Why is there an expiration date on sour cream? –Al Malmberg, Colorado Springs, Colorado
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But that’s not how it works. (Surely you suspected this.) It’s true they start with light cream or the equivalent. Having pasteurized it, which kills most of the microorganisms that make raw milk go sour, they then dump in a special bacterial culture that produces lactic acid. If I know my bacteria–and I did stand in line once at a Kiss concert–they produce the lactic acid by excreting it, which you then pay to eat. No accounting for it, though as I look back it does explain the onetime popularity of est. Chilling the sour cream after the bacteria have had 12 to 16 hours to do their thing halts the “ripening” (i.e., souring) process, resulting in a product that’s merely tangy rather than rank. But bacterial action doesn’t totally stop, and if the sour cream sits around long enough it will eventually become so sour (or moldy) that it’s inedible. The same will happen to virtually any dairy product, since some sour-inducing microorganisms invariably survive pasteurization. Thus the expiration dates. We may think of sour cream, therefore, as occupying the bracingly tart but brief interval separating the hopelessly bland from the unspeakably vile. A perfect analogy to the positions on the cultural continuum occupied by Barney the Dinosaur, myself, and Howard Stern.
Two questions. (1) Why do you blow on hot coffee to cool it, but you blow on your hands in winter to warm them up? (2) How come vegetables have no fat, but vegetable oil is 100 percent fat? –Dick Wolfsie, WIBC, Indianapolis
