Wort Separation
Lauter Tun Separation
Lauter tun is a vessel used for separating the wort from the solids from decoction mashes and is also used with temperature-programmed and double mashing systems (Figure 9.3). A lauter tun works much like a large sieve, much like the mash tun. It normally has a slotted, perforated floor, also called a false bottom, which holds the spent milled grains, while allowing the wort to filter through the grain bed and collect in the space beneath; the wort then runs to the brew kettle. Mashing occurs in a separate mash mixer or mash tun, in which case the mash must be transferred by a pump to the lauter tun.
Lauter Tun Design
Lauter tuns are, in general, designed much like infusion mash tuns, but they are wider and shallower. This gives better filter performance and allows the use of finer grist, which results in higher extract rates. The wider lauter tun allows the thickness of the grain bed to be significantly reduced. This allows the sparging process to take place faster (with a higher flow rate) while keeping the pressure differential across the bed the same as it would be in the mash tun. The true bottom of the lauter tun may be flat or sloped, or it may be constructed with several concentric valleys with intervening ridges.
Lauter Tun Operation
The control of the lauter tun does not differ greatly in comparison to the mash tun. The fundamentals remain the same although the lauter system does allow functional flexibility.
Foundation Water
In preparation for receiving a mash, the lauter tun is thoroughly rinsed, and underlet with hot water (often 75‒78°C, 167‒172°F). The plates of the false bottom are covered with hot water (approx. 0.375 cm) to help spread the mash.
Mash Off
This step involves pumping the mash from the mash mixer to a dedicated lauter tun. The mash must be well mixed prior to mash off to ensure an even grain bed. This step should be accomplished as gently as possible, preferably using a low shear agitator in the mash mixer and a low shear pump to avoid breaking up the mash particles. This same procedure also applies to a mash tun if equipped with rotating rakes and mash/lauter tuns.
Bed Depth. Bed depth in the lauter tun is generally between 25 to 50 centimeters (cm) (10–20in), though some can have depths up to 55 cm or be as shallow as 20 cm.
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.
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 (Dougherty, 1977). This rest allows the mash to settle prior to recirculation, which is necessary to avoid cloudy wort..
Vorlauf
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. Turbid wort from the grant is transferred from beneath the false bottom and transported to the top of the mash bed via the vorlauf pump. The pumping clears out the area under the false bottom and establishes the filter bed for lautering. If the pumping is too fast; the runoff will cause turbulence between the false and real bottoms.
First Wort
After the filter bed is established and the wort has reached satisfactory clarity, as noted by the clarity of the wort in the grant, circulation is stopped and the “first wort” is diverted to the kettle or underback until the level of the wort in the lauter tun reaches the top of the hydrated grain bed. In some cases, the brewer may direct the wort to the kettle with some fine solids still present, knowing it will reach satisfactory clarity within a few minutes once transfer has started.
Sparging or Second Wort Collection
As the first wort is being transferred to the boil kettle from the lauter tun, the grain is sprayed with hot 71 to 78 degrees C (160–172°F) water to wash additional sugar from the grain, a process called sparging. Sparging can either be continuously or intermittently as desired. Do not sparge with water over 79 degrees C (175°F) since it will result in extraction of harsh polyphenolic compounds (e.g., tannins) from the malt husk.
Sparging and Raking Methods. At this point sparge water is sprayed onto the top to maximize wort extract. The wort collected after sparging is called second wort. Sparge water is proportioned in cycles or is continuous. Some brewers recommend proportioning in cycles of three distinct water additions, the first with 25 percent of the total, the second with 45 percent, and the third with 30 percent.
Flow and Pressure. The principles of fluid flow are relevant to every aspect of beer production, but they are the key issues in wort separation. Differential pressure is the difference in pressure under the false bottom and the pressure above the grain bed. If the differential pressure is too high, the force compresses the gain bed and fills the slots of the false bottom, stopping flow and creating a stuck mash.
Wort Collection
The runoff is transferred either to the kettle or diverted to the underback if the mash kettle is not available. Bottom entry into the kettle allows for a gentler handling of the wort with less chance of oxidation. It is important that the heavy first runnings are not allowed to lie at the bottom of the kettle at high temperatures, which could result in caramelization.
Grains-Out
After wort collection, which is stopped when the wort gravity has fallen to some chosen value, the grains are allowed to drain for about five minutes, to reduce their moisture content. The spent grains are then removed from the lauter tun and discarded.
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