When it comes to food science, Harold McGee is the go-to guy—his book On Food and Cooking: The Science and Lore of the Kitchen, first published in 1984, is a certified classic, and he’s more recently become a regular contributor to Lucky Peach, delving into topics such what happens when you age canned goods passed their use-by date.

If you’re a coffee nerd, you’ll want to check out his interview on NPR about the chemistry of coffee. He touches on some neat stuff, like what changes coffee beans go through as they move through the stages of harvesting, roasting, and brewing, as well as why we enjoy bitterness even though we have evolved to find it unpleasant.

To the latter point, here’s a particularly interesting exchange about caffeine:

NPR: Do you think that caffeine is bitter? Does that mean caffeine has a flavor itself?

MCGEE: Yes. Yes, indeed. Caffeine is – it’s an alkaloid. And we find, humans, that is, find almost all alkaloids bitter. And the biological thinking about that is that almost alkaloids are also toxic, and our bitter taste, which is an intrinsically unpleasant experience, bitterness is way of warning us that there is something in whatever we’ve put in our mouth that is likely to be bad for us. Now, you might say, well, but we love caffeine because it does wonderful things for our attentiveness and wakefulness and so on. And that’s true to a certain point.

But if you have too much caffeine, it will, in fact, be toxic. So bitterness is a flavor that we learned to enjoy in the course of our lives because we can associate it with desirable things like the delicious flavors of coffee and the stimulating effects of coffee. But initially it’s an unpleasant experience.

[via NPR]