The lauter tun is the most widely employed wort separation vessel system in North America and Europe. Lauter tuns are, in general, designed much like infusion mash tuns, but they are wider and shallower, as shown in Figure 10.1. Like the mash tun, filtering is through slots in a false bottom that supports the grain bed. However, there are some big difference between mash tuns and lauter tuns. Lauter tuns are suited for use of under-modified malts and high adjunct rates. However, if the recipe has less then 50% malt, there will be insufficient husk material to form an adequate filter bed (15). The grists used in a lauter tun are finer, the mashes are more dilute, and the bed depth shallower all of which helps in extract performance.
In preparation for receiving a mash, the lauter tun is thoroughly rinsed, and underlet with hot water (often 75-78°C) to drive out the air underneath the false bottom (4). The plates of the false bottom are covered with hot water (1.2-2.5 cm) to help spread the mash (4).
Establishing the Grain Filter Bed
Two methods are generally employed to establish the grain filter bed uniformly over the entire floor of the lauter tun. The first method is to operate the lautering machine in a raised position at moderate speed with the blades in "grains out" position until all the mash is transferred. The second method is to operate the machine at a slow speed, with rakes rising slowly in a lautering position as the height of the grain bed increases.
Mash Rest and Underletting
Classical lautering operation provides for a rest period of from 15 to 30 minutes in the lauter tun after the bed is leveled (7). This rest allows the mash to settle prior to recirculation, which is necessary to avoid cloudy wort.
Recirculation of Wort
Before the first wort is run to the brew kettle, it must be re-circulated (known as vorlauf) through the grain bed because it carries finely divided materials from beneath the false bottom. This assists in the establishment of the filter bed and wort clarification.
Collection of First Wort
After the filter bed is established and the wort has reached satisfactory clarity, circulation is stopped and the "first wort" is diverted to the kettle or underback (7).
Sparging and Second Wort Collection
As the first wort is drawn off, sparging is initiated shortly before the wort level reaches the top of the grain bed. The top surface of the grain bed should not be allowed to dry out while sparging.
After the last wort and drainings have left the grain bed, spent grains are removed from the lauter tun and discarded. The grain-out doors are opened, the rakes are raised out of the grain bed, and the knife angles are changed to the grains-out position.
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