Wine and chocolate have a lot in common that might not be obvious at first glance. Indeed, they’re a bit like a mother-daughter team: they don’t get along well because, in some ways, they’re just too darn similar. Both are concentrated sources of flavonoids (a class of polyphenol), some of the compounds that give wine its backbone, chocolate its bitterness, and both their deep red-purple color (yes, there is red-purple in chocolate, though it’s far more pronounced in unprocessed cacao than the oxidized browns of Dutched cocoa). Most of the flavonoids that give cacao its astringency degrade during fermentation—ripe cacao pods are fermented just after harvesting to help remove the pulp from the beans and to improve the beans’ flavor—but enough still remains to give finished chocolate a bit of an edge. Hence, dark chocolate with a high percentage of cocoa liqueur (and therefore relatively little sugar) has a bitterness that’s an acquired taste in much the same way that structured (think lots of polyphenols) red wines are an acquired taste for most people.
We all know that most red wine is rich in tannin, but so is chocolate. Cocoa powder actually contains more tannin than black tea. So, if you’ve ever thought that a piece of chocolate made your red wine taste more “dry,” there’s a good explanation behind your experience. Tannins, and flavones in particular, are part of what make a wine feel “dry;” they quite literally bind to the proteins that help make your saliva viscous, pull those proteins out of solution, and therefore make your mouth feel less moist. Your salivary glands constantly replenish the saliva in your mouth, but tannins still have a cumulative effect over short periods of time. If the tannins in your bite of chocolate have just precipitated some of your salivary proteins, your next sip of wine will precipitate more proteins and make your mouth feel drier than had you just sipped the wine and skipped the chocolate.