Should Milk Be Refrigerated?

Americans traveling abroad often remark upon the presence of unrefrigerated milk in foreign grocery stores. Opaque cardboard cartons -- much like those in which almond milk or chicken broth might be sold here -- are routinely stacked in pyramids right on the floor. Once the customer has opened the carton at home, he or she will refrigerate it, but until the seal on the box is broken, the milk is considered shelf-stable for as long as nine months.

What goes unnoticed by many of us is the fact that we too have unrefrigerated milk in our stores. It's usually a single serving cardboard container that can be punctured at the top with an affixed straw, much like a juice box, but other container sizes and materials occasionally get it on the action as well. You'll probably find the unrefrigerated milk in the cereal aisle, just sitting there on the shelf, as innocuous as anything. What's the deal?

Population Growth and Pasteurization

It all started when a hardworking scientist took a vacation to a popular wine-producing region, only to discover that the local libations were too sour for his liking. He suspected the blame lay with microorganisms, which just so happened to be his area of expertise. After some experimentation, he established a process by which the wine could be briefly heated to a fixed temperature, killing off the microbes without hurting the flavor. If Louis Pasteur hadn't had such a finicky palate, the milk market might look quite different today.

In fact, it was quite a while before it occurred to anyone to try out his wine-preserving method on milk. As industrialization took root throughout the world, however, and the distance between cow and consumer kept getting bigger, milk grew into a major source of disease. Raw milk can contain salmonella, escherichia coli, and listeria, among other harmful pathogens; at one time it was also a very effective conductor of tuberculosis. In this climate pasteurization was like a miracle. It transformed commercially produced and distributed milk into one of the most reliably safe foods available.

Pasteurization of milk has a few levels. Vat pasteurization, the old-school method, involved heating milk to 145 degrees Fahrenheit for 30 minutes. High-temperature, short-time pasteurization (HTST), which is the most commonly used method in the U.S. today, caps out at 161 degrees for 15 seconds. Finally, ultra-high-temperature (UHT) pasteurization, which is the most commonly used method in the rest of the world, skyrockets to 280 degrees for just two seconds.

Following HTST, milk is considered safe from harmful contamination as long as it is constantly refrigerated. Following UHT, even refrigeration is unnecessary until after the package is opened -- as you might imagine, that intense temperature is enough to blow any potential pathogens to smithereens. But an emerging school of thought maintains that even HTST constitutes more processing than milk needs.

Flavor and Nutrition

At the opposite end of the spectrum from cardboard-carton milk, you'll find the pale yellow, creamy and reportedly delicious dairy product that is raw milk. Consumption of raw milk, usually purchased directly from small dairy farmers, has become increasingly popular in the past two decades. Proponents claim that it is easier to tolerate than pasteurized milk, that it strengthens teeth and bones, and that it is protective against childhood asthma and allergies. Some even claim that it has reversed the progress of cancers.

The relative safety of the two, however, is a bit of an open question.

Proponents of raw milk say that with modern standards of hygiene applied, dairy isn't dangerous; they also believe that there are antimicrobial substances in raw milk that keep it naturally safe through as-yet-unidentified mechanisms. Opponents point out that between 1993 and 2006 the U.S. saw 4,413 documented cases of disease outbreak related to consumption of nonpasteurized products, resulting in 239 hospitalizations and three deaths. They also point out that kids bear the brunt of the impact of contaminated foods. Sixty percent of these cases involved people under the age of twenty.

In the absence of a long-term population study that would prove or disprove any of this in a statistically significant manner, one might conclude that the U.S., for once, is doing food policy better than the rest of the world. The HTST process has been shown repeatedly to keep milk safe and to maintain the bulk of its nutritional value. Taste-wise, it avoids the Maillard browning that UHT milk is said to experience, keeping it closer to the original flavor. In short, HTST milk sounds like a nice compromise between poles.

Environmental Impact

But, as you might have expected, nothing's that simple. Those refrigerated cases that keep HTST milk nice and cold have quite the environmental impact, and here in the U.S. we have a lot of 'em. Your local 7-11 probably has a bigger selection of HTST milk than most grocery stores in other countries. In fact, UHT milk only became as popular as it is in other parts of the world because, for reasons of cost or virtue or both, many countries are more energy-conscious than we are.

As environmental concerns continue to mount, it has been suggested that transitioning to only UHT milk would be an effective way of reducing emissions of the fluorinated gases that are byproducts of refrigeration, as well as the greenhouse gases necessary to power all those cold cases. (While raw milk is theoretically produced, sold, and consumed in a manner that circumvents these problems, one could be forgiven for wondering whether its boutique model could really be expanded to reach the majority of consumers. Even if it is one day proven to be as safe as pasteurized milk, it was the mass distribution of dairy products that created the problem with raw milk in the first place.)

So, should milk be refrigerated? It's a simple question with a complex answer that depends on your beliefs, your priorities and your palate. But then, what about the world of food isn't complicated?