Does Protein Powder Go Bad?

Expert Verified By: Trevor Kashey, PhD

Because it doesn’t rot, melt, or decompose like your standard refrigerated protein and produce, some of us tend to think of protein powder like flour, sugar, and other pantry staples — the kind that you forget to throw out after they expire. But when you remember that whey comes from milk, you might realize that it could be kind of important to pay attention the expiration date.

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Does Whey Protein Expire?

Sure, it has an expiration date right there on the tub. You did check for an expiration date, right? Because as great as that ten-pound bag of Gold Standard Whey sounds, if you don’t finish it in a couple of years then you’ll likely hit that expiration date.

Does that matter?

Here is where we should say this isn’t medial advice and we would never recommend consuming expired food. When it comes to whey, a lot of the reason it has an expiration date has to do with moisture getting into the bag or tub, which is how you can get mold or other troublesome organisms.

It’s a pretty dry product to begin with, obviously, so the risk isn’t crazy high but with repeated openings throughout the months and years, the occasional use of a wet scoop, a splash of milk falling in as you hastily shake your shaker… look, stuff happens.

If the whey has changed consistency — like if it’s more densely packed and closer to wet sand than when you bought it — that might be a bad sign. If it smells weird or looks moldy, that’s a bad sign.

whey protein

If the flavor starts to diminish or you start to see browning, that can be a sign of the “Maillard Reaction,” where the protein reacts with sugar in the product that gradually breaks down the amino acid lysine. Yep, it can indeed happen in old whey, according to a 2005 study published in the Journal of Dairy Science.(1)

If you lose the lysine it really just means the protein might be less complete, which probably isn’t as big a deal as you think so long as all the branched chain amino acids are still there to help with muscle protein synthesis, according to research published in The Journal of Physiology.(2)(3) It’s also worth remembering that whey is so low in sugar that it’s unlikely to affect all that much of the lysine. Still, you might not want to consume something that’s so old it’s digesting itself.

[Is grass-fed whey actually healthier? Check out our in-depth article.]

lots of whey protein

Does Whey Protein Denature?

One thing a lot of people worry about whether or not their whey has been made or stored or aged in such a way that it’s denatured. If you look at a lot of different whey protein powders it’s likely you’ve seen plenty swearing that they’re cold processed or processed without acid to make sure nothing has been denatured.

“Protein denaturation has no practical impact,” says Ohio-based biochemist Dr. Trevor Kashey. “Ironically enough, if protein isn’t denatured then it’s not digested, and then not absorbed. Protein has to be denatured to be nutritive. Amino acid supplements are literally as “denatured” as you get!”

He adds that protein powder probably denatures as it ages but this doesn’t mean much practically.

“Whey is a waste product of making cheese, right?” says Kashey. “In most cases, cheese is made by acidifying milk so the casein comes out. So even the process of making cheese denatures the whey and purifying the whey denatures it more.”

People get held up on “denaturing” whey, but it’s not something that should be a big concern.


The Takeaway

Expiration dates are just an estimate and unless you find the whey has started to taste like cardboard or grown mold or started to smell, it doesn’t seem likely that it will no longer be safe to consume to build muscle. We still wouldn’t recommend eating expired food, but we’d be lying if we said we throw out our whey because it’s a little past the expiration date. Use your head and give it a thorough examination.

Then start putting aside money for a new tub.


  1. Sithole R, et al. Rate of maillard browning in sweet whey powder. J Dairy Sci. 2005 May;88(5):1636-45.
  2. Breen L, et al. Leucine: a nutrient ‘trigger’ for muscle anabolism, but what more? J Physiol. 2012 May 1;590(9):2065-6.
  3. Norton LE, et al. Leucine content of dietary proteins is a determinant of postprandial skeletal muscle protein synthesis in adult rats. Nutr Metab (Lond). 2012 Jul 20;9(1):67.