What Is Shelf-Stable Milk And Why Doesn't It Need To Be Refrigerated?

Though my older child is entering first grade this year, I've been packing her lunches for years. As other working parents can attest, many of us start packing lunch before our children can even chew. And then, depending on what school lunch is available, and whether our kids will eat it, we continue to pack lunches. Every. Single. Day.

I've always looked for ways to make these meals nutritious and filling but also easy, because I am tired. So tired. One of the ways I did that was to include shelf-stable boxes of milk, which I found in the inner aisles of my grocery store, not the cooler. But what is shelf-stable milk, exactly? How does it differ from the little cartons of cold milk served at many schools?

Shelf-stable milk, also known as "aseptic milk," is indeed normal milk. Most of the shelf-stable milk brands available at my grocery store tend to be organic, but it is normal old organic milk. 

The stuff we get in the cooler and the milk we find on the shelf just differ in how they're pasteurized.

Whereas the milk we get from the cooler is pasteurized at around 160 degrees Fahrenheit for approximately 15 seconds, ultra high temperature (UHT) pasteurization is "hot and fast," as Bon Appetit puts it. In UHT pasteurization, milk is heated to between 270 and 280 degrees Fahrenheit for just two seconds before being quickly chilled.

"This hot and fast approach kills nearly all bacteria in milk and is referred to as UHT (ultra high temperature, or aseptic) pasteurization," explains Bon Appetit. "It's this one-two punch of bacteria-killing UHT pasteurization and aseptic packaging that makes shelf stable milk so long-lasting."

Obviously, a big difference between shelf-stable milk and regular milk is how long they last and where they should be stored. Depending on the brand, unopened shelf-stable milk can be good for up to nine months. Once opened, however, it should be consumed within a week. While unopened aseptic milk can be stored in a pantry or on a kitchen shelf, opened containers should be refrigerated.

Unopened regular milk, on the other hand, should be consumed in a week and needs to be refrigerated. Regular milk that's been opened is good for about three days.

Some say shelf-stable milk tastes identical to refrigerated milk, while others say it has a sweeter taste. In an explainer on its website, Organic Valley, one of the brands I can get at my grocery store, says the two products taste the same: "Yes! Shelf-stable milk tastes just like refrigerated ultra-pasteurized milk. Although you can drink it at room temperature, we recommend drinking it cold. Simply pop a few into the fridge every day or two and you'll always have some ready for little hands to grab or for a post-workout recovery."

A report by the School Nutrition Association found that shelf-stable milk can have a slightly sweeter flavor than milk that's undergone traditional pasteurization, but it's not necessarily a bad thing. This flavor profile is often covered up by vanilla or chocolate flavor additives, anyway.

"There is a slight difference," says the School Nutrition Association's report. "However, most people will not notice it, especially in flavored milk. We have conducted several studies in school districts across the country that show conversion was not an issue. In fact, students drank more of the milk in shelf stable cartons and sales increased."

It is in some places! It's common to find shelf-stable milk in Europe. According to The New Republic, leaders have pushed to make shelf-stable milk the norm in Europe: in 2007, the UK's Department for Environment, Food and Rural Affairs (DEFRA) proposed that by 2020, 90% of milk sold should not require refrigeration.

In the U.S., what's holding us back might be tradition. "Americans are used to getting fresh milk from a cow and consuming it within a week," said Bruce Krupke, Executive Vice President at Northeast Dairy Foods Association, in a quote shared by The New Republic. "That's the tradition. That's what Americans have been brought up on. Why would someone who can get fresh milk want to buy a shelf-stable product?"

Nutritionally speaking, there are no added nutritional benefits to drinking shelf-stable milk, and in fact, according to Bon Appetit, "because shelf-stable milks have been heated to a higher temperature, they've lost some of the good bacteria and protein found in refrigerated milk. To compensate, many vendors will add vitamins (like vitamin D or A) or stabilizers." That compensation means you don't lose out on anything by drinking the room-temp cartons, but its benefits over traditional milk are convenience-related, not nutritional.

There could be global benefits, though, and much of the conversation around shelf-stable milk focuses on the environment. Shelf-stable milk is packaged differently than the cold stuff, the latter of which which is primarily in plastic cartons. Shelf-stable milk is packaged using Tetra Pak cartons, which have a cardboard base and are recyclable. Horizon claims many of its Tetra Pak containers get a "second life" as paper products or building materials.

Moreover, since refrigeration isn't required, neither are refrigerated trucks to transport the milk or refrigeration units to store them in store.

All things considered, I'm going to keep buying these milk boxes for my kids' lunches, especially for the little one who is still in childcare and is therefore not at a school where chilled milk boxes are available. It's good for her, it's good for tired, lunch-packing me, and it might ultimately be good for the planet.