Wednesday, July 29, 2009

On pH Measurement

On my most recent brew day, I took pH measurements throughout and took some pics. Not sure how much use the pictures of the strips will be - they don't always jive with what they looked like to my naked eye as I read them. I'll describe each step where I took measurements, what they mean, and how you as a homebrewer should look to take measurements as you go.

Mash pH

Much has been made about mash pH, and I won't get into it all over again. I think that John Palmer's How To Brew gives as fine a rundown on mash pH as anything out there and it's already up on the web. If you want to understand how residual alkalinity works, how different minerals affect mash pH, and how to dial your mash pH into the correct range, read up. I'll wait...

I think that the most frustrating thing about the discussion of mash pH is that nobody tells you how to measure it. I'll attempt to address that in this very space.

You'll often hear that your mash pH should be 5.2. It's a common statement that you'll hear from brewers. And there's truth to it. Palmer says that mash pH should be in the 5.2-5.6 range and this is for a number of reasons; optimal enzymatic activity in the mash, wort and beer clarity, healthy fermentation, a more pleasant hop bitterness, finished beer flavor, and more.

However, when it comes to measuring mash pH, there's a critical point that should not be overlooked. Palmer makes it himself, but for the best and most succinct explanation, I'll refer to page 75 of Dr. Charles Bamforth's Standards of Brewing:

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

With that in mind, let's think about a couple of things:

  1. Most pH meters that we homebrewers can afford are not rated to take measurements at standard mash temps (145 to 158F).

  2. When you take a measurement of your hot mash pH with a pH strip, it almost immediately comes to room temperature once you're looking at it out in the air, up against the guide on the package, or against a white background of your choosing. You don't read the strip while it's immersed in the hot mash.

So, even though your mash at mash temperature should be 5.2 to 5.6, you're actually going to look to read 5.55 to 5.95 at room temperature (68F). In the case of my most recent brew day, I took a 3 oz sample from my mash and cooled it to room temperature. I took pH measurements with five separate instruments and here are the results with some pictures:


Economy wide range strip reading: 6.0 (+/- 1.0 pH)













Economy 4.6-6.2 range strip reading: 5.8 (+/- 0.2 pH)













ColorpHast pH strip reading: 5.8 (+/- 0.3 pH)













Hanna Checker meter: 6.06 (+/- 0.1 pH)




Martini meter with ATC: 6.04 (+/- 0.1 pH)








The first thing that I learned from these readings was that my mash pH was higher than what I wanted. I made an addition of a 10% phosphoric acid solution to my mash to lower the pH and came up with the following readings:

Economy wide range strip reading: 6.0 (+/- 1.0 pH)













Economy 4.6-6.2 range strip reading: 5.5 (+/- 0.2 pH)













ColorpHast pH strip reading: 5.3 (+/- 0.3 pH)













Hanna Checker meter: 5.55 (+/- 0.1 pH)




Martini meter with ATC: 5.52 (+/- 0.1 pH)








This brought me to a mash pH of about 5.2 (correcting the Martini meter from 5.53 - 0.35 = 5.18). What I learned from these two sets of data was the following:

  1. The meters are simply much more accurate than the strips, both in their stated levels of accuracy and in the elimination of operator error. Which leads me to...

  2. The strips can be difficult to read. The difference between 5.5 and 5.8 on the economy (4.6-6.2) strips and 5.3 and 5.5 on the ColorpHast strips is extremely subtle. I honestly don't know that my eyes can tell the difference between 5.3 and 5.5 on the ColorpHast strip.

  3. The ColorpHast strips seem to measure consistently low. There's a fella who's been doing a study of the shift on the ColorpHast strips and he's determined that they're pretty consistently off by about -0.3 from actual pH.

  4. Having ATC (automatic temperature correction) on the meter is pretty useful. In the case of this exercise I took a lot of time out of my brew day to take measurements and pictures. But on a normal brew day I absolutely would not want to. With ATC I only really need to get my sample into a reasonable temperature range to get an accurate reading. I don't need to get the sample to a specific temperature, which makes it easier to get an accurate reading on the fly.
Pre-Boil Wort pH
Mash pH is the most critical measurement. In theory, if you get your mash pH dialed in, your wort pH both pre and post boil should follow correctly. However, measuring wort pH both pre and post boil can be a valuable tool in troubleshooting, as was the case in my most recent brew day.

