HTST pasteurization vs. UHT pasteurization
According to the International Dairy Foods Association, pasteurization is a process that applies heat to destroy pathogens in foods (similarly to the way white blood cells destroy pathogens like bacteria and viruses in your body). For refrigerated dairy products, high-temperature short-time (HTST) pasteurization involves heating every particle of milk or milk product to at least 161°F using metal plates and hot water. The milk remains at high heat for at least 15 seconds, followed by rapid cooling. It then has a shelf life of five to 15 days.
Ultra-high-temperature (UHT) pasteurization, also known as aseptic processing, involves heating milk using sterile equipment and filling it under "aseptic conditions." Voilà! Once you swim through all that jargon, you're presented with milk that will help you survive should we ever find ourselves invaded by aliens and forbidden from going to Whole Foods (we've all seen Signs—not pretty).
Back to the whole "aseptic" thing. All aseptic operations are required to file their processes with the Food and Drug Administration. Therefore, there is no set time or temperature for aseptic processing. The FDA's "Process Authority" establishes and validates the proper time and temperature based on the equipment used and the product being processed. Basically, this milk is watched more closely than any child you ever babysat.
"Dairy products that have been heat-sterilized and wrapped in sterile packaging do not require refrigeration as the sterilization prevents the milk from spoiling," says Lisa Moskovitz, RD, CDN, founder of NY Nutrition Group.
Nondairy milk products are processed the same way. Blue Diamond Almond Breeze processes its refrigerated almond milk products using standard dairy processing (HTST) and produces their shelf-stable products using UHT processing. The shelf-stable stuff comes in aseptic carton packaging that, according to Blue Diamond, is "designed for shelf stability of the unopened product for an extended period." Silk says the same of their soy milk, almond milk, coconut milk, and cashew milk. Still, all brands suggest refrigerating shelf-stable milk before drinking it. (Warm milk is for cats.) And always refrigerate shelf-stable dairy and nondairy milks after opening the package.
Is one more nutritious than the other?
Apparently, all is fair in love and shelf-stable milk. "While heating [shelf-stable milk] to high temperatures through the sterilization process can deplete some nutrients, it doesn't affect key nutrients such as protein or calcium, and is usually fortified back with many nutrients that it may have lost, including vitamins A and D," says Moskovitz. But wait—aren't "fortified" products typically a no-no? "In this case, since the nutrients are just being added back, and not necessarily in excess of what the milk had to begin with, these fortified shelf-stable dairy products should not pose any harm. All in all, both versions are nutritionally equivalent."
Do they taste different?
While the taste may vary slightly due to the heating process, Moskovitz claims that "when you finally open up the carton, it is room temperature versus cold, refrigerated milk." So have some patience and place your shelf-stable milk in the refrigerator for an hour or so before you drink it.
Now you can return to your office kitchen and snag yourself a nice (probably Keurig-created) cup of joe without wrinkling your nose at the "creepy" boxed milk options in front of you. It's only weird if you make it weird, guys.