I haven't had coffee today.

REGINA BARBER, BYLINE: (Laughter). You should leave that in.

KWONG: You're listening to SHORT WAVE from NPR.

Hey, everyone. It's co-host Emily Kwong.

BARBER: And Regina Barber, scientist in residence.

KWONG: Gina B., I figured out something we share in common.

BARBER: Is it that we both think Loki is way more interesting than Thor?

KWONG: That is true. That's facts. It's not that. It's that we both grew up near hubs of coffee culture, I realized - New York City for me and Seattle for you.

BARBER: Yeah, yeah, that's true. But can I tell you a secret? And it's not really a secret for people who know me, but...

KWONG: Oh, no. What is it?

BARBER: I know very little about coffee. I actually can't handle the caffeine because I'm such an energetic person. I'm...

KWONG: Oh, yeah, yeah, yeah.

BARBER: I'm more of a green tea drinker. I always have been.

KWONG: Yes, coffee is a potent drink. Growing up for me, it was this, like bitter, hissing thing that my dad would make for breakfast, and I thought it tasted like poison.

KWONG: But now I am really into coffee. I love the smell of the beans. I love pulling espresso shots, just making that perfect cup for a friend. And in these many pandemic days, it's been the drink that got me through, you know, the only ritual I could maintain when I couldn't get out of bed in the morning.

BARBER: Tell me more because for me, it was the soothing tea with, like, a touch of caffeine that got me ready to start the day. That...

BARBER: That's my ritual. But I'm...

BARBER: ...Aware other people like you - like, they need coffee.

KWONG: And if you, SHORT WAVER, are in need of a pick-me-up. we're coming in hot. Today on the show, how to brew the perfect cup of C8H10N402.

BARBER: Did you just name the chemical formula for caffeine?

KWONG: I saw what I said. You're listening to SHORT WAVE, the daily science podcast from NPR.

BARBER: All right, Emily Kwong, today we're talking about the science that drives home coffee brewing, which I'm guessing is that sound I'm just listening to.

KWONG: It is my alarm clock. It's the sound that reliably gets me out of bed in the morning. And it is the sound of coffee beans being pulverized into a powder for brewing. I admit I am this coffee motivated. And in the past, I drank way too much. Now I've scaled back, and it's actually become a source of more pleasure. I started buying whole beans, grinding them at home, and it's just transformed the experience. I drink less coffee, and I enjoy it so much more.

BARBER: I actually love the smell of coffee, but otherwise I can't relate.

KWONG: You know who does relate, though? Sam Spillman. Both of her parents were heavy coffee drinkers.

SAM SPILLMAN: My mom, even if we were running late - we had to stop by, like, a coffee stand to get coffee in the morning. And she'd always get me a granita, like, a blended coffee drink. I was way too young, but it's fine.

KWONG: Sam is the director of coffee and customer experience at Caffe Vita, a coffee roaster in Seattle that works directly with coffee farms. At 13, Sam told her, mom, I want to be a barista. And she got so good at coffee making that she won the 2019 United States Barista Championship, which is, like, the industry's highest honor.

BARBER: Whoa. So she's, like, really exceptional at everything coffee.

KWONG: She is. And I think it's because she approaches it in a super technical way. Sam studied engineering. She thrived in math class.

KWONG: And she says that understanding the more scientific side of coffee is what allows her to create these, like, elevated experiences. And she is very, very clear about this. You don't need fancy machines or beans to do it.

SPILLMAN: I think that you can really get a good cup of coffee no matter what device you're using. It's just how you use the device.

BARBER: OK, Em, let's back up a little bit. Can we explain what even is coffee? Like, there's so many kinds and different ways to brew it.

KWONG: Yeah. So technically, coffee is a cherry.

BARBER: Oh, my God. I love cherries.

KWONG: Me, too. Now my favorite cherry is coffee. So these cherries - they are the fruit of a woody, evergreen plant which grows closer to the equator.

BARBER: OK, so that's why there's a lot of coffee beans that come from Central or South America and parts of Africa and Asia.

KWONG: Yeah. There's actually a Coffee Belt, a bean belt of coffee farms, that is right between the Tropic of Capricorn and the Tropic of Cancer. And these cherries have the beans inside. Here is a picture of it.

BARBER: OK. You know, it does look like a cherry. And the coffee bean inside looks a bit watery. It almost looks like, kind of like a grape in the middle?

KWONG: Yeah, it's got, like, liquid inside. And this - the bean...

KWONG: ...Itself, if you were to, like, pop it out and just eat it, tastes, I've heard, kind of grassy or woodsy. The flavor only comes from roasting. That's a really important part of the coffee process because it brings out all the natural sugars and acids of the bean. Now, between the two extremes of roasting, like, a light roast coffee bean versus a dark roast, let it be known a lighter roast does have more caffeine in it when measured by volume.

BARBER: So I should be ordering dark roast because of my caffeine intolerance.

KWONG: Yeah. Yeah. Technically, yes. Sam explained the roasting is inducing this thing called the Maillard reaction. That's that chemical process between amino acids and sugars that gives bread its golden hue. Too much Maillard in your coffee roasting gives excess carbons to your beans and that bitter taste that some people love in a dark roast, but you're subsequently losing a lot of the sugars and the acids and, yeah, the caffeine that makes coffee perky.

KWONG: Sam feels so strongly about this that she convinced her dad to try a light roast once.

