The brew house is the collective term for the hot processing vessels, including the mash tun and kettle, and may also include a lauter tun or mash filter, a whirlpool, a hop back, an underback, an adjunct cooker, a decoction kettle, and other equipment. To give workers convenient access to the tops of the vessels, a platform or scaffold is often built around the vessels, which sit on the floor below. The capacity of the kettle determines the volume of beer that can be made in a single batch, called the brew length. The function of the brew house is to make wort for the fermentation process.