Grapefruit marmalade is a variety of preserved fruit. Like all marmalades, it is made from the peel of a fruit and the juice. These are typically mixed with some sort of sweetener, often sugar, and boiled. The pectin contained in grapefruit allows the finished marmalade to set to the consistency of jelly. Like other jams and jellies, grapefruit marmalade, if made properly, is shelf-stable and can be stored for years.
The most important difference between marmalades and other jams and jellies is the use of the outer layer of the fruit peel. This portion of a citrus fruit is typically very rich in flavorful essential oils, but can be somewhat bitter. The inner, white pith layer is not used as its taste is bitter and most people find it unpleasant. Like other jellies, grapefruit marmalade uses the juice of the fruit and generally the meat of the fruit as well but not the outer skin of the fruit sections.
Jams and jellies have been made for many hundreds of years. Canning preserves fruit which helped maintain proper nutrition during periods when fresh fruit was not widely available, before refrigeration was invented. Marmalades are especially useful in this regard, as the peel of a fruit is rich in vitamins.
Marmalade is made by cooking finely-sliced outer peal with the meat and juice of the fruit. A relatively small amount of water is added, in most recipes, and the mixture is usually boiled. This mixture is sweetened, often with sugar but sometimes with honey or other sweeteners. The sweetening improves the flavor, as grapefruit marmalade is prone to a degree of bitterness. A finished batch of grapefruit marmalade will gel because the pectin in the skin of the fruit serves as a jelling agent.
Like all preserved fruits, a batch of grapefruit marmalade can be kept for many months, or even years, without the aid of refrigeration. The canning process destroys any microbes, and a sealed jar of preserves will not be subject to decay. Once opened, of course, new microbes will be introduced into the jar, but such preserves have a long refrigerator shelf-life as well.
Grapefruit marmalade is relatively easy to make at home, but commercial varieties are widely available. Some make use of preservatives and color and flavor enhancers. Others, however, simply rely on the natural properties and shelf-life of marmalade.