Expired protein powder: Do you scoop or toss?

Protein powders don’t spoil the way meat or dairy does, because a dry environment makes it nearly impossible for microbes to grow, says Bob Roberts, Ph.D., a professor of food science at Penn State University.

So unless you’re storing your canisters in a warm, humid place (like the bathroom or your gym locker), you’re fine on that front.

As for the muscle-building mojo of protein powder, it does diminish after the use-by date has passed. You can blame a chemical reaction called Maillard browning: The protein reacts with sugar left over from when the whey was extracted from milk, resulting in a gradual breakdown of the amino acid lysine.

“If you lose lysine, then the powder will not be as complete of a protein,” says Roberts.

Only a day or two past the expiration date? Put a bit of it on your tongue. Another telltale sign of Maillard browning is a fade in flavor, says Roberts. If you taste cardboard, toss it.

And if it always tasted like cardboard, then no wonder the stuff sat around for so long