I never thought of Rhubarb as a fruit but here's the story!
Rhubarb is a group of plants that belong to the genus Rheum in the family Polygonaceae. They are herbaceous perennial plants growing from short, thick rhizomes. They have large leaves that are somewhat triangular-shaped with long fleshy petioles. They have small flowers grouped in large compound leafy greenish-white to rose-red inflorescences.
Although the leaves are toxic, various parts of the plants have medicinal and culinary uses. The traditional Chinese pharmacopeia features rhubarb. In culinary use, fresh raw stalks are crisp (similar to celery) with a strong tart taste; most commonly the plant's stalks are cooked and used in pies and other foods for their tart flavour. A number of varieties have been domesticated for human consumption, most of which are recognised as Rheum x hybridum by the Royal Horticultural Society.
Rhubarb is usually considered to be a vegetable; however, in the United States, a New York court decided in 1947 that since it was used in the United States as a fruit it was to be counted as a fruit for the purposes of regulations and duties. A side effect was a reduction in taxes paid.
Rhubarb is now grown in many areas and thanks to greenhouse production is available throughout much of the year. Rhubarb grown in hothouses (heated greenhouses) is called hothouse rhubarb and is typically made available at consumer markets in early spring, before outdoor cultivated rhubarb is available. Hothouse rhubarb is usually brighter red, more tender and sweeter-tasting than cultivated rhubarb. In temperate climates, rhubarb is one of the first food plants to be ready for harvest, usually in mid- to late spring (April/May in the northern hemisphere, October/November in the southern hemisphere), and the season for field-grown plants lasts until September. In the northwestern US states of Oregon and Washington, there are typically two harvests: one from late April to May and another from late June into July. Rhubarb is ready to be consumed as soon as it is harvested, and freshly cut stalks will be firm and glossy.
Rhubarb will grow year-round in warm climates, but in temperate climate the above ground portion of the plant completely withers away at the onset of freezing temperature; the plant grows from the root at the return of warm weather. Rhubarb growth can be forced or encouraged to grow early by raising the local temperature, usually by placing an upturned bucket over the new shoots. Because rhubarb is a seasonal plant, obtaining fresh rhubarb out of season is difficult in colder climates, such as in the UK.
Rhubarb can successfully be planted in containers, so long as the container is large enough to accommodate a season's growth.
The color of the rhubarb stalks can vary from the commonly associated crimson red, through speckled light pink, to simply light green. Rhubarb stalks are poetically described as crimson stalks. The color results from the presence of anthocyanins, and varies according to both rhubarb variety and production technique. The color is not related to its suitability for cooking. The green-stalked rhubarb is more robust and has a higher yield, but the red-colored stalks are much more popular with consumers.
One way is to cut up the stalks into 1 inch (2.5 cm) pieces and stew them (boil in water); it is only necessary to barely cover the stalks with water because rhubarb stalks contain a great deal of water; add 1/2 to 3/4 cup of sugar for each pound of rhubarb, then add cinnamon and/or nutmeg to taste. Sometimes a tablespoon of lime juice or lemon juice is added. The sliced stalks are boiled until soft. An alternative method is to simmer slowly without adding water, letting the rhubarb cook in its own juice.
At this stage, cooked with strawberries or apples as a sweetener, or with stem or root ginger, rhubarb makes excellent jam. Other fruits, with the addition of pectin (or using sugar with pectin already added), can be added to rhubarb at this stage to make a variety of jams: the fruit is added at a ratio of two parts fruit to one part rhubarb, consisting of strawberries, raspberries, or chopped plums, apricots, or apples. Boiling should continue for at least ten minutes after all fruit is completely softened, depending on whether a simple refrigerated jam is made, or if (with longer cooking) jam is to be bottled for a long shelf life.
To make a "sauce" of rhubarb (to which dried fruit could be added near the end), continue simmering 45 minutes to one hour at medium heat, until the sauce is mostly smooth and the remaining discrete stalks can easily be pierced with a fork, which yield a smooth tart-sweet sauce with a flavor similar to sweet and sour sauce. This sauce is called rhubarb sauce, analogous to apple sauce. Another name for it is stewed rhubarb. Like apple sauce, this sauce is usually stored in the refrigerator and eaten cold. The sauce, when stewed over medium heat only a short time (about 20 minutes) and with only a little water so that the rhubarb stalks stay mostly discrete, may be used as filling for pies (see rhubarb pie), tarts, and crumbles. Sometimes stewed strawberries are mixed with the rhubarb to make strawberry-rhubarb pie. This common use has led to the slang term for rhubarb, "pie plant", by which name it was more commonly known in the United States in the latter nineteenth century. In her novella The First Four Years, American author Laura Ingalls Wilder refers to rhubarb as "pie plant". It can also be used to make a fruit wine.
