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An oast, oast house or hop kiln is a building designed for kilning (drying) hops as part of the brewing process. They can be found in most hop-growing (and former hop-growing) areas and are often good examples of vernacular architecture. Many redundant oasts have been converted into houses. The names oast and oast house are used interchangeably in Kent and Sussex. In Surrey, Hampshire, Herefordshire and Worcestershire they are called hop kilns.

They consist of a rectangular one- or two-storey building (the "stowage") and one or more kilns in which the hops were spread out to be dried by hot air rising from a wood or charcoal fire below. The drying floors were thin and perforated to permit the heat to pass through and escape through a cowl in the roof which turned with the wind. The freshly picked hops from the fields were raked in to dry and then raked out to cool before being bagged up and sent to the brewery.
The purpose of an oast is to dry hops. This is achieved by the use of a flow of heated air through the kiln, rather than a firing process.

Hops were picked in the hop gardens by gangs of pickers, who worked on a piece work basis and earned a fixed rate per bushel. The green hops were put into large hessian sacks called pokes (in Kent) or green sacks (West Midlands). These would be taken to the oast and brought into the stowage at first floor level. Some oasts had a man-powered hoist for this purpose, consisting of a pulley of some 5 feet (1.52 m) diameter on an axle to which a rope or chain was attached.

The green hops when freshly picked had a moisture content of approximately 80%. This needed to be reduced to 6%, although the moisture content would subsequently rise to 10% during storage.

The green hops were spread out in the kilns. The floors were generally of 1+1⁄4-inch (32 mm) square battens nailed at right angles across the joists, placed so that there was a similar gap between each batten, and covered with a horsehair cloth. The hops would be spread some 12 inches (300 mm) deep, the kiln doors closed and the furnace lit. When the hops were judged to be dried, the furnace would be extinguished and the hops removed from the kiln using a scuppet, which was a large wooden framed shovel with a hessian base. The hops would be spread out on the stowage floor to cool, and would then be pressed into large jute sacks called pockets with a hop press. Each pocket contained the produce of about 150 imperial bushels (5,500 L) of green hops. It weighed a hundredweight and a quarter (140 pounds (64 kg)) and was marked with the grower's details, this being required under The Hop (Prevention of Fraud) Act, 1866.

The pockets were then sent to market, where the brewers would buy them and use the dried hops in the beer-making process to add flavour and act as a preservative.En savoir plus