Regular sesame oil, generally, is a darker, bit more deep golden color than say, corn or peanut oil. Toasted sesame oil is much darker, golden brown to brown. Its flavor is as Nicole descibes. Either oil--any, actually--will become rancid when exposed to air; how long that will take depends on several factors. Toasted oil has a shorter shelf life. It's best used fresh, in dressings, (again, like Nicole mentions), not cooked with. Bob: It sounds like you have toasted. A lot of people can't stand toasted oil, even if fresh, so it's hard to say if yours is rancid or just something you don't have a taste for.