When it comes to cooking oils, some of which I also use in salad dressings in combination with aromatic nut and olive oils, many people decide on those with the highest smoke points, the temperature at which a cooking fat begins to break down and deteriorate. The fats break down and generate free radicals, which can have health implications, especially in our oxidative environment.
Oils that have broken down significantly are referred to as rancid. Rancidity usually produces an odor, that is not a good sign for the oil. If you do a lot of high-heat stir-frying, you should look for an oil with a high smoke point. Those that I would recommend are safflower oil refined (490 °F ), coconut oil (450 °F), and grapeseed oil (420°F).
Storing all your oils appropriately and screening for rancidity before use is important. For example, olive oil should have no aroma. I used to use olive oil for cooking, but now that I know of its low smoking point, I reserve for baking or dressings. For years I had associated a smell with olive oil. It was the rancidity that I smelled and now my nose is keen to the odor. I have found it is not unusual to open a new bottle of olive oil and smell rancidity, so select your brands well. Also, oils should be kept in cupboards (not near the stove top where it’s frequently warm) and in dark bottles to protect from oxidation due to light. Also, free radicals propagate over time so sniff your oils before use.
Note: The picture was chosen for artistic purposes only and is not my picture of oil. The bottle is not dark so does not meet my standard.