Hydrogenation is widely applied to the processing of cooking oils and fats. Complete hydrogenation converts unsaturated fatty acids to saturated ones. In practice the process is not usually carried to completion. Since the original oils usually contain more than one double bond per molecule (that is, they are poly-unsaturated), the result is usually described as partially hydrogenated vegetable oil, that is some, but usually not all, of the double bonds in each molecule have been reduced.Hydrogenation results in the conversion of liquid vegetable oils to solid or semi-solid fats, such as those present in margarine. Changing the degree of saturation of the fat changes some important physical properties such as the melting point, which is why liquid oils become semi-solid. Semi-solid fats are preferred for baking because the way the fat mixes with flour produces a more desirable texture in the baked product. Since partially hydrogenated vegetable oils are reasonably priced, are available in a wide range of consistencies and have other desirable characteristics such as greater oxidative stability (longer shelf life), they are the predominant fats used in most commercial baked goods. Fat blends formulated for this purpose are called shortenings.
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