When most homebrewers consider pH in brewing, they think about achieving the proper mash pH. However, hitting the proper boil pH (of 5.1–5.2) is also important. Having wort in the right pH range at the end of the boil has a few benefits, most notably better hot break production. As wort pH decreases, there is also less color pickup in the boil and hop bitterness becomes more pleasing, although hop utilization decreases.
Sometimes (perhaps most times), having an ideal mash pH of 5.2–5.6 will ensure that your boil pH drops into the proper range without any intervention by the brewer. However, this is not guaranteed. Two different unboiled worts can start at the same pH, but end up at different post-boil pH levels, even if they are boiled for the same time and at the same intensity. Most often, if the boil pH is out of range, it is too high.
Fortunately, there is an easy way to check on your boil pH and adjust it — all without requiring a pH meter or anything you don’t likely already have in your brewery.
Below a pH of 5, the coagulation of proteins decreases. (Hot break, the light-colored flakes that form in your kettle during the boil, is coagulated protein.) Above a pH of 5, the amount of protein coagulated is constant, but the break material looks different at different pH levels. At a pH of 5.2, hot break is seen as relatively large, fluffy flakes floating in otherwise clear wort. In some cases, these flakes may even clump together into larger “globs” of break material. The farther you move away from a pH of 5.2 (in either direction), the smaller hot break particles become. A few tenths of pH point away and the wort may simply look cloudy. So, you can use the presence or absence of big, fluffy hot break flakes as an indication of whether or not you are in the right boil pH range. The malts you use also effect the appearance of the hot break. Their protein levels and amount of protein modification achieved in malting also play a role.
The same chemical reactions, primarily between calcium and phosphates, that help a brewer establish the correct mash pH can also help him or her establish the proper boil pH. If your boil is cloudy, but large flakes of break material are not present, the problem is likely that your boil pH is too high. Adding a small amount of calcium will fix this problem most of the time. Plus, you will be able to tell if it worked by the appearance of large, fluffy flakes in your kettle.
So here’s how to hit the right boil pH in most ordinary brewing circumstances. If, after the first 15 minutes of boiling your wort, you think your boil pH is too high, add approximately 50 ppm of calcium ions to your kettle. For 5 gallons (19 L) of wort, adding 1 tsp of calcium chloride (CaCl2) or calcium sulfate (CaSO4) will yield about 50 ppm. After another 10 minutes, check your wort again — if the break material still seems like little specks as opposed to bigger flakes, add another 50 ppm of calcium.
Most of the time, you’ll see your hot break improve after the first addition. If two additions of calcium don’t work, adding more calcium is probably not going to solve the problem. Finally, if you do have a pH meter, you can also measure your wort pH in the final 15 minutes of the boil, and adjust it with acid (such as phosphoric acid) to a pH of 5.1–5.2, if needed.