Speaker 1: Welcome to brain stuff from how stuff works, Hey, brain stuff,
Speaker 1: Lauren vocal bomb here. Hot coffee is supposed to be hot.
Speaker 1: Cold coffee is supposed to be cold, and that's the deal.
Speaker 1: It's pretty simple. The problem, then, with hot coffee is
Speaker 1: that you can't drink the whole cup while it's at
Speaker 1: the optimal temperature unless you're willing to really guzzle it.
Speaker 1: So when it gets cold, you've got a few choices.
Speaker 1: Drink it cold, reheat it, or just pour that cup
Speaker 1: down the drain and start over with a fresh pot.
Speaker 1: All three of these approaches are either perfectly fine or
Speaker 1: completely barbaric, depending on whom you ask to Some hot
Speaker 1: coffee that's gone cold is revolting to others. The reheating
Speaker 1: process renders it completely undrinkable, but that doesn't stop us
Speaker 1: from occasionally popping a cup of nine hour old office
Speaker 1: Joe into the microwave at four pm to power through
Speaker 1: until bedtime out of some combination of desperation and mild masochism.
Speaker 1: Research into why heating this humble drink is pretty much
Speaker 1: non existent, but it most likely has to do with
Speaker 1: our sense of smell. Humans aren't great at separating our
Speaker 1: gustatory that's taste and olfactory that smell responses, and coffee
Speaker 1: has aromas and flavors that hit all five of the
Speaker 1: tastes that can be picked up by your tongue and
Speaker 1: other mouth and nasal passage nerves. Sweet, salty, bitter, sour,
Speaker 1: and savory. So your personal sense of smell has a
Speaker 1: lot to do with how coffee tastes to you, whatever
Speaker 1: it's temperature, and however that temperature was achieved. That's because
Speaker 1: the chemical makeup of coffee is astoundingly complex. Even though
Speaker 1: its reputation relies heavily on the presence of caffeine, coffee
Speaker 1: gets its flavor from around a thousand different chemical compounds. Also,
Speaker 1: the final flavor of the coffee you enjoyed this morning
Speaker 1: was the product of a dizzy ng array of variables,
Speaker 1: including the temperature and weather conditions the beans grew under,
Speaker 1: when the beans were harvested, how they were dried, stored,
Speaker 1: and roasted, and how they were ground and brewed. So
Speaker 1: while the compound three methyl mutinol might make your cup
Speaker 1: of joe taste a little caramel like and ethyl no,
Speaker 1: it may give it some fruity or notes. Each step
Speaker 1: of the process either brings out or suppresses any one
Speaker 1: of these aromatic compounds differently, which brings us to reheating.
Speaker 1: We spoke with Christopher Hendon, a postdoctoral fellow at the
Speaker 1: Chemistry Department at m I T and author of Water
Speaker 1: for Coffee, a book about how coffee interacts with water.
Speaker 1: He said, reheating coffee in principle can be an absolutely
Speaker 1: fine approach to achieving a tasty beverage. In practice, this
Speaker 1: is not usually observed because people reheat in ways that
Speaker 1: promote the loss of delicious volatile compounds, and so the
Speaker 1: process of heating, cooling, and heating again drives smelling and
Speaker 1: tasty compounds out of the cup. According to Hendon, coffee
Speaker 1: experts seem to prefer a drink that has been brewed
Speaker 1: within the previous five to twenty minutes. It turns out
Speaker 1: most people for the coffee as it cools to around
Speaker 1: a hundred and fifty degrees fahrenheit that's sixty five degrees celsius.
Speaker 1: This has to do with the way our taste pathways
Speaker 1: respond to temperature in our food. But when we put
Speaker 1: something in our mouth that's too hot or too cold,
Speaker 1: we can't detect all of the compounds that contribute to
Speaker 1: its flavor. Since coffee has loads of these compounds, the
Speaker 1: temperature of the drink can affect the taste. Brewing the
Speaker 1: coffee brings out certain aromatic compounds, but whether the cooling
Speaker 1: process changes the chemistry seems to be controversial. Pendon says
Speaker 1: it is absolutely benign, while others claim it makes the
Speaker 1: drink more acidic as the coffee is exposed to air
Speaker 1: and oxidizes. Reheating coffee to the same temperature it was
Speaker 1: when it was first brewed might help you reach that
Speaker 1: sweet spot temperature wise, but it also has the potential
Speaker 1: to cause additional chemical reactions that further alter the flavor.
Speaker 1: And if you're reheating coffee that already has milk or
Speaker 1: sugar in it, that's even more in the way of flavors, proteins, chemicals,
Speaker 1: and compounds to contend with. So although many coffee connoisseurs
Speaker 1: will tell you it's a lost cause once your coffee
Speaker 1: goes cold, others say it's just important to reheat your
Speaker 1: coffee as slowly as you can in order to prevent
Speaker 1: additional chemical reactions. But if you're reheating in the microwave,
Speaker 1: don't worry about ghosts of past foods heated in that
Speaker 1: microwave coming back to haunt your coffee. And and said,
Speaker 1: the concentration of the volatile chemical composition of say, splattered
Speaker 1: pasta sauce, is pretty low, so I would be surprised
Speaker 1: if we could attribute the bad taste of microwaved coffee
Speaker 1: to only that. Our advice crank your microwave's power down
Speaker 1: to or lower and sap your cup of coffee in
Speaker 1: thirty second intervals to prevent disaster. But of course we
Speaker 1: encourage you to run your own experiments. Today's episode was
Speaker 1: written by Jesselyn Shields and produced by Tyler Clang. For
Speaker 1: more on this and lots of other tasty topics, visit
Speaker 1: our home planet, how stuff works dot com.