A lauter tun is the traditional vessel used for separation of the extracted wort. While the basic principle of its operation has remained the same since its first use, technological advances have led to better designed lauter tuns capable of quicker and more complete extraction of the sugars from the grain. The false bottom in a lauter tun has thin slits to hold back the solids and allow liquids to pass through. The solids, not the false bottom, form a filtration medium and hold back small solids, allowing the otherwise cloudy mash to run out of the lauter tun as a clear liquid. The false bottom of a lauter tun is today made of wedge wire, which can provide a free-flow surface of up to 12% of the bottom of the tun. A good quality lauter tun has rotating rake arms with a central drive unit. Cutting blades hang from these arms. The blade is usually wavy and has a plough-like foot which is responsible for proper cutting of the filter bed.