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Experts Percolate on How To Brew Coffee


And Flora Lichtman is here with our Video Pick of the Week. Hi, Flora.

FLORA LICHTMAN, BYLINE: Hi. It's multitasking's - you know, what goes best with multitasking? A big cup of coffee.


LICHTMAN: That's what our video is about this week. Our continuing coverage of this hard-hitting serious issue: What is the science in your morning joe? So our video this week was put together by video producer Jenny Woodward. And this one goes into the gear.

FLATOW: The gear?

LICHTMAN: The gadgets for serious, really serious coffee drinkers. So you may have seen these before in this fancy schmancy places like we went, Everyman Espresso in New York City. You know, the Woodneck, the Chemex, and it's like microscopes. You know, you wouldn't use your scanning electron when you really needed a confocal.

FLATOW: Of course not.


LICHTMAN: That's what the baristas will tell you, anyway. So you can look at our video and find out, you know, which tools give you different flavors and aspects to your coffee.

FLATOW: Yeah. It's a great video because not only does it explain which of these fancy coffee makers do what, but it also explains how the coffee is affected by how long it's in contact with the beans, the size of the beans.

LICHTMAN: Right. So this is something I didn't know. The reason why you want to have evenly ground coffee so all the little particles are the same size is because you're doing an extraction. It's just a little chemistry experiment in your coffee maker. And if the particles are smaller, you have more surface area to the amount of - to the particle, and they extract faster, and you get the kind of yucky flavors that come out with a longer extraction.

FLATOW: This is SCIENCE FRIDAY from NPR. I'm Ira Flatow here with Flora Lichtman talking about her coffee experiment, sort of. You compared a lot of different coffees in this video, right?

LICHTMAN: We looked at a lot of different - we looked at...

FLATOW: Coffee drinkers.

LICHTMAN: ...a lot of different tools. And we spoke with Harold McGee, who has written a lot about food and science. And he gave us a lot of a-ha's in this video. And I think we have a clip of one that we could play. And this was something that I didn't even know to wonder about until he mentioned it, which is when you take coffee grounds and you pour hot water over them, you may have noticed that they bubble a little bit. Have you ever seen this?

FLATOW: Yeah, all the time. Yeah.

LICHTMAN: So I've seen it too, but I never thought to ask why. But Harold has the answer for us.

HAROLD MCGEE: The reason for that is that one of the products of the roasting process is carbon dioxide. In fact, the beans pop like popcorn during the roasting process. They enlarge in size. They become porous and brittle. And in all those pores is lots and lots of carbon dioxide gas, which is what caused them to pop in the first place - the creation and expansion of that gas.

And that CO2 is locked into the pore structure of the beans. So if you grind the beans up freshly, then of course you break up a lot of those pores but there are still some that are there. And you pour the water on, and that CO2 then bursts through and forms lots and lots of bubbles.

If you've ground the coffee days or weeks or months ahead of time, then most of that CO2 is dissipated, and you pour the same hot water on and it just sits there. It's not as lively. So that's one good way of telling how fresh your coffee is.

FLATOW: That's great. You know, the reason why you don't see it these days is because you put your grounds into a machine. Back in the old days, before you were born, we had these Melitas - remember, they used to take a hot pot of water and pour into a cone of coffee.

LICHTMAN: It's coming back, Ira.

FLATOW: Like vinyl records.

LICHTMAN: Bell-bottoms.


FLATOW: And you'd watch it foam up all the time, and this is the first time in 30 years I've heard a great explanation for that.

LICHTMAN: Yeah. It's like the fizz in your soda. I never knew.

FLATOW: Yeah, yeah. And it's up there on our Video Pick of the Week. Great explanation, a great video. It's up there on our website. If you want to see, maybe you're shopping for another coffee maker, right, and you want to compare the brands, and there are so many different ways.

LICHTMAN: That's right.

FLATOW: One thing that was missing is that French press.


FLATOW: The French press was not included.

LICHTMAN: Thank you for bringing this up. I asked about the French press, because I used to have a French press, which may give you some indication of what we heard. But apparently the French press is totally poo-pooed by, well, anyway by the baristas we talked to. They were like, we wouldn't even put it up on our list of tools.

FLATOW: No kidding.

LICHTMAN: No, because I think it's very hard to get an even extraction. You need the even particle size, and then to get the timing right, because you're just letting it sit there, is challenging.

FLATOW: It's amazing. And you learn about all the timing, about how long the water should be in contact with the grounds and things like that, on the website up there on sciencefriday...

LICHTMAN: There's a whole series.

FLATOW: A whole coffee series.

LICHTMAN: You could spend many minutes.

FLATOW: Yeah. Multitasking over the coffee.


FLATOW: Thank you, Flora.

LICHTMAN: Thanks, Ira.

FLATOW: Flora Lichtman - it's up there in our Video Pick of the Week and out there all with our - all of our hundreds of other videos that Flora has put together. That's about all the time we have for now. Transcript provided by NPR, Copyright NPR.