Ask the Experts: Adding Lactic Acid | Craft Beer & Brewing

Ask the Experts: Adding Lactic Acid

Homebrew expert Brad Smith, author of the Beersmith homebrewing software and the voice behind the Beersmith podcast, answers a question on adding lactic acid to beer.

Brad Smith 1 year, 4 months ago

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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.

The reality is that this can be difficult to achieve. You can’t measure your mash pH until 5–10 minutes after you’ve mashed in, and an accurate pH reading is needed to calculate the lactic acid needed as an adjustment. However, you can predict the mash pH using software, although the prediction may not be perfect.

So the compromise I’ve reached is that I estimate my mash pH from the grain bill and water profile using software up front, and use that to estimate how much lactic acid I need to get myself into the 5.2–5.6 pH range. Then after I’ve had a chance to mash in and let the pH settle, I take a pH reading and verify that I’ve reached the target pH I was shooting for. If I’m off substantially at this point, I can make a second lactic-acid addition to reach the target level.

This compromise lets me hit my target range up front to cover cases where the mash conversion may complete quickly and then adjust it if needed after I’ve mashed in.

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