The Oxford Companion to Beer definition of
Rye (Secale cereale L.) is a grain type that is strongly linked to the Northern hemisphere, where it historically has been cropped in Germany, Southern Scandinavia, Poland, the Baltic States, and Russia. It is tolerant to poor soils and drought. Rye has a naked grain that takes up water quickly during malting; it requires less water and steeping time than barley. Because rye has no husk, the acrospire of the kernel is vulnerable to damage during the malting process. See acrospire. The crop has mostly been used for food consumption in black bread types. Malted and unmalted rye are also used to produce whiskey (United States), gin (Holland), and beer (Russia, Finland, Germany, Poland). Rye increases the complexity of beer flavor, giving a spicy quality and can lend a rounded, smooth mouthfeel. Rye sometimes adds a reddish tinge to beers in which it is used. Normally, only small quantities of malted rye are used in modern brewing of specialty beers. The usual proportion is about 10%–20% of the malt bill, as in German rye beers (roggenbier). See roggenbier. Higher proportions may be used, but rye contains high levels of protein and beta-glucans, which can cause the mash to become gummy and difficult to run-off. Still, many American craft brewers use rye in relatively high proportions, often seeking to concentrate its unique flavors to the extent practicable. In brewing, rye may be used as whole grains (which must be cooked first), rye malt, or pre-gelatinized flakes.
Briggs, D. E., et al. Brewing: Science and practice. Cambridge: Woodhead Publishing, 2004.
Purseglove, J. W.Tropical crops: Monocotyledons. New York: Longman Group, 1976.