Lautering is the process in ale making where sweet wort (liquid) is separated from the residual grain or mash. Mash is the mixture of hot water and crushed grain which is used in making malt drinks such as ale. The liquid that separates from the grain after lautering is called the wort. It contains the sugars that will be fermented by the yeast (which is added later). There are normally three steps in lautering: mashout, recirculation and sparging.
In mashout, the temperature of the mash is brought up to 170oF (77oC) in order prevent the starches from being transformed into fermentable sugars. A lot of home brewers often skip this step without any consequences, but it becomes necessary when the mash reaches a ratio of 1.5 quarts water per pound of grain (3 liters of water per kilogram of grain).
Temperature should also increase when the mash becomes unusually thick. You would know this if the mash is already composed of more than 25% wheat or oats. Mashout allows the grainbed and the wort to become more fluid thereby preventing what is called a stuck sparge. A set mash wherein no more fluid is flowing from the grainbed is also referred to as a stuck sparge. Mashout is done by apllying external heat or by adding hot water to the grain.
The second step in lautering is recirculation. At this phase, the wort is drawn out of the grainbed and poured back on top for a second draining. A lauter tun is a vessel that contains the mash. It has a false bottom or a manifold that allows the wort to drain out from the mash. This first batch of wort is usually murky or cloudy at first but becomes clear quite quickly.
Sparging, which is the third step of lautering, is the process of rinsing the grainbed after the wort is collected. This would allow sugar to be extracted from the mixture. Literally, the word means sprinkling, and is a throw-back to the practice of ancient priests of using asparagus spears to sprinkle holy water.
Sparging is a delicate procedure where temperature and pH is continuously monitored. If the temperature goes above 170oF (77oC), for example, the tannins (a plant chemical) become soluble and are thus dissolved into the wort, giving the wort an caustic taste.
Sparging takes from ½ to 2 ½ hours to finish depending on the amount of grain and lautering system used. Normally, 50% more water is used in sparging compared to the amount of water uses during the mashout stage.
There are three methods of sparging: English sparging, batch sparging and continuous sparging. In English sparging, the wort is allowed to drain completely from the mash before more water is added for a second draining. The mash is then held at 170oF (77oC) before it is allowed to drain out once more. Batch sparging, which is used by most home brewers in the United States, is done by adding the full volume of sparge water to the mash and then drained out. Continuous sparging, which is used most commonly by commercial breweries, allows the wort to drain out until only an inch is left above the level of the grainbed. Then water is added at the rate at which the wort is draining, thus keeping the wort level at one inch above the grainbed at all times.