SPILLMAN: And about 30 minutes later, he's like, I feel yacked (ph).

SPILLMAN: Like, I don't know what's happening. Like, I've never experienced this caffeine before. I'm, like, see - I'm telling you, like those darker-roast coffees, you're losing so much of the caffeine. And you're getting, like, this very bitter, dry, lacking complexity drinking experience.

KWONG: By the way, no shame to people who like dry roasts. It's fine. It's just something to watch out for because if the beans are over-roasted, you'll know because it will taste way too bitter and because the beans themselves will be oily. Like, they'll have this shiny slick outside. And it means that the cell wall has totally broken down.

BARBER: I'm learning so much. OK, so as a noncoffee drinker, I don't have any equipment at home. Like...

BARBER: ...I only have, like, one of those giant water boilers for my tea. But let's say I wanted to get a regular, old coffee maker so when friends come over, I can make them some coffee? How do I maximize the taste?

KWONG: Regina, there's so much you can do if you can get your hands on a grinder and some whole coffee beans. So when you grind the coffee, you'll have the grounds, and they're not going to dissolve completely in water. Only 30% of the coffee bean actually dissolves.

KWONG: And it will dissolve in a few stages. The first thing that comes out in the water when you're brewing is its acidic properties. Then comes a wave of fats and melanoidins from the Maillard reaction. The last to dissolve are the carbohydrates. So taste wise, the narrative arc is sour, sweet, bitter.

SPILLMAN: And so we're trying to highlight that sweetness in the center, while having a little bit of the sour and the bitter to balance it out.

KWONG: So think back to chemistry class, Regina, OK? The smaller the ground...

BARBER: I am so bad at chemistry.

KWONG: That's fine. That's fine. This is basic, basic stuff.

KWONG: The smaller the grounds, the easier it is to dissolve, right?

KWONG: You want a texture that's kind of like fine sugar.

KWONG: And that's good if you're making especially, like, a espresso.

KWONG: Bigger grounds the size of, say, ground pepper - they're a bit harder to dissolve. And that's really good for a French press. That's where the coffee drink is mixing with the grounds in that container. And you don't want it dissolving too much, because then it just gets overbrewed and bitter.

BARBER: OK. And for a drip pot?

KWONG: Yeah. Like, if you were to buy a coffee pot for yourself, you would want to go for...

KWONG: ...Your ground size to be something in the middle.

BARBER: OK. So, like, the size of, like, table salt?

KWONG: Exactly. You can look at it with your eyes in the palm of your hand. But the best way, honestly, is through taste. Like, brew...

KWONG: ...Yourself a cup of coffee, take a little - (imitating sipping noise) - sip, and if it's too sour, make your grinds smaller.

KWONG: If it's too bitter, make your grinds bigger. From there, it is all about controlling for variables. So like, the amount of time the water is hanging out with those grounds, the contact time, or the water temperature. The barista standard for best coffee water temp is between 195 and 205 degrees Fahrenheit.

BARBER: OK, so like, if you have a French press, you want to heat your water to that temperature.

KWONG: Yeah. And if you have a drip pot, Sam says one really easy way to glow up your morning coffee is to actually take out that little paper filter and pre-wet it...

KWONG: ...So that the coffee doesn't have a paper taste.

BARBER: I am loving, actually, all these tips. But also - and I mean this with love - I used to think coffee brewing and people being obsessed with it was a bit pretentious.

KWONG: Are you accusing me of being a coffee snob?

BARBER: Not anymore. You've changed me. You've converted me.

KWONG: No, it's cool. It's cool. It's coffee. You know, coffee is - it is becoming a bit like wine.

KWONG: And here's a secret. Those flavor notes on the coffee bag, you know, where it says, like, toffee and mango? Those aren't ingredients added to the coffee.

SPILLMAN: You'll see really wild coffees that have, like, fruit punch and cranberry and, like, all these different flavors. Those are just, like, the taste experience of the coffee that the roasters experienced of that coffee.

KWONG: Shame on you all.

BARBER: I agree with you, Em, but it seems to be working.

KWONG: And for Sam, her obsession with making the perfect cup of coffee is not coming from a place of pretension. It's coming from a place of respect and excellence for her craft, for the farmers, for the product and for this amazing plant made by nature.

SPILLMAN: It's truly an honor - and I didn't take this lightly in competition - of I am the final stage. Like, I'm the final step to creating this experience for those judges. And I wanted to bring that experience to the table of not just with how I'm brewing the coffee but where that coffee's coming from, why it is the way it is, and this shared goal of perfection.

BARBER: That was a lesson for me. I like a coffee lesson.

KWONG: I am so glad, my friend.

BARBER: Before we head out, a quick shout out to our SHORT WAVE+ listeners. We appreciate you and thank you for being a subscriber. SHORT WAVE+ helps support our show. And if you're a regular listener, we'd love for you to join so you can enjoy the show without sponsor interruptions. Find out more at plus.npr.org/shortwave.

KWONG: This episode was produced by Chloee Weiner and edited by Rebecca Ramirez. Rachel Carlson checked the facts. Stu Rushfield was the audio engineer. Gisele Grayson is our senior supervising editor. Andrea Kissack is the head of the science desk. Edith Chapin is vice president and executive editor at large. Terence Samuel is vice president and executive editor. And Nancy Barnes is our senior vice president of news. I'm Emily Kwong. Thank you so much for listening to SHORT WAVE, the daily coffee cast from NPR.

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