A Craft Beer & Brewing Magazine reader recently asked us the following question:
I’ve bought lactic acid to adjust my mash pH, but when is the best time to measure my pH and then add the lactic acid?
Mash pH is most critical during the main conversion step, when the complex sugars in the crushed grains are being converted to simpler sugar chains that yeast can consume. This occurs in the temperature range of roughly 148–156°F (64–69°C), which is where most brewers mash in when doing a single-infusion mash. This is the phase when you need to get the pH right.
Today, we use highly modified malts that have a lot of enzymes to facilitate this sugar conversion, which means the conversion can happen very rapidly. In some cases, the mash conversion can be complete in as little as 20 minutes. So in an ideal world, you would add your lactic acid before you mash in so you can precisely hit your target mash pH (typically the 5.2–5.6 range) up front.