When and How to Measure and Adjust Mash pH for Beer Brewing

At a recent homebrew club meeting, one of the members asked me a brilliant question – when and how should you adjust your mash pH when all grain beer brewing? This is a devilishly complex question as you want to adjust your mash pH quickly if brewing with modern malts.

The Mash pH Conundrum

I and others have written extensively on the importance of controlling your mash pH and maintaining it in the range of 5.2-5.6 during the sugar conversion step. A proper mash pH contributes to better flavor, complete conversion, and improved long term stability.

You can use additives like lactic acid and phosphoric acid to quickly adjust your mash pH, and I wrote an article recently on the purchase and care of a pH meter. So one might assume you can just use your pH meter to measure the mash pH after dough-in of the grains and then adjust it using lactic acid from the homebrew shop — right?

The problem is that most modern malts are very highly modified, which means they have a lot more enzymes (diastatic power) than is really needed to convert the sugars in your crushed grains into fermentable forms. Time is also working against us since it takes easily 10-15 minutes to dough in and stabilize the mash pH so it can be measured. Modern highly modified pale malts can in many cases convert the sugars within 20-30 minutes.

It could take 10-15 minutes to dough in, and another 5-10 minutes to get the mash sample down to room temperature to take a proper measurement then calculate and add the right amount of lactic acid. Which means it is possible for the majority of your conversion step to be complete before you’ve measured and adjusted your pH!

Managing Mash pH Properly

Fortunately you can estimate both your predicted mash pH and the predicted acid adjustment needed using software. Here’s a detailed article on how to do it in BeerSmith. The only problem here is that the pH estimate is exactly that – an estimate!

So the compromise I’ve settled on is to use BeerSmith to estimate my mash pH, then use that estimated value to determine the amount of lactic acid to use. Then what I do is add about 80% of that acid up front before I mash in. This usually gets my mash pH within the acceptable 5.2-5.6 range, and then I will take a measurement with my pH meter after I dough in and make any fine adjustments needed with some additional acid based on that measurement.

The advantage of this technique is that by adding most of the acid up front, I’m assuring that the mash pH starts in the acceptable range. However, by also measuring and making a final pH adjustment I’m assuring that the pH is stable if the mash conversion takes longer but most importantly assuring the correct pH to support the long term stability of the beer.

This is the best compromise between treating your mash based only on an estimate, and treating your mash pH based on an actual pH measurement.

I hope you enjoyed this article on mash pH. If you have any additional thoughts on adjusting your mash pH please leave a comment below. Thanks for joining me on the BeerSmith Home Brewing Blog. Be sure to sign up for my newsletter or my podcast (also on itunes…and youtube…and streaming radio station) for more great tips on homebrewing. Also check out the How to Brew Video series I shot with John Palmer if you want to learn more about all grain brewing.

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