Hydrogenation is the process that transforms pure vegetable oil into vegetable shortening using the liquid fats extracted from products such as soybeans or palm kernels. The process rearranges the molecules to produce a fat that remains solid at room temperature, such as vegetable shortening, a white flavorless substance. While shortening can be used in place of other solid fats like butter, margarine or lard, it is more evenly distributed in dough and batter, where it slows down the gluten development in the flour.
According to King Arthur Flour, vegetable shortening is made by a chemical process that changes some of the polyunsaturated fats in vegetable oil into saturated fats. Not only does this extend the shortening's shelf life, but it also makes it more workable for some baking methods, such as creaming and whipping, which cannot be done with oil. Vegetable shortening also lends more stability to cake frosting, but it provides less flavor than butter.
Vegetable shortening is widely used for making piecrusts. The product creates a barrier between the flour and water; as the pie bakes, steam is produced between the layers as the shortening melts, giving the crust a flaky tenderness. Because it is 100 percent fat, shortening also helps cookies retain their shape during baking.