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LIANE HANSEN, host:

A few weeks ago we asked NPR correspondent Joe Palca if he'd like to contribute something science-y for our occasional series about food and cooking. Sure, he said. What about the physics and chemistry that make a souffle rise or fall? Sure, we said. So Joe Palca rose to the occasion to explain the science of beating eggs.

JOE PALCA: I like to cook and I've beaten plenty of eggs in my day. But I figured if I'm going to do a serious radio piece about beating eggs, I'm going to get the help of a serious chef. So I turned to Jeffrey Buben. He's the owner and head chef at Vidalia, a restaurant in Washington, D.C.

Mr. JEFFREY BUBEN (Chef): Okay. Well, if we want to take a recipe like a meringue or a soufflé, we're going to separate the yolks from the white. We're going to separate the fat from the protein.

PALCA: Fat and protein, remember that. The yolk has fat and some protein, but the white is all protein, no fat.

Mr. BUBEN: When I was growing up in the kitchen, the chefs would say no goldfish. And what they meant was when you separate the eggs, sometimes when you separate eggs you get a little nip of the egg yolk in the whites and that would fall into the bowl. And if you brought the chef a bowl of egg whites that had goldfish in it, or try to, you know, use those, he would pretty much throw you out of the kitchen and tell you to start all over again.

PALCA: So why is it so important to make sure there aren't any goldfish in the egg whites? Because remember, yolks have fat in them.

When you beat egg whites, you're basically mixing air into them. The protein in the egg whites forms a kind of skin around the bubbles of air. If there's any fat present, the skin can't form and the air leaks away. Even a trace of fat is ruinous. So no goldfish if you want a souffle.

Now, there are some tricks to getting just the right amount of air into your egg whites.

Mr. BUBEN: You want to make sure you have a very clean bowl. You want to make sure that your beating takes place over a nice, even flow of beating to incorporate the air. And you don't want to over-beat them and have too thick a mixture that it won't fold into your souffle or to your batter or to your sponge.

PALCA: So Jeff's ready to start. He's wearing a spotless white chef's jacket, checked pants, and those clogs that all chefs seem to favor. He's got a large, clean, stainless-steel bowl - some say copper bowls work better, but Jeff's not convinced. He's a large whisk and a carton of fresh eggs. He picks one up, holds it over his work table, and tells me something surprising.

Mr. BUBEN: You always want to crack an egg on a flat surface. What that does is it gives you less shell shatter, so that when you go to add it to a recipe, you won't get little shards of shell in your recipe. So it comes with a much cleaner crack, one crack on a flat surface.

PALCA: So not on an edge?

Mr. BUBEN: Not on an edge.

PALCA: Never knew that.

(Soundbite of banging)

PALCA: Jeff cracks open an egg and lets the white spill into one bowl. Then he plops the yolk into a different bowl. He repeats this with two more eggs.

Now, I have a little editorial note here from my editor, Allison Richards. She says if you're not as expert as Jeff Buben in separating eggs, you might want to put the white from each egg into a small bowl, inspect it for goldfish, and only then add it to your mixing bowl. Now, back to our story.

Jeff picks up his whisk and starts to work on the egg whites.

Mr. BUBEN: Now, what I like to do is start in circle eights, just to break up the egg whites. Then you want to go in a circular motion. Turn your bowl at about a 15 degree angle, and just keep whipping it, and try to get as much air in as quickly as possible.

And I have a lot of people say, we were doing a party last month, and we were whipping egg whites by hand, and they said I can't believe people still whip egg whites by hand. I said, I didn't know there was any other way.

PALCA: About four minutes later, at a steady 180 beats per minute, our egg whites have transformed.

And now you're getting something that's really creamy.

Mr. BUBEN: And what we're looking for now is nice beautiful peaks. Some chefs that I learned from say there's a point where you have the meringue perfect, is when you just lose the shine from the egg whites. And we're getting very, very close to that point as you see. The peaks are starting to come up nice and beautiful. There we have it.

PALCA: Amazing. I mean, it's just so different in texture. This is fragile still.

Mr. BUBEN: Very, very fragile, so you have to move very quickly with it and be very gentle.

PALCA: Move quickly because the air can still leak out of the tiny protein pockets, and move gently because the protein skins are thin and collapse easily.

Jeff uses his whisk to mix the egg yolks and then takes a rubber spatula and begins to gently add the stiff egg white mixture to the yolks.

Mr. BUBEN: Just barely fold until it's incorporated. And we're going to place that into a baking dish.

PALCA: And put the baking dish into a 350 degree oven for six minutes. In the oven those air bubbles trapped in the egg whites expand, making the souffle rise. The heat also causes the protein to stiffen a bit, and along with the fat from the yolk it forms a kind of scaffold that keeps the souffle from collapsing.

Mr. BUBEN: And now we're going to check on our omelet souffle. Oh, isn't that beautiful.

PALCA: The egg mixture has nearly doubled in volume.

Now, I'd probably eat it as is, but Jeff's got bigger ideas. While the souffle was in the oven he made a reduction of wine and shallots, stirred in some butter and now he spoons that mixture over the souffle, topping it off with a few shavings of black truffle.

A couple of glasses of red wine appear.

(Soundbite of glasses clinking)

Mr. BUBEN: Bon appetit.

PALCA: And you wonder why I love my job.

HANSEN: That's NPR's science correspondent Joe Palca at Vidalia Restaurant in Washington, D.C.

You can watch this lesson from Chef Jeffrey Buben on how to make the perfect souffle, and get the recipe at our Web site, NPR.org.

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