Acidulated Malt is a pale malt (color: roughly 3 to 6 EBC/1.7 to 2.8 SRM) that has been subjected to a lactic acid fermentation after kilning and a second finishing drying cycle. The lactic-acid bacteria reside naturally in the malt. The purpose of acidulated malt is to reduce the pH value of the mash. Proper mash pH (5.4 to 5.6) helps assure the enzymatic performance on which the brewer relies to break down gums, proteins, and starches. It also leads to proper wort pH, which affects yeast performance during fermentation and the final flavor profile of the resulting beer. Every 1% of acidulated malt (by weight) of the total grain bill reduces the mash-pH by 0.1 point. In highly alkaline mashes, acidulated malt can make up as much as 10% of the grain bill.

The optimum wort pH of most barley-based beers is 5.2, and of most wheat-based beers is 5.0. Measurement of the pH values from the mash-in to the finished beer informs the brewer if a pH correction is necessary and how much acidulated malt, if any, should be used in the mash.

Acidulated malt is widely used in Germany, where the Beer Purity Law (Reinheitsgebot) proscribes the direct use of acids in the mash, the wort, or the finished beer. See reinheitsgebot.

See also malt and ph.