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1540s, "action of making short," verbal noun from shorten. Meaning "butter or other fat used in baking" (1796) is from shorten in the sense "make crumbly" (1733), from short (adj.) in the secondary sense of "easily crumbled" (early 15c.), which perhaps arose via the notion of "having short fibers." This is the short in shortbread and shortcake.
fats and oils of animal or vegetable origin used in most doughs and batters to impart crisp and crumbly texture to baked products and to increase the plasticity, or workability, of doughs. Important commercial shortenings include butter, lard, vegetable oils, processed shortenings, and margarine. For most baking purposes, desirable characteristics include bland or pleasant flavour; freedom from objectionable odour; light or clear colour; a high degree of plasticity; long storage life; and good shortening power, or ability to weaken and lubricate the structure of baked products to produce tenderness. Firm fats produce flaky pastry; oils yield more compact pastry. The proportion of shortening in doughs and batters varies according to the product, with breads and rolls containing about 1-2 percent, cakes containing 10-20 percent, and piecrusts containing over 30 percent. Increasing shortening proportions increases tenderness, but very high proportions may cause cakes to fall