Unveiling the tank
Tips, fun facts, and basic principles of lauter tuns and filtration tanks
By Michael Trommer
The saccharified mash is transferred to the lauter tun. The insoluble parts of the mash settle on the bottom of the tank on a perforated (false) bottom. The soluble part goes through the openings or holes of the false bottom and is subsequently sent to the boiling tank, via transfer pump.
For a given spent grain cake, it is possible to calculate the theoretical filtration flow rate by using the following formula:
In the time unit, the volume of wort is inversely proportional to the wort viscosity (n) and the length (I) of the capillary. The volume of wort is directly proportional to the pressure difference (ΔP) and the squared radius (r) of the active pores. Using that equation, it can be calculated the flow rate of a capillary, pore through which the wort passes. The above formula is applied under ideal conditions. The wort filtration changes the pressure difference (ΔP) and the porosity of the spent grain cake, consequently changing the flow rate passing through the capillary (cake pores) as well.
The structure of the lauter tun and its equipment influences the filtration rate and the clarity of the wort, as well as the sugar
The tank is round; in rare occasions, it can be rectangular or square. The tank walls are usually cylindrical. The material may be copper or stainless steel. Thermal insulation is important (76° to 78°C), in order to avoid cooling of the mash contained in the tank. For the insulation, it is used rock wool, glass wool, or an organic interwoven material, coated with a metallic layer, to seal off the tank against humidity. The real bottom of the tank also needs thermal coating.
Heating creates convection currents, which impairs the lautering process. Therefore, there must not be steam heating jackets or hot water to heat up the tank.
On the top of the tank, there is a cover (dome), which must contain a steam removal system (chimney).
The lauter tun must be fixated to the floor in a way to prevent shaking or moving, so the spent grain cake does not settle on the bottom and the wort pass through the slots of the false bottom.
The bottom of the tank, as well as the false bottom, must be leveled to achieve homogeneous extraction all over the filtration area. The leveling must be checked periodically.
The filtration tank depends on the volume of grist added into the wort tank, that is, the total amount of wort. Therefore, for each 100 kg of malt, there must be 800 liters of space inside the filtration tank. In conventional systems, the height of the spent grain layer must be between 30 to 40 cm. In high spent grain tank type, that height must be between 50 and 65 cm.
The finer the ground malted barley, the shorter the height of the spent grain cake for the same amount of raw material. The ideal case for a given amount would be large spent grain cake height and low hectoliter weight.
In this type of lautering tun, it is appropriate a wet or conditioned grinding, moistened with water at temperatures between 35°C and 50°C.
The false bottom is usually made of stainless steel, with 0.7 mm slots or holes on the top and approximately 18% of area for passage of liquid on the false bottom.
As reference, the following are parameters for loading the tank or a new project:
ü 160 to 175 kg/m² of non-conditioned dry ground malt;
ü 175 to 200 kg/m² of conditioned ground malt;
ü 210 to 280 kg/m², in case of wet grinding.
The false bottom must be 20 mm above the real bottom of the tank. The slots on the superficial part have a width of 0.7 mm. That width increases towards the lower part, reaching 3 to 4 mm in the lowest part. They have the shape of an inverted bell.
On the real bottom of the filtration tank, there must be one outlet tube for the filtered wort per square meter. The tubes must have a diameter of 25 to 45 mm, and be connected to a central system that receives all the filtered wort, without getting in contact with the air. A system of probes or CPU may ensure that the wort do not come into contact with the air; in the event of air infiltration, the transfer pump from the filtration tank to the boiling tank is turned off.
1 - Mash piping
2 - Mash piping valve
3 - Spent grain cake rake
4 - Spent grain cake cutter
5 - Plate for automatic spent grain removal
6 - Raking reducer
7 - Filtered wort piping
8 - Filtered wort collector
9 - Filtered wort collector outlet to the boiling tank
10 - Sparging water piping
11 - CIP piping
12 - Spent grain removal manhole
13 - Worm-threaded hopper to remove the spent grains from the tank to the silo
14 - Tank insulation
15 - Check manhole
16 - Tank internal light
The amount of filtrated wort that passes through every pipe varies according to the height of the liquid inside the tank: from 0.1 to 1.5 m at a rate of 1.4 to 4.4 m/s.
Extracting the sugars from parts farther away from the center of the tank bottom is harder than from closer to the center of the filtration tank. In order to achieve that in large-size tanks, the tank is divided in two or three zones, and the pipes send the filtered liquid to a pipe with greater diameter that goes around the tank, on the lower part. This liquid will be subsequently mixed with the wort of other zones, in a buffer tank or a pipe with greater diameter, which sends the filtered wort for the boiling tank via transfer pump.
ü The process of transferring the mash to the mashing tank must take 8 to 10 minutes, with a rate of 0.3 to 0.4 m/s. The point of this rate is to distribute the spent grain homogeneously, without further breaking the husks.
ü Initiate filtration slowly. The 20 minutes of primary wort filtration must be performed with reduced flow, for subsequent increase of filtration to 0.35 to 0.40 hl/min.
ü Parameters for an ideal spent grain cake, with good filterability:
· Dry grinding: 30 to 35 cm;
· Conditioned, using tepid water: 35 to 40 cm;
ü The flow of the wort in the real bottom (pump) outlet may not be greater than the wort flow passing through the spent grain bed. In this case, between the false and the real bottoms, formation of negative pressure occurs, compacting the spent grains against the false bottom.
ü The removal of the remaining extract from the sparging waters must be performed using minimum water, so as not to excessively remove the tannins, which can cause deteriorate the final quality of the finished beer (astringency).
ü The temperature of the last water extract must be between 0.8° and 1.2°P.
ü In classic filtration, the sparging water dosing system must be located 1 meter above the spent grain cake, in order to create physical friction and help saturate the water with the sugars.
ü The cutting blades of the cake must be at a distance of 20 cm from one another, and their ends must be in the shape of a plow. The blades must cut the cake, rather than push it.
ü The speed of the cake cutter must be approximately 2.5 to 3.5 m/min.
ü According to the size of the lauter tun, the number of rake arms should be the following:
· Above 3 tons – 3 arms;
· Above 6 tons – 4 arms;
· Above 10 tons – 6 arms;
· Under 3 tons – 2 arms;
ü The height of the spent grain cake layer must reach between 30 and 40 cm.
ü The temperature of the last sparging water must be between 0.8° and 1.2°P.
ü After the end of the filtration, the extract contained in the spent grain cake must be at around 0.7° to 0.9°P. This temperature must be measured in the center and sides of the cake.
False bottom of the lauter tun, with free slots for the passage of the filtered wort. Those slots measure 0.7 mm on the upper part and have the shape of an inverted bell.
By obtaining those values in your filtration tank or lauter tun, the tank is well dimensioned and properly operated. The tank that has greater impact in the mashing yield, including in financial matters, is the filtration tank. For that reason, special care should be had with it.