Wort Separation
Mash Tun Separation
Mash tuns are used for infusion mashing where hot water is blended with the grist to create a mash that only has one rest, at saccharification temperature. In a mash tun, the infusion mashing and wort separation are carried out in the mash tun. A mash tun is the traditional piece of equipment used for mash conversion and separation in breweries in United Kingdom and other countries. In most modern breweries, mashing takes place in the mash tun and the wort separation takes place in a separate vessel, the lauter tun (Section 9.2).
Mash Tun Operation
First Wort
After mash-off, the wort is withdrawn through the false bottom of the mash tun like that of a lauter tun. The false bottom acts as a support for the grain bed and does not act as a filter bed. Initially, the flow rate of the dense wort is slow, to avoid pulling down or collapsing the suspended bed. Typically, brewers re-circulate the “first wort” in order to clarify the wort. This is accomplished by re-circulating the first runnings back over top of the grain bed as gently as possible so as not to disturb the grain structure.
Grant. A grant is a small wort collection vessel, open to the air, placed between the lautering vessel and the wort kettle (Figure 9.2).
Sparging
Sparging extracts the fermentable liquid, known as wort, from the mash. Sparge volumes are determined by the brew length and recipe requirements. Sparging begins just after the first worts have been collected and after the mash has settled but before the surface of the mash has become too dry. Additional hot water is added at the same rate that it is removed so that the pressure differential across the bed of grain is kept small between the liquid at the top of the mash and the pressure below the false bottom.
pH Control during Sparging. During lautering (wort separation) buffers are washed out of the mash and there is a tendency for the pH to rise, particularly if bicarbonate is present in the hot (e.g., 75–80°C, 167–176°F) sparge water. If the pH rises above 5.8, it can result in an increase in the extraction of coloring material, undesirable compounds such as harsh-tasting polyphenols, haze-forming starch, lipids, and insoluble proteins from spent grains.
Specific Gravity of the Wort. While sparging is in progress, the gravity of the wort should be periodically checked.
Extract Recovery
The first wort collected during the lauter is high in extract with a wort strength typically between 4- and 6-degrees Plato higher than the target beer. As sparging continues, the sugar content of the wort decreases rapidly. The deeper the grain bed, the more slowly the wort strength declines; thus, more sparging water is needed for extract recovery.
Extract Readings. To determine sugar concentration in wort, small breweries rely on the inexpensive but labor-intensive hydrometer, or the simpler, but more expensive refractometer. Both require samples to be cooled, and both read accurately only at a specific temperature.
Grains-Out
After wort separation is complