Consider the words used to describe the character acidity may add to a particular wine. One with pronounced acidity is described as bright. One with acidity but little substance is thin, and one with very high acidity and little fruit flavor is austere. A soft wine has low acidity, a flabby one even less.
Sometimes the same descriptors are appropriate to use with beer, particularly those flavored with fruit and ones categorized as sour or wild. They are only a starting point, just as are the measurements brewers take to indicate the level of acidity in a particular beer. Here’s how Ehren Schmidt, the “Sour Scientist” at Toolbox Brewing in north San Diego County, characterizes two of them: potential of hydrogen (pH) and tritratable acidity (TA): “pH is the first look, peeking in the window. TA is really putting it under a microscope.”
pH (a measure of the power of an acid in solution) measurements, of course, are used in scores of industries and throughout the brewing process, for both sour and “clean” beers. In a sentence, it is expressed on a logarithmic scale (so that a change of one pH unit corresponds to a tenfold change in concentration) with numbers below 7 more acidic than pure water, those above more alkaline. pH measures only disassociated hydrogen, but the organic acids in fermentation are weak acids and do not disassociate as easily as strong acids. TA (a measurement of volume of acid in solution) measures both associated and disassociated hydrogen. It is not the same as total acidity (although both are referred to as TA), which is harder to measure, but it is a good approximation in both beer and wine.