pH in brewing

Ken writes:

In another installment in my recent ‘studying for the exam series’ I thought I try to say something about the effects of pH in brewing. pH if you’ll remember is the measure of acidity and alkalinity in a solution. I think it actually stands for a measure of the concentration of hydrogen cations (protons) in the solution. The more acidic something is, the lower its pH (though it cannot go below zero) and the more alkaline something is the higher its pH (up to a maximum of 14). Water is pH7, which is neutral. Beer is acidic, typically pH 4.5 or less. This is one of the reasons beer doesn’t support the growth of pathogenic bacteria (along with the fact that it is mildly alcoholic, has very little dissolved oxygen, has antibacterial hop compounds and that yeast have already consumed most of the carbon sources pathogenic bacteria might have fed on).

Anyway, the story of pH in beer is one of steady acidification. After all, water is pH neutral or ever so slightly alkaline, so it must be a story of acidification. Beer becomes more acid at every step in the process. Calcium Ca2+ ions lower the mash pH because it reacts with phsophates in the malt forming a precipitate in a reaction that ends up with surplus protons floating about. Every hundred parts per million of calcium lowers pH by 0.4.
Furthermore, melanoidins in the malt, from dark grains like roasted barley, chocolate or crystal malt, are acidic and also lower the pH. Boiling lowers ph through the same calcium reactions as during mashing and also through reactions with polypeptides. And fermentation lowers ph. Yeast releases organic acids during fermentation (some of which it takes back up again at the end of fermentation but not all).

The ideal mash pH is around 5.3-5.4. Mash enzymes work most effectively at certain pH levels and the optimum levels for the amylolytic enzymes are 5.3 for alpha amylase, 5.0-5.3 for beta amylase, and 5.0-5.5 for limit dextrinase. Maybe the mash could go a bit lower, but the pH drops again during the boil and we don’t want to miss the optimum pH during the boil. Low pH during the boil improves ‘hot break’ formation, which is the precipitation of proteins and polyphenol which can then be removed from the beer leaving brighter less turbid wort. Proteins are least soluble at their isoelectric point, which is pH 5.2, so they come out of solution best at that point. low pH also darkens wort colour (or may be a consequence of darkening wort colour since colour is a matter of melanoidins and these are acidic…I’m not sure).

The down side of low pH is that hops are used less efficiently. The bittering compounds in hops have to be isomerised because they are not water, wort or beer soluble in their normal state. This happens at high temperature which is why hops must be added to the boil. But the rate of isomerisation is highest at pH 9 (mildly alkaline). Another downside of acid beer is that it can give you caries if you drink to much, but if you drink too much beer, caries are probably the least of your worries.

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