Please could you tell me if I can use margarine as a substitute for vegetable shortening?
Vegetable shortening (such as Trex, Cookeen, Crisco and Copha) is vegetable oil that has been hydrogenated, a process which means that the oil becomes solid at room temperature. Vegetable shortening is 100% fat and fairly flavourless. Margarine is also made from hydrogenated vegetable oil but also contains water plus milk solids and/or flavourings. Margarine is typically 80% fat and will usually have a slightly buttery flavour.
You can in some cases substitute margarine for vegetable shortening but it depends on the recipe. For frying it is not a good idea to substitute margarine as usually the temperature for frying is high and the milk solids in margarine will burn and affect the taste of the food you are frying. In cakes you can usually use margarine instead of shortening. For cookies and pastry you can also use margarine instead of shortening but the texture of the finished article may be affected. Using shortening will give a flaky, slightly crisp texture. However the water in margarine will affect the gluten in flour so if you use margarine instead of shortening in cookies and pastry then they may be slightly tougher and harder than the versions made with shortening.