Plum jam is a fruit preserve made with the whole fruits of the plum tree. Plum jam is typically very sweet, both because plums are sweet and because sugar is usually added to jam as a preservative. It can be used as a spread for breads, muffins, and other baked goods, and some people also like to use plum jam as a layer in cakes, or as a condiment to go with roasted meats, vegetables, and other foods.
Depending on the plums used, plum jam can be red, purple, yellow, or even green in color. Some markets carry plum jam, especially if they carry in an assortment of fruit preserves. Plum jam is also available from companies and stores which specialize in the production of fruit preserves, in which case several different styles of plum jam may be available, along with other styles plum preserves. Cooks can also make plum jam at home, assuming that they are comfortable with the sterile canning process.
Like other jams, plum jam is made from whole crushed or cut fruit. The only part of a plum not used in jam is the pit, because the pit is not edible. Depending on the taste of the cook, the plums may be pitted and cooked whole, or they may be pitted and crushed or cut. The larger the pieces of fruit one begins with, the chunkier the end jam will be.
To make plum jam, cooks simmer plums in water with added sugar until the fruit starts to fall apart, and then they pour the jam into sterilized jars for canning. As the fruit cooks and breaks down, it releases pectin, the substance which causes the jam to firm up. Some cooks like to make their jam smoother by running it through a food processor, ricer, or food mill, while others prefer chunkier jams, deliberately leaving the fruit whole and loose. Ingredients like lemon peels, ginger, and other spices may be added to taste to vary the flavor of the jam.
Like other fruit preserves, plum jam is very perishable. If it is handled properly and canned in sterile jars, it can last up to one year unopened, but as soon as the seal is broken, the clock starts ticking. Plum jam should be stored in the fridge after opening and ideally used within a month, before it has a chance to develop mold or bacterial infestation. If a jar's lid pops up, it is a sign that the jar has been contaminated with harmful bacteria, and it should be discarded, even if the contents look fine.