The shelf life of protein powder is given on the packaging as a best-before date and depends heavily on correct storage. Unopened and stored dry, powder generally stays stable for a longer period, while after opening the recommended period of use is usually shortened considerably. A clearly changed smell or clumped powder can be signs that the product is no longer at its best.
What matters most for shelf life after opening is protection from moisture, as protein powder can absorb water from the air and then clumps or becomes more prone to changes in quality. Dry, cool storage away from light, ideally tightly sealed, extends the period of use. A wet spoon in the powder should be avoided. Smaller containers help to use up a powder within the recommended time after opening.
Notes on reading manufacturer information are provided by the guide Reading the ingredient list of protein powder, and more on the powder itself is explained in the entry Protein powder.
