The science of cheese

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Cheese: From her udder to your stomach

As the vets and vendors, the farmers and their champion cows head home from World Dairy Expo, held in Madison, Wis., The Why Files is still thinking about cheese. How is it made? Is cheesemaking a science, an art, or a mishmash of the two?


Rear view of cream-and-brown mottled cow, her udder attached to mechanical milker.

©S.V. Medaris
Where it all begins: A cow donates her milk to a vacuum-operated milking machine at the World Dairy Expo. Those white tubes carry milk to a milk tank, just as they would at a farm.

What is the cutting edge — in science, technology and marketing — of a product that could be older than written history?

In the Odyssey (800-ish BCE), Homer described the one-eyed monster Cyclops as a cheesemaker…

Cheesemaking was likely invented by people who stored milk in containers made from the stomachs of ruminant animals. These stomachs contain rennet, a mix of enzymes that coagulates solids and causes them to separate from the liquid portion of the milk.

Those solids form curd, the first stage of cheesemaking. Curds are naturally acidic, and hence slower to spoil than milk.

But what started out as a method to preserve milk has persisted and proliferated in the age of refrigeration, as many people find cheese irresistible.


Student in white lab coat and blue hair net holds scoop as white whey pours through the sieve.

Credit: The Why Files
Separating curd from the liquid whey is usually the second step in cheesemaking. This brew, being strained at the Center for Dairy Research, will become mozzarella, the archetypal pizza cheese.

We started Cheese-Quest, Why-Files edition, with a logical move: hoofing half a mile west to the dairyland within America’s Dairyland: the Center for Dairy Research at the University of Wisconsin-Madison.

We lucked out. The center, one of six funded by America’s dairy farmers, was holding its semi-annual cheese technology short course, and we sat in on a class on cheese flubups, a talk about pizza cheese, and a hands-on cheesemaking session in the University’s dairy pilot plant.


Woman uses one hand to display cooked pizza with two types of cheese.

Credit: The Why Files
Carol Chen discusses browning, blisters and flavor on pizza with a class at the Center for Dairy Research.

Cheese begins when fresh milk is acidified with chemicals or bacteria. Within hours, the milk solids coagulate into pellets called curd, and the liquid whey is drained off. The cheese may be finished within in days (fresh mozzarella), or months or even years later after a long period of ripening in a cooler (aged cheddar, for example).

The unique form and flavor of a cheese reflects the:

Choice of milk: from cow, goat or sheep

Geography: where the cow’s feed was grown

Bacteria: strains can be blended for a specific process and desired flavor

Salt: for flavor and preservation

Soaking in brine: to form a protective rind

Aging and mold (as in blue cheese): to enhance flavor

Total, per-capita U.S. cheese consumption

Line graph showing in consumption of mozzarella, parmesan, Swiss, other cheeses. Total 2008 consumption about 35 pounds.

In the United States, slightly more exotic cheeses are gaining, as is overall consumption.

A biological product

Cheese resists the standardization of the assembly line. “Why doesn’t the cheese from a given factory taste the same week after week, year after year?” asks Dean Sommer, director of cheese technology at the Center for Dairy Research. “Why does cheddar from factory A taste so different from cheddar from factory B? It’s because cheesemaking is a biological process, and there are so many variables.”

Local weather and soil chemistry affect the feed, and feed affects the taste of the milk, so local conditions matter, says Sommer, and cheddar has a different taste on the East Coast, Midwest and West Coast. On the West Coast, cows eat a high ratio of vegetable scraps from large California farms. “In the Midwest, most dairies are feeding total mixed ration, a mix of three to six different types of food; it might be hay, corn silage, cottonseed, some brewer grains. It depends on which ingredients are cheap and available, every farmer does it differently, so the feed is different.”


Students spaced across room use hands to support yards-long strand of cheese.

Photo: The Why Files
Like a warm, white anaconda, fresh-extruded mozzarella emerges while a furtive cheesemaker sneaks a mouthful of the young cheese.

All these variations are reflected in the flavor of the cheese. “It’s similar to the concept of terroir [local taste determined by local conditions] in winemaking,” Sommer says. “In Switzerland, cows eat mountain flowers in the meadows in the summer, and those flavors come through in their cheese.”

Viva la difference!

While local variations are a problem for big producers, they are stock-in-trade for artisan cheesemakers. “In the ’80s, the industry mentality favored standardization; it was like the Big Mac, which should taste the same everywhere,” says Sommer, who once worked for a giant cheesemaker. “Today people want the ability to create a unique flavor that is different from the cheese factory down the road.”

While large dairy farms still rely on total mixed ration, the danger of erosion in hilly regions forces farmers to use more grazing, and the result is more flavorful milk, and more distinctive cheese.

New cheesemakers and new flavors have helped to save the Wisconsin dairy industry, says Sommer. “Twenty years ago we were heading down the dead-end road of commodity cheese, now we’ve gone into specialties that leverage the craftsmanship and heritage of the people, and our terroir, and that is why the industry is healthy and optimistic. Twenty years ago, the attitude was, ‘Last one out of the dairy industry please turn out the lights. Today you don’t hear that.'”


Brown cows with bells on, rest on the top of a grassy ridge, snow-covered Alps in the background

In hilly or mountainous areas, terrain may be too steep for growing crops. Cheesemakers say that grazing, such as these Brown Swiss cows in Switzerland, produces milk with more flavor than feeding corn and other row crops.

Bold bacteria to the rescue?

Multiple recipes can be used to make cheese, with variations in temperature, chemistry or timing, says Sommer. “Even if you start with the same milk, and end up at the same place compositionally, from a flavor standpoint the result can be different.”

Cheese is a biological product, and the taste reflects its living ingredient: the bacteria that initiate acidification and then confer flavor. Thousands of strains of bacteria are on the market, “and they all make slightly different flavors,” Sommer says. And that’s not even counting the bacteria that arrive in the milk or sneak aboard in the cheese factory. “Without those other bacteria, cheese would be very mild,” says Mark Johnson, a scientists with the Center for Dairy Research.


Two gloved hands lift rough cylinder of aged cheese

This cheddar, almost two years old, came from the Bleu Mont Dairy in Blue Mounds, Wis.

By analyzing DNA, Johnson has identified bacteria in cheese, and found up to a dozen strains — most of them accidental. “Usually, up to three strains are added, and everything else is native to the environment, the plant, or the milk,” Sommer says.

Johnson is a microbiologist by training, and if he detect better strains of these hitchhiking bacteria, he will check if they can accelerate curing. “One goal is to get the desired flavor fast, so you could put out the cheese at three months and it would have a unique character without the expense of aging.”

On the flip side, finding funky strains that make off flavors could help in their elimination.

Going for flavor

Because cheese is a high-calorie food that normally contains considerable sodium, a factor in high blood pressure, the industry faces rising concerns about and obesity and hypertension.

Youth obesity is soaring, so the issue is germane to school lunches, but cheese has real benefits, Johnson says. “People forget the protein, and especially the calcium, phosphate and potassium. The balance of calcium and phosphate is perfect for growing bone. If you take cheese off the [school-lunch] menu, you are going to deprive kids of these needed nutrients.”

The challenge, he says, is to lose the negatives while keeping the benefits — and the flavor. “We want to provide what kids like, to give the nutrition without the downside. Kids like a buttery flavor, but when you remove fat and sodium, you remove butteriness, the sweet character.”

Johnson sees progress in the flavor quest. “I have a low-sodium cheese aged nine months. At three months, people could tell it was low sodium, but at nine months, they could not. Bacteria are doing something in the cheese to make it taste so you would never say it lacked salt.”


Bar chart: Greece and France have high per capita cheese consumption, China and Egypt are low

Cheese is mainly eaten in Europe and the Americas. The uneven consumption represents export markets for producers.

Close up of cheddar cheese chunk showing cracks

Courtesy Mark Johnson
Bacteria created gas and those slits in this cheddar cheese. If the flavor is good, this cheese will become processed cheese; but gas formation still cuts industry profits.

When good cheese goes bad

Pity the diligent cheesemaker. Johnson says plenty of problems arise after good cheese has left the dairy. Excess acidity in cheeses like cheddar and Colby turn it brittle, grainy and bitter.

Bad flavors in the milk, which can result when the cows eat a strong flavor like wild onion, can cause off-flavors, especially in raw milk cheese. A “barny” odor — uncomfortably close to cat urine — can result from protein degradation or wild strains of lactobacillus. (Unlike most bacteria, lactobacillus, the group of bacteria used to make cheese and yogurt, can survive in acidic milk.)


Man pulls apart long strings of white cheese as students observe

Photo: The Why Files
It stretches! Dean Sommer, of the Center for Dairy Research, checks the stretch on some brand-new mozzarella cheese. Mozzarella gets its rubber-bandiness as the curd is mixed and proteins link together.

Exposure to display-case lighting is another problem, and is one cause of “temperature abuse,” failing to hold the cheese between 35° and 45°F. High temperatures can lead to oil separation, loss of flavor and bitterness. “50° and above is hot for cheese, and 70° will destroy it,” says Sommer, who has seen even hotter cheese in store displays. “It was warm to the touch.”

Teaching the wrong lesson?

High temperatures are a problem “throughout the distribution system and also for importers who bring cheese in from Europe,” says Sommer. At a cheese plant in Philadelphia, the cheese was unloaded 12 months a year on an asphalt parking lot, which may work fine in February…

Many problem strike after the cheese has left the factory, Sommer notes. “I feel bad for a lot of cheesemakers. They put their heart and soul into the cheese, but it can get abused and turn awful, and the consumer buys it and probably blames the cheesemaker. They put their label on it, but it was fine when it left their door.”

Sommer thinks such degradation has an insidious cost. “I’ve bought cheese and given it to friends. I can’t swallow it, but they say, ‘It’s okay.’ We are teaching people that cheese should taste like lard or wet cardboard. I don’t think anybody in the industry has a handle on how much cheese sales have declined because people get turned off and won’t return.”

— David J. Tenenbaum


Terry Devitt, editor; Emily Eggleston, project assistant; S.V. Medaris, designer/illustrator; David J. Tenenbaum, feature writer; Amy Toburen, content development executive