;){kind=link}
Wort Separation
Methods of Wort Separation
The method of separating the wort from the mash solids and the equipment used is mainly a matter of choice on the part of the individual brewer, and sometimes of tradition. Wort separation may be carried out by any of a number of different methods: 1) the mash tun, 2) the lauter tun, 3) the mash filter, or 4) the Strainmaster.
Mash Tun
The mash tun has the function of being a combined conversion and wort separation vessel. The mash tun requires the coarsest grind and has the smallest surface filter area and deepest bed of the four wort separation systems. This results in a slower filtration and a poorer extract recovery, but the mash tun can also produce the brightest worts. Mash tuns are well-suited in producing wort from well-modified malt. They are the cheapest in terms of capital expenditures and the simplest to operate, with little or no automation. The combination of these factors makes the mash tun particularly attractive to craft brewers.
The entire cycle from mashing, through wort runoff, sparging, and spent grain removal usually lasts from 3 to 4 hours – 1 hour for mash conversion, followed by 3 hours of runoff, sparging, and grain removal.
Lauter Tun
Like the mash tun, the lauter tun is also equipped with a sparging system to wash the extract from the mash. The top of the tun is usually spherical or conical and fitted with a vent for relieving the vapors of the hot mash to the atmosphere. The bottom of the tun may be flat or sloped, or it may be constructed with several concentric valleys with intervening ridges. Suspended above the true bottom of the tun is a false bottom of milled, slotted, or welded wedge wire steel plates that act as the filtering system. Free surface area (the area through which the wort can flow) varies from 8 to 15% for milled bottoms and up to 25% on welded screen bottoms. The false bottom is not a filter plate but acts as a support for the grain bed.
Typically, false bottoms in craft brewery lauter tuns do not consist of the pie-shaped sections of the machined plate, but rather of the rectangular wedge sections of "wedge"- or "V"- wire screen. Their cost is considerably cheaper than machined bottoms, and the screens perform reasonably well.
The lauter tun, unlike the mash tun, is equipped with rakes to assist mash transfer and for leveling the bed and facilitating filtration of the liquid from the mash. Rakes are more important when the mash is stirred and mixed, such as with temperature-controlled infusion or decoction mashing. Unlike single-temperature infusion mashing, the mash loses its entrained air and sinks onto the false bottom in a dense bed.
Mash Filters
Mash filters, as shown in Figure 10.2, provide a competing system to the lauter tun, but they are not as widely used. Mash filters are very much like plate and frame filters consisting of a series of grid-type plates alternating with hollow frame plates that are suspended on side rails. Each grid plate of the filter is covered on both sides with a monofilament polypropylene cloth.
To initiate the wort separation cycle, the mash filter is flushed, then preheated with hot water. The mash is then pumped into the filter through the top channel, completely filling the filter frames. The entire transfer to the mash filter is completed in 20 to 30 minutes (24). If the filter is underfilled, the efficiency of the extraction process suffers significantly because the sparge water will flow through the empty portion of the chamber (28). Overfilling, on the other hand, results in excessive density, adversely affecting filtration efficiency (28). When the filter is full, the wort collection system is opened, and the wort is drawn horizontally through the filter cloths. The first wort running time is around 12 to 15 minutes. To achieve satisfactory clarity, the wort is recirculated through the filter. Filtration of the main wort takes 20 to 50 minutes. Sparging is initiated after the first wort is partially drained but before the filter cake becomes dry. Sparge water between 75 and 78ºC is pumped into the filter from the bottom and lasts from 90 to 140 minutes (16). Just as with the lauter tun, the mash filter pressure differential is critical. After the last wort, the filter is opened automatically, plate-by-plate, and spent grains fall into a trough with a screw conveyor.
Strainmaster
The Strainmaster, which is not as widely used as the lauter tun or the mash filter, was patented by Anheuser Busch and developed by Nooter Corporation. The Strainmaster consists of a rectangular hopper-bottomed tank that is fitted at the base of the hopper and that has downward opening doors for discharge of spent grains. Within the vessel are header pipes running longitudinally down its length, and attached to these are perforated straining tubes. The header pipes are connected by wort draw-off mains to wort pumps. Wort withdrawal and circulation is initiated when the top row of tubes is covered. The wort is then recycled through the straining tubes to the top of the Strainmaster. The action of drawing wort through the tubes creates a filter bed around the tubes in much the same manner that occurs relative to the lauter tun. Recirculation continues until the desired wort brightness is achieved, then the wort is run to the kettle. As the level of the remaining first wort approaches the mash level, but while the mash is still covered with wort, the sparge is initiated over the top of the bed. Upon completion of the sparge, the grain bed is allowed to drain to relative dryness. The doors are then opened, and the grains fall into the grain receiving tank.
Click on the following topics for more information on wort separation.