Last week we filmed the video for Craft Beer & Brewing’s upcoming online course on quick sour beers. As we were discussing some of the more technical aspects of the material, it struck me that we often use the term “pH” with abandon, but we rarely stop to really think about what it is. If, like me, some time has passed since your last chemistry class, here is a simplified way to understand pH and, more importantly, why it matters in the brewery.
Almost everyone knows that the chemical formula for water is H2O. [Ed note: Apologies to the precise among you; the system doesn’t do subscripts.] This simply means that every molecule of water consists of two hydrogen atoms and one oxygen atom. The reason that two hydrogen atoms pair up with one oxygen atom has to do with the readiness with which each is willing to either (1) part with its own electrons or (2) steal electrons from other atoms. A hydrogen atom has but one lonely electron, which it is more than willing to offload, much as one ditches one’s suitcase in the hotel room before heading down to the lobby bar for a well-deserved beer.
Oxygen, however, is a greedy little jerk. In fact, it’s twice as greedy as hydrogen is generous, which means that oxygen isn’t satisfied with just one electron: It wants two. And so, a sort of atomic ménage à trois takes place, in which two hydrogens shack up with one oxygen, thus giving us water.