Lautering

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Lautering is a process in brewing beer in which the mash is separated into the clear liquid wort and the residual grain. Lautering usually consists of 3 steps: mashout, recirculation, and sparging.

Mashout is the term for raising the temperature of the mash to 170°F (77°C). This both stops the enzymatic conversion of starches to fermentable sugars, and makes the mash and wort more fluid. Mashout is considered especially necessary if there is at less than 1.5 quarts of water per pound of grain (3 liters of water per kilogram of grain), or if the grain is more than 25% wheat or oats. The mashout step can be done by using external heat, or simply by adding hot water.

Recirculation consists of drawing off wort from the bottom of the mash, and adding it to the top. Lauter tubs typically have slotted bottoms to assist in the filtration process. The mash itself functions much as a sand filter to capture mash debris and proteins. This step is monitored by use of a turbidimeter to measure solids in the wort liquid by their opacity.

Sparging is bubbling water through the grain to extract sugars from the grain. This is a delicate step, as the wrong temperature or pH will extract tannins from the chuff (grain husks) as well, resulting in a bitter brew. Typically, 50% more water is used for sparging as was originally used for mashing. Sparging is typically conducted in a lauter tun.

English sparging drains the wort completely from the mash, after which more water is added, held for a while at 170F and then drained again. The second draining can be used in making a lighter-bodied low-alcohol beer known as Small Beer, or can be added to the first draining.

Home brewers typically use batch sparging, which is similar to English sparging, except that the second batch of water is only held long enough for the grain bed to settle, after which recirculation and draining occurs.

Commercial breweries use continuous process sparging. When the wort reaches a point about an inch above the grainbed, water is added at the same slow rate that wort is being drained. The wort gradually becomes weaker and weaker, and at a certain point, they stop adding water. This results in greater yields.