Will oil smell horrible if it's gone rancid?

I have a really old (more than two years, we’re talking) bottle of sesame oil. I have used it on occasion, but not often.

Every now and then I wonder if it’s gone rancid, and I open it up and sniff it. It usually just smells like toasted sesame seeds. I usually presume this means it’s fine, and proceed with using it. But I would prefer not to ruin something with rancid oil if it’s likely to taste bad but not smell bad.

Does anyone know? And, as is probably obvious from this post and just about any other cooking post I’ve made, I’m not the greatest cook. Which explains why I have a bottle of sesame oil that’s years old and been through a few moves with me.

Sesame is one of those oils that doesn’t seem to spoil. It does lose its favor though.

I’m pretty sure generic Vegetable Oil (i.e a mixture of corn and/or canola) goes somewhat rancid after less than two years, but I’ve cooked with it (i.e a more than two year old bottle of oil) accidentally and while it smelled off it didn’t smell that off. It smelled sort of like a pleasant fart. After only experiencing mild diarrhea I of course counted myself lucky and threw out the bottle of oil that I had only read the expiry date of after I had cooked with it, but then ate the results of anyway on the principle that oil can last for years.

After all, it didnt smell that off. But why take the chance that my intestinal reaction was due to the chicken and not the oil, yanno?

Huh, interesting. It still smells pretty potent.

ETA: That’s a fair point, Ludovic, but this doesn’t smell off at all.

On the contrary, assuming you’re talking about the dark sesame oil - that stuff seems to go off rapidly compared to others. Whenever I see oil rancidity being discussed, the near-immediate advice is to keep the dark sesame in the fridge, where it will stay good for a really long time. Dunno about light sesame though.

If you’re worried, refrigerate any oil you don’t go through quickly. And a tiny taste should dispel any questions about whether something is rancid.

Huh.

Well, I think this is dark, and it definitely hasn’t been refrigerated. However, it doesn’t smell off, just “toasted”. Maybe that is off.

I’ll taste it tomorrow. Now is bedtime.