• iStock

  • iStock

  • iStock

  • iStock

  • iStock

There's so much more to a gallon these days. Ultra-pasteurized, rBST-free, omega-3 fortified... and we're just talking milk from cows.

We asked Jane Andrews, manager of nutrition and product labeling for Wegmans, to help us sort through the cartons in the dairy aisle. The supermarket chain moves a lot of milk, much of it a house brand produced by a cooperative of family farms in upstate New York and Pennsylvania.

  • 1. How to buy milk.

    iStock

    Milk in opaque containers is more ideal than glass, as exposure to light will break down some of the vitamins in milk, Andrews said.

    Choose the carton with the latest "use by" or "best by" date stamped on it, but don't feel bound by that date. It indicates peak freshness, but not necessarily the starting point for spoilage.

    That said, don't buy more milk than you need, and keep the milk cold. No matter what the date on the carton reads, once opened, it'll last about a week in your fridge, Andrews said.

  • 2. What Happens to Milk Before You Buy.

    iStock

    Most milk sold in stores is pasteurized and homogenized.

    Homogenization is a mechanical process that breaks down fat molecules so the milk stays, well, milky smooth. Non-homogenized milk separates into layers. You’ll see it labeled as "cream top," or something similar.

    In pasteurization, milk is quickly heated and then cooled to kill harmful bacteria such as E. coli and salmonella. Ultra-pasteurization takes that up a notch to a much higher temperature, resulting in an even longer shelf life, up to six months for an unopened, shelf-stable carton, Andrews said. Some say ultra-pasteurized milk tastes a bit different, "more cooked," she said.

  • 3. What's the Deal With Raw Milk?

    iStock

    Raw milk is not pasteurized—and highly controversial. Advocates say it's more nutritious. The USDA, FDA and CDC say it can carry potentially deadly bacteria.

    Depending on where you live, raw milk might be hard to find. It's limited to on-the-farm sales in some states, and is illegal to sell in 19 states.

  • 4. Where's the fat?

    iStock

    Whole milk is 87 percent water and 13 percent other stuff: fat, protein, carbohydrates, vitamins and minerals. High-speed centrifuges spin off the fat to produce lower fat varieties: reduced fat (2 percent milkfat), lowfat (1 percent milkfat) and skim (nonfat).

  • 5. The Real Deal With Organic Milk

    iStock

    Organic milk, as defined by the USDA, is from cows raised on organic, pesticide-free feed, without growth hormones or antibiotics. Federal rules also require that the cows spend at least four months on grass and that 30 percent of their diet is from grazing on pasture.

    Speaking of omega-3s, some research suggests organic milk has more of them than conventional milk. Still, if it's omega-3s you're after, you're better off eating fish, Andrews said.

    "Don't go with organic or grass-fed because you think you're going to get more omega-3s. It's inconsequential. Go for it because you believe in [organic food], or you like the taste," she said.

    Whatever your reasons, you'll pay a premium for organic — $1.86 more on average for a half-gallon, according to the USDA.

    Check out more must-know milk facts before you head to the dairy aisle.

    More from Epicurious

    20 Must-Try Ways to Pair Items You Already Have In Your Pantry

    The 57 Best Cooking Tips of All Time

    12 Lightning-Fast Chicken Dinners to Make Now

    This Recipe For Boiling Water Has 908 Comments