Why do my stored cashews smell like fish? I have a 30 Oz plastic jar of Roasted, Unsalted Archer Farms Cashew Nuts. I've noticed that after having it 'open' for a week or two (i.e. the lid is tightly screwed onto the jar, but the initial paper seal has been broken), the nuts begin to develop a fish-like smell. They are still hard and there is no sign of mold --- the nuts are perfectly good, but they don't taste quite like typical cashews.

First, what's going on here? I read somewhere that this is due to oxidation, perhaps a too-high moisture level in the air when I open the jar. Second, how can I correct this? Would it be better if I were to keep the cashews in the freezer? Should I buy salted cashews instead? Intuition tells me that salted cashews should not be affected by this issue, as the salt would absorb the moisture.
I believe the fat in your cashews is becoming rancid. That would most likely be caused by oxidation. Exposure to air is the chief culprit. However, exposure to light or heat could also accelerate this.

I'd wager you got a jar of nuts that wasn't quite sealed. Have you had this problem before with other jars of these nuts? 1-2 weeks is an abnormally short period of time for this problem to occur in a sealed container.

It's also possible that the nuts are old. Have you checked the "best by" date?

Freezing does not stop oxidation. It would ensure a relatively cool and dark storage place for them, though.

The only way to stop oxidation is to prevent air from touching the food.

Equipped with a new jar with a tight seal and a cool, dark storage place... I think you'll do just fine in subsequent cashew ventures.