There’s nothing inherently wrong with Costco’s milk, but there is one practical reason some shoppers say to think twice before putting it in the cart: you may simply be buying more than your household can finish. Costco is built around bulk shopping, and several of its milk options are sold in multipacks. For example, Kirkland’s ultra-filtered 2% milk currently comes as three half-gallon cartons—1.5 gallons total.

That can be a great deal for a large family or anyone who goes through milk quickly. But for one or two people, buying a large quantity of fresh dairy can backfire if some of it spoils before it gets used. Costco itself recommends planning storage space carefully when buying groceries in bulk and notes that many bulk foods may need to be divided or frozen to avoid waste.

The other thing to check is your refrigerator space and the date on the package. Milk needs consistent refrigeration, and Costco specifically lists its refrigerated Kirkland milk as a product that must be kept cold. If your refrigerator is already packed, buying several large cartons may not be as convenient as grabbing one smaller container from a regular grocery store.

So the warning isn’t that Costco milk is poor quality or unsafe. In fact, bulk pricing can be excellent if you actually use what you buy. The real question is whether the savings still make sense after considering how much milk your household drinks.

Sometimes the cheapest milk per ounce becomes the most expensive option if half of it ends up going down the drain.