While the term "shortening" can refer to any type of fat used to add a soft, cake-like or flaky texture to baked goods, it most commonly refers to vegetable shortening. Vegetable shortening is made from vegetable oils, which are processed to produce a fat that remains solid at room temperature. It's also notable for a very long shelf life, though it will eventually spoil.
Vegetable oil shortening has a longer shelf life than most other fats, but will become rancid after a year or two.
Vegetable shortening is made from plant oils, which are liquids. When these oils are hydrogenated, they go through a chemical process that changes their polyunsaturated fatty acids to saturated fatty acids, according to the King Arthur Flour website. Hydrogenation changes the consistency of the vegetable oils to that of a solid, with a texture similar to lard or butter, while increasing their shelf life. Unlike butter or margarine, you can leave vegetable shortening at room temperature without worrying about spoilage. While you can also leave out hydrogenated lard, vegetable shortening has about twice the shelf-life of the animal fat. Like any vegetable oil, though, it will turn rancid eventually.
How Long is it Good?
If you haven't opened your can of vegetable shortening, it may last up to two years in your pantry from the time of purchase. When you open the can, it will likely last for up to one year before spoiling. In stick form, it lasts for two years unopened, but only six months if opened. Refrigeration isn't necessary for your shortening, which can safely stay at room temperature, although refrigeration may prevent the shortening from melting in very warm climates. Allow cold shortening to return to room temperature before use because it can become hard and less malleable in the fridge.
Checking for Rancidity
Most manufacturers of vegetable shortening list a "best by" date on the package. This date is determined by the manufacturer, and the shortening will usually be at its best until this time. After the expiration date, though, your vegetable shortening may still be good. Check the shortening by visually inspecting, smelling and tasting it. Usable shortening should appear white in color and have a neutral odor and taste. If your shortening has a strange, rancid odor or taste, has become darker in color or its texture has changed, discard it because it has gone bad. While it's not likely that using spoiled shortening will make you sick, it can ruin any baked goods you use it in, giving them an unpleasant taste.
If your vegetable shortening has spoiled, you can substitute lard, butter or margarine for it in your recipes. Substitute the same amount of butter or margarine for shortening; when using lard, use two tablespoons less per cup in your recipes. The shelf life of goods prepared with shortening is usually determined by the other ingredients in them. For example, frosting prepared with shortening and sugar alone may last for up to six months in the pantry, but if it includes butter, it will only last one to two days.