Sparging is the spraying of fresh hot liquor (brewing water) onto a mash to rinse out residual sugars. It is essential to achieving desirable efficiency of sugar extraction.

Once the malt enzymes have digested starch into sugars, the mash must be drained and separated from the residual solids, particularly the malt husks. The sugary wort produced by mashing will be filtered by these solids which are held on the mash or lauter plates; much will remain on the surface and crevices of the husks. See lautering. Removing this residue requires rinsing with fresh brewing liquor.

Before sparging became mechanized, grains were rinsed by refilling the mash tun with fresh liquor, stirring, and then re-draining. This may have been repeated a number of times until no further sugars could be removed. Historically a number of beers of different strengths could be produced from a single mash by this means, which is called the “parti-gyle system.” See parti-gyle.

Mechanical sparging developed as a more efficient system whereby liquor was sprayed onto the top of the mash continuously and drained off from the bottom. Wort was collected continuously in the kettle and a single brew of a target strength was produced.

Successful sparging requires a careful matching of inflow and outflow as too fast or too slow a sparge will result in an overflow or a dry mash. In either of these circumstances, lautering can be inefficient or cease entirely. It is also important to ensure that the sparging liquor is suitably treated, if necessary, to maintain a low pH in the mash. Too high a pH can result in excessive extraction of tannins and silicates from the grain husk, which can give the finished beer an undesirable astringency.