Why Some Costco Customers Are Returning This Popular Snack

Walnuts: versatile, nutritious, and yummy to boot. When walnuts are fresh, they're a crunchy, savory delight that fuels your body and satisfies your cravings. When walnuts have gone rancid, however, few things are more disagreeable. Unfortunately, rancid walnuts are a complaint that seems to be part of the mix when it comes to Kirkland Signature walnut halves at Costco. While our favorite Costco finds are a treat for both our bellies and our wallets, like frozen Hokkaido scallops that customers love or frozen Kirkland french fries with great reviews, certain items are a swing and a miss ... and, per some social media buzz, the store-brand walnut halves at Costco might be worth some measured consideration.

"Kirkland Walnuts are consistently rancid," starts a complaint on Reddit, in which the writer goes on to note, "Basically, our family had been settling for semi-rancid walnuts for the past 2 years, thinking that this is as good as it gets." Elsewhere on Reddit, gripes about Costco walnut quality flowed freely: "I also recently returned a packet of Kirkland Walnuts, they just tasted off," one commenter reported. "[T]oo expensive for rancid walnuts. [H]ow disappointing," another summed up. 

The reported rancidity of the walnuts is adding insult to injury, as Redditors have complained about dramatic price hikes on this same product in 2025. However, it's interesting to note that the controversial packages of walnuts enjoy a 4.8 out of 5-star rating on Costco's website, and tons of reviews seem pleased with them. Peppered through the happy reviews, however, are multiple complaints about rancid batches, which seem to be more frequent of late than in the past.

It's worth noting that walnuts go rancid quickly, much faster than other nuts. That's because walnuts are fatty, and when the fats in walnuts are exposed to warm temperatures, they break down and display the nasty taste and bitter smell that characterize rancidity. We've mentioned that the best way to store nuts is in the freezer, and this is especially true for walnuts — in other words, you really want to keep them cool. If you'll be eating them in the near future, stashing them in the fridge is probably good enough. If you buy a big bag (like the Costco Kirkland Signature three-pounder, for example), you may want to freeze any excess product until it's ready for consumption.

Walnuts' sensitivity to warmth leads us to wonder if improper storage is behind the smattering of customer complaints. There's probably no way to prove it, of course, but if the retailer is stashing the bags in places above room temperature — which might occur during transport, even — the walnuts would, conceivably, have the opportunity to go rancid before they are even opened. It's worth noting that Costco sells the bags out on the main floor and not in the refrigerated section.

Does this mean that you should always steer clear of Costco's walnuts? We'd say to proceed with caution. One of the best parts of shopping at Costco is the reassurance of its renowned Risk-Free 100% Satisfaction Guarantee, which backs every item sold at the warehouse. If your walnuts or any other Costco item are not to your satisfaction, take comfort in knowing that you can just about always obtain a full refund.