Follower Christy sent another great question, “Which oils/fats need to be refrigerated and which do not. Also, shelf life. I'm always looking at that little bottle of sesame oil and wondering…”
Heres another topic that simply doesn't get the attention it should, from both a food quality and food safety perspective, so let's have a look.
Air, heat, light, and age all can and will negatively impact the quality of most edible oils. High storage temperature and oxygen exposure are the primary causes of spoiled oil. Rancidity will result rather quickly if not properly stored. The same compounds that provide the smells and flavors we like in a given oil will cause unpleasant changes if we're not careful. That means, naturally, you should store your oils in a cool, dark, dry place, and in an airtight container. As such, cruets or open top pour spouts are not the best choice, even in a busy home kitchen. Additionally, exposure to direct sunlight causes a substantial loss of antioxidants, especially tocopherols, meaning many of the benefits of healthy oil choices are lost as well.
Rancid oil generally won't do you serious harm; nonetheless, it's obviously not a desirable pantry guest. When your oil looks, smells, or tastes off, it is, and should be discarded. Smells described as winey, metallic, or skunky are clear signs that something is amiss.
As for shelf life, the method of production for the oil in question has a bearing. Most unrefined oils, (cold or expeller pressed), will keep for 3 to 6 months, properly stored. They may be refrigerated, and will last a bit longer as a result, though they'll tend to solidify and will need to return to room temperature to liquefy again. Too many such cycles can impact the chemistry of the oil, and the need to re-liquefy might inhibit spontaneity, so you're probably best served buying smaller quantities and storing carefully at room temperature. If that sesame oil Christy mentioned is older than 6 months, it's time for it to go. Refined oils, (oils obtained from heat and solvent extraction), tend to keep twice as long as unrefined oils; at least 6 to 12 months if stored properly. Oils high in polyunsaturated fat, (walnut, safflower, and hazelnut oil, for instance), have a much shorter shelf life than high monounsaturated, (think peanut), or saturated fat oils, (like canola). Again, refrigerated storage is an option, but small containers of fresh oil at room temp is best.
Most solid fats traditionally used in cooking are animal based, (lard, ghee, duck fat, schmaltz, etc), however tropical plant oils such as coconut oil, (one of my favorites), are also solid or semisolid at room temperature, as are vegetable shortening and margarine, (made from plant oils and solid due to the hydrogenation process). Many solid fats also contain a higher proportion of saturated fat than liquid fats do; as such they're generally quite stable and will keep well for at least 6 months. Solid fats will absorb the flavor or scent of other foods readily, so should be kept in airtight containers.
Our industrial food system has lead us all, to some degree, toward keeping things longer than we should. Just because something can last 6 months doesn't necessarily mean that we really want to cook with it. I'll guarantee that, whether the ingredient be oil, fat, spice, or even flour, fresh will always taste better than many moons old.