, and I don't see any reason why (judging by the grains, water, and mineral additions used) my mash pH would be as low as 4.8.

Tom E said...

I looked back at the Fix book to understand the context of that quote that you posted, and I still can't make sense of it. All I can tell you is that it's incorrect.

I'd refer you to page 202 of New Brewing Lager Beer:

"Be aware that density and pH readings may vary with temperature, so the hotter the mash or wort sample is, the lower the density and pH appear to be."

and page 75 of Standards of Brewing, if you have that one:

"Remember that pH changes with temperature, and so wort at 149F will have a pH about .35 lower than that measured at 68F."

Also, have a look at note 2 on Palmer's nomograph (figure 81, bottom of the page here: http://www.howtobrew.com/section3/chapter15-3.html)

"The actual pH of the mash at mash temperature (150F) is typically .35 pH less than it measures at room temperature."

I can also tell you that my measurements with the meter with no ATC shows that the pH of the sample rises as it cools. This dude has been posting on the northernbrewer forum about pH quite a bit too and knows his stuff. His data shows the same:


Seanywonton said...

Yep. I see what you mean. Says so right here on the bottom of Palmer's nomogragh: the actual pH of the mash at 150 is .35 less than it measures at room tmeperature.

I'm going to go back and do some more studying up on this stuff. I still don't see how I could have ended up with such a low pH on such a pale beer with relatively low amounts of brewing salts added.

If you want to check out the recipe I was talking about it's here: http://seanywonton.blogspot.com/2009/06/meetification-pale-ale.html
The beer is tasty as hell and I can't taste anything that would lead me to believe that the mash pH was really low, so I'm guessing it may have been a reading error of some kind.