Hey Yogurt-Maker, Where'd You Get Those Microbes? : The Salt Making yogurt requires bacteria — but which strains of bacteria? There are dozens to choose from, and that choice affects yogurt's tartness and texture.

Hey Yogurt-Maker, Where'd You Get Those Microbes?

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DAVID GREENE, HOST:

Now back to the food we have been learning about all week, yogurt. When you eat it, you can say I am eating something that is still alive. Yogurt is full of special bacteria. They ferment milk into something thick and slightly sour. There are old-fashioned ways to use these yogurt-making microbes, but, as NPR's Dan Charles reports, commercial yogurt-makers today are using modern science.

DAN CHARLES, BYLINE: For Atanas Valev, the taste and smell of yogurt is the taste of his homeland, Bulgaria.

ATANAS VALEV: It's just this smell of the fermented milk. And it's tart, tangy tart. That's what yogurt should taste like.

CHARLES: He's now trying to bring that taste to America. His company is called Trimona Foods. The secret to that taste, he says, is the bacteria that Bulgarian yogurt-makers selected, preserved and used for thousands of years. And when he flew to the U.S. in 1991, he brought with him in his luggage two jars of these precious bacterial cultures.

VALEV: It was a homemade yogurt in Bulgaria. It was sheep yogurt.

CHARLES: But you got it from a store? You got it from a shepherd?

VALEV: No, I got it from a shepherd.

CHARLES: He kept that yogurt and used it as a mother culture to make more for himself and his friends. It's a pretty simple process. You just add a bit of yogurt to warm milk. The bacteria multiply, consuming lactose and turning it into lactic acid. That makes the milk more acid, and eventually it sets in a gel, yogurt. But when he started making yogurt on a factory scale, he couldn't do it the old-fashioned way anymore. It would have taken a huge amount of yogurt to start each new batch. Plus, this method, called back slopping, can raise the risks of contamination. If you're in the commercial yogurt business, you need a microbe manufacturer, like the Danish company Christian Hansen. Its North American headquarters is in Milwaukee.

MIRJANA CURIC-BAWDEN: Hi.

CHARLES: Hi.

CURIC-BAWDEN: I'm Mirjana.

CHARLES: You're Mirjana. OK.

CURIC-BAWDEN: Yeah. (Laughter).

CHARLES: Good. Good to meet you.

Mirjana Curic-Bawden is an expert on yogurt-making microbes. She's a long way from home, too.

CURIC-BAWDEN: I grew up in Belgrade in Serbia, and my grandmother lived nearby the Bulgarian border, and she made yogurt by herself.

CHARLES: She moved to Denmark to study microbiology then went to work for the company Christian Hansen.

CURIC-BAWDEN: My grandmother would be really proud of me. She never understood why I had to go to school to make yogurt.

CHARLES: What grandma didn't know is that science can change the taste and texture of this food. All yogurt is made from milk plus two specific kinds of bacteria.

CURIC-BAWDEN: Streptococcus thermophilus and Lactobacillus bulgaricus.

CHARLES: But the curious thing is two brands of yogurt can be made from the same milk, the same two species of bacteria, and still taste quite different from each other. That's because of the bacteria, Curic-Bawden explains. Yes, they're all Streptococcus thermophilus and Lactobacillus bulgaricus, but they can still differ just as people do.

CURIC-BAWDEN: I mean, we are short, tall, you know, chubby or skinny.

CHARLES: And these bacteria, some of them, gobble up lactose faster than others. Some release more of that sour, tangy flavor. So her company has assembled a kind of microscopic zoo, more than 60 different strains of yogurt-making bacteria.

CURIC-BAWDEN: And we blend them in different ratio to achieve the certain texture and flavor.

CHARLES: Yogurt-makers with a particular vision for how their yogurt should taste - they can go to Curic-Bawden's company and find the bacterial blend that's just right for them.

CHARLES: And Christian Hansen then grows these microbes on a grand scale. Bacteria from this one company ferment 40 percent of all the yogurt sold in America. Max McGloughlan, one of the chemists in charge of production here, shows me 8,000-gallon tanks where the bacteria multiply, machines that concentrate them into a thick soup.

MAX MCGLOUGHLAN: After the bacteria is concentrated, we bring it over to our freezing area for pelletizing, and we make small droplets of frozen bacteria.

CHARLES: There are 100 million individual microbes in each little pellet. Each pound of pellets will make 1,000 gallons of yogurt. They leave here in big insulated boxes, a few hundred pounds of microbe pellets packed in with a few hundred pounds of dry ice. They're on their way to yogurt companies across the country. They are the living heart of the yogurt business. Dan Charles, NPR News.

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