I brewed a light lager this time around, which meant a really light beer that would push my pH towards the upper limits - no roasted malts to acidify the mash. It also meant a really low original gravity, and the possibility of a weaker, more alkaline sparge. I didn't fly sparge the mash this time around - I batch sparged. So I didn't get to test the pH of the runnings throughout the sparge. That might have been illuminating. Maybe next time. Anyway, here are the results of the pH measurements of the pre-boil wort:

Economy wide range strip reading: 6.0 (+/- 1.0 pH)










Economy 4.6-6.2 range strip reading: 5.8 (+/- 0.2 pH)










ColorpHast pH strip reading: 5.5 (+/- 0.3 pH)











Hanna Checker meter: 5.73 (+/- 0.1 pH)





Martini meter with ATC: 5.76 (+/- 0.1 pH)


As per this BYO article by Steve Parkes, wort pH should drop from the 5.6-5.8 range pre-boil, to the 5.2-5.4 range post-boil. My pre-boil pH seemed to be fine. The rise in pH from mash during the sparge would be explained by basically dilluting a high gravity, highly buffered wort, with water at a higher pH. In this case I seemed to be fine. However, after a 75 minute boil...

Post-Boil Wort pH

According to the same Parkes article, the drop in pH during the boil;

is primarily due to the precipitation of calcium phosphate. Calcium ions in brewing water reacts with phosphates from the malt to form calcium phospate and hydrogen ions, which lower wort pH.
However, my post-boil wort pH measurements were:

Economy wide range strip reading: 6.0 (+/- 1.0 pH)









Economy 4.6-6.2 range strip reading: 5.8 (+/- 0.2 pH)









ColorpHast pH strip reading: 5.5 (+/- 0.3 pH)









Hanna Checker meter: 5.76 (+/- 0.1 pH)




Martini meter with ATC: 5.80 (+/- 0.1 pH)



If anything, my wort pH went up (if only slightly)!!! I wonder why? Steve...

This demonstrates the importance of excess calcium ions in the wort after mashing. For this reason, it is sometimes a good idea to add gypsum to the kettle. If your mash pH is fine, but the pH does not drop to at least 5.4 by the end of the boil, add 1/4–1/2 teaspoon of gypsum per five gallons.

And in my case, I have extremely soft water that is very low in calcium. And my wort did not drop to 5.4 by the end of the boil. What would be the impact of that? For one, higher wort pH during the boil is associated with a harsher bitterness extracted from hops. Additionally, higher wort pH usually means higher beer pH, which in turn means a "flatter" tasting beer and a beer that is slightly more susceptible to spoilage by bacteria.

So, I would reckon that this exercise was valuable from a troubleshooting perspective. I was able to monitor my mash pH and dial it in to the right range. I was also able to determine that I may not have enough calcium in my mash and wort to drop the pH during the boil.

Let me know what you think.

7 comments:

Seanywonton said...

Thanks for doing all that testing so I don't have to! Good to know! Brew Strong.

Wurst/Whorst- Brewing Arts Instructor, CEO APRK said...

What is the alkalinity of your water expressed as CaCO3? Mine's about 110 and I use anywhere between .5 cc's to 1.2cc's of 88% strength lactic acid to the mash. Gypsum and Calcium Chloride additions will also help lower your alkalinity, but not significantly.

Tom E said...

The alkalinity of my water as CaCO3 is about 40. I've used gypsum, calcium chloride, and phosphoric acid (and various combinations thereof) with success to lower my mash and wort pH.

Wurst/Whorst- Brewing Arts Instructor, CEO APRK said...

40 ppm of CaCO3 is nearly perfect for brewing a range of beers ranging in color from light to fairly dark(red). You don't need phosphoric acid. Depending on what you're brewing, I wouldn't add anything but gypsum and calcium chloride to bring up your calcium and sulphate levels respectively. TTBC.

Tom E said...

My water is perfect for brewing most beers from the dark gold/light amber/copper range to brown. I rarely need to touch anything if I'm in that range. When I brew really dark beers I need to raise pH and when I brew really light beers I need to lower it. Please keep in mind that I'm not basing those comments on theoretical estimates from spreadsheets and charts. I'm basing this on actual measurements taken during the brew day.

So if I'm brewing a really light, delicately flavored beer, and I don't want a lot of flavor contributions from sulfates or chlorides, I find the use of a food grade acid necessary to lower pH.

Thanks for your comments.

thatguy314 said...

Tom,

Have you tried calibrating your pH meter by raising the temperature of your standards? Most standards show their pH variance based on temperature at the bottle. If the pH meter doesn't automatically adjust for temperature, you may just try to calibrate your meter for the temperature you plan to use it at (~150ish i imagine).

Tom E said...

I'm not aware of any economy or handheld pH meters that are rated for standard mash temps (i.e. 150F). I know that the Hanna Checker and the ph56 are rated for a maximum of 120 and 140 respectively.

I think it's good practice to make all measurements at the same temperature, and since most of the literature that's out there quotes 68F or "room temperature", that's what I go for.