lautering

Lautering is a step in beer brewing in which the sugary wort is separated from the solid spent grains after mashing. The process typically takes place in a lauter tun, a vessel equipped with a perforated bottom or a filtration bed that acts as a filter while allowing liquid to pass and solids to be retained.

In lautering, the mash bed is first clarified by recirculating the first runnings back onto the top of the bed (often called vorlauf). This helps to settle particles, strengthen the filter, and improve wort clarity. After recirculation, wort is drained from the bottom of the bed into the kettle. The grain bed is then sparged, or rinsed, with hot water to extract remaining fermentable sugars. This rinsing can be done as a batch sparge (adding sparge water, draining, repeating) or as a continuous fly sparge (water is added gradually while draining continues).

Efficiency during lautering depends on factors such as grain crush, mash thickness, water chemistry, and temperature control, as well as the design of the lauter tun. Some brewers use a combined mash/lauter tun, while others employ separate vessels.

The outcome of lautering is a clarified wort with most fermentable sugars extracted from the grain, ready for boiling, hopping, and fermentation. Spent grains are separated and can be used as animal feed or other byproducts.