Answer Man

Answer Man: Chewing the fat over skimmed milk

Q. Your recent answer about pasteurized milk reminded me of a question I’ve long wondered about: How do they produce reduced-fat milks, e.g., 2 percent, skim, etc.?

— D.F., of O’Fallon

A. Seems simple enough to me. Just put ol’ Bossy on a treadmill. The more fat you want out of the milk, the faster you dial up the treadmill to slim her down.

OK, maybe that’s the way Oliver Douglas would have tried it on “Green Acres,” but, of course, that’s not the way it’s done in real life. Instead, the production of reduced-fat milks has evolved into a scientific process involving large centrifuges and instruments that can measure fat content precisely .

Traditionally, the moo juice was simply allowed to sit after milking, which allowed the fat to rise to the top. This fat was skimmed to make butter and cheese products, while the remaining liquid was consumed or processed into other foods.

Now, of course, that would be much too time-consuming, so modern dairies have mechanized the process. Most, like Clover Stornetta Farms in California, use a centrifuge.

“It spins,” a spokeswoman explained. “The fat is lighter than the skim milk portion, so the cream (rises) to the top of the centrifuge and the skim goes out the bottom via pipes.”

Kimberlee Burrington, the dairy ingredients applications coordinator at the Center for Dairy Research at the University of Wisconsin, once described it this way: Inside the machine is a series of discs with vertically aligned holes stacked together. These discs spin at high speed. The fat moves inward in the separator and the skim milk moves outward. It is a physical separation based on the difference between the density of the fat versus the skim milk.

The amount of fat removed is controlled in various ways. Sometimes metering pumps determine the amounts of skim milk, cream and other products that have to be recombined before being pumped into the pasteurizers. Other dairies use sophisticated computerized setups that carefully monitor how much cream and fat are being taken out to produce milk with various percentages of fat.

The result are the products you see on your store shelves. The average composition of your high-octane milk is 87.2 percent water, 3.7 percent fat, 3.5 percent protein, 4.9 percent lactose and a trace of ash, although this varies by breed, feed and other factors. Skim milk contains no more than a half percent butterfat while low-fat may range from a half percent to 2 percent fat.

But here’s a stunner for all you weight-watchers: Last year, the prestigious Journal of the American Medical Association Pediatrics argued that making children drink skim or low-fat milk may not help them avoid obesity even though it contains fewer calories. In fact, it actually may produce more pounds and heart disease.

Surprised? Maybe you shouldn’t be if you think about it, say Dr. Walter Willett, who heads the department of nutrition and epidemiology at Harvard, and Dr. David Ludwig, director of the obesity center at Boston Children’s Hospital.

For starters, since low-fat milk contains fewer calories and are less filling, children may make up the deficit by eating or drinking even more than they should. As a result, a study in the Archives of Disease in Childhood found that children who drank lower-fat milks were actually more likely to be overweight later in life. Ludwig found that while bagels, rice and instant oatmeal may be associated with weight gain, whole milk was not.

In addition, while whole milk’s higher amount of saturated fat may raise bad cholesterol levels, low-fat milk may lead drinkers to eat more foods higher on the glycemic index. In turn, this can increase the level of triglycerides, which can worsen risk factors of heart disease, such as high cholesterol and hypertension.

Finally, some experts suggest flavored low-fat milk just to get kids to drink the stuff, but these can contain more sugar, which can result in packing on more pounds. So while experts still recommend children 9 and older consume three or four cups of dairy products a day, the milk does not have to be low-fat or skim. Some say it should be food for thought for adults as well as they make their dairy choices.

Today’s trivia

The St. Louis Blues have just scored hat tricks in back-to-back games. But who is the only NHL player ever to score hat tricks in three consecutive games — not just once but twice in one season? (And, no, not even the Great Gretzky accomplished that.)

Answer to Wednesday’s trivia: As a scientist, Sweden’s Salomon Andree published journals on air electricity, conduction of heat and inventions. But on July 11, 1897, the daredevil set out to do something even more groundbreaking: He wanted to become the first man to reach the North Pole by using a hydrogen balloon.

Sadly, he died in the attempt. Soon after liftoff, he had lost two of the three sliding ropes that were supposed to act as a rudder by dragging on the ice. Worse, he and his two crewmates quickly found themselves in a rainstorm with high winds. The balloon iced over and eventually was forced down.

They had brought along sledges, a boat and provisions for three months, but the harsh conditions eventually wore them out. After two months of battling shifting and uneven ice, Andree, an engineer and a photographer perished in October on Norwegian islands in the Arctic Ocean. Their bodies, along with Andree’s diary, weren’t recovered until 1930.