An unopened, properly stored package of dried nonfat milk lasts three to five years. Powdered whole milk, reduced-fat milk and buttermilk, however, aren't suitable for long-term storage because of their fat content. Even under optimal conditions, the taste of the milk may begin to change after a few years. Under the right storage conditions, even if the taste changes, the dried milk remains nutritious and safe for consumption.
Buy, reconstitute and sample a few brands of dried nonfat milk. Confirm that you like a particular product before stocking up, because quality varies widely.
Opt for powdered milk labeled "extra-grade" for the highest quality. Extra-grade products are most easily reconstituted and contain the least amount of scorched particles. They also contain the least moisture and lowest bacteria count, which makes them best suited to long-term storage.
Purchase powdered nonfat milk that's packaged in a vacuum-sealed, airtight, moisture-proof mylar bag. The packaging should shield the product from light. Refrain from opening the package.
Store the dried milk in a cool, dry place. If the product is protected from oxygen, moisture and light, and stored at a temperature around 70 degrees Fahrenheit, you can expect the milk to last about four years. Storage at 50 F preserves the flavor much better. Refrigerate the powdered milk for the best results.