The Butter Imposter

• Margarine was originally created in 1869 by a French chemist as a substitute for butter. While originally made with animal fats, today's butter is made from hydrogenated vegetable oils and milk solids. Some margarine brands don't include milk products of any kind, making them an excellent substitute for butter when making frosting for a vegan or dairy-free cake. Although both margarine and butter contain at least 80 percent fat, as directed by the United States Department of Agriculture, the types of fats aren't the same. In fact, margarine has no cholesterol and contains mostly polyunsaturated and monounsaturated fats, which are considered healthier than the saturated fats in butter.

Trading Places

• When substituting margarine for butter in your icing recipe, you can do so in an equal amount. For best results, use solid margarine butter sticks, which have a firmer texture than tub margarine, much as stick butter has a firmer texture than whipped butter. Icing made with tub margarine may be very soft and melt easily on your cake. To make a firmer frosting using tub margarine, skip the liquids, such as milk or water, in your icing recipe. Note that because many types of margarine have a darker yellow tone than butter, your resulting frosting may have more of a yellow hue than frosting made with butter.

The Good, The Bad and The Unhealthy

• Not all brands of margarine are the same and some of them contain trans fats, which are created during the hydrogenation of the vegetable oils the margarine is made from. These fats can increase your "bad" cholesterol, known as low-density lipoprotein cholesterol. Many types of margarine, even stick margarine, have been reformulated to eliminate trans fats. When purchasing your margarine sticks, choose those that are labeled as free of trans fats to keep your frosting as healthy as possible.

Getting Fresh

• Just as butter can expire and turn sour, so can margarine. When storing your buttercream frosting made with margarine, do so in the refrigerator to preserve it for up to two months at a temperature of just below 40 degrees Fahrenheit, recommends the EatByDate website. Margarine-based buttercream icing can also be frozen for up to eight months in the freezer. Defrost it first in the refrigerator and stir it well before using it. Store your cakes frosted with margarine-based buttercream icing in the refrigerator for three days for optimal freshness. If your margarine has an unpleasant odor or has hardened to where you cannot spread it, it has expired and you need to discard it.