The One Thing You Probably Didn't Know About Milk From Costco

Have you ever felt that milk from Costco tends to last just a little bit longer than milk bought elsewhere? Some customers of the wholesale club certainly seem to think so. One took to Reddit to say that their Costco milk seemed to last a week past its expiration date even while opened, and multiple other customers responded saying they've had similar experiences. There's yet to be a scientific study on just how long Costco milk — that is, Kirkland Signature brand milk — will last in the average fridge, but evidence suggests Costco is not the worst place to buy milk. Far from it. As it turns out, the popular wholesale retailer has its own standards in place, complete with bacterial tests that may just help prolong the life of its milk.

While all Grade A milk in the U.S. has to meet specific quality standards as per the FDA (though it's worth noting the FDA suspended its milk quality inspections due to workforce cuts in 2025), Costco doesn't settle for the basic standards. The Kirkland, Washington-based company runs its own microbial tests — 60, to be exact — before any batch of milk ships out. Plus, according to the company's Food Safety & Quality Audit Expectations rulebook, any Kirkland label milk suppliers (not including Costco dairy alternatives like soy or oat milk) have to pass surprise inspections at least once a year — twice if they're in China. These checks cover everything from the farm to the processing plant, leaving as little room as possible for issues.

As the company explains in its quality expectations booklet of 2023 (which, in case you're wondering, remained largely the same as the last update a few years prior), dairy supplier audits are both mandatory and can be conducted at any time. If a dairy facility scores under 85% during an inspection by Costco's auditors, it has to then get re-inspected within 60 days. Fail that audit? Costco will send its inspectors back and have the supplier pick up the tab. On top of that, inspectors are rotated out to prevent bias.

And that's not all. If any batch of milk fails even just one of its required microbial tests, it doesn't get shipped out. Costco also has stipulations for supplier workers regarding food handling and cleanliness, and it also requires any facility with dairy cattle to undergo "an animal welfare or certification audit." This is in addition to the regular milk testing and facility inspections. And if all of that doesn't already sound like quite the list of standards, Costco also requires all water that is used in its products be tested annually for E. coli and any microbial pathogens found to be of concern in the area the facility is in. Of course, none of this guarantees Costco products are totally free from issues (like the biggest Costco scandals of all time) — it just means that, as far as Kirkland milk goes, you can rest assured it's gone through heavy scrutiny before reaching your hands.