Sometimes, when I'm eating walnuts, I'll find one with some dark spots on the kern surface, as shown in the photograph below. I normally prefer to err on the side of caution (I think I read somewhere once about them being some sort of mold) and throw it away. Just in case I'm throwing away some fine and expensive delicious walnuts, I'd like to ask if somebody know what these spots are, and if they are safe to eat or not.
Thaks for your time, and sorry if it's a silly question.
I don't see anything there that looks problematic, but it's hard to know for certain from the photo. Generally, mold will have a textural difference (matte and/or fuzzy rather than glossy). If you wipe it with your finger some will smear and come off. Oxidation can change the color (but usually does not), and all nuts will oxidize over time. Eating rancid nuts is not ideal in terms of taste and health, but a little oxidation isn't going to hurt you, and all fats will have some oxidation. Keeping your nuts well-sealed in dry, cool storage away from light will considerably slow oxidation. Other causes for discoloration could be bruises, insect damage, natural variations in pigment, and fungal infections.
If you are buying your nuts from a reputable store (not one that sells stock that's past its best-by date), nuts are very safe, so I wouldn't worry too much. If the bag is torn or otherwise damaged or if there's any indication of humidity in the bag, then I'd return them to the store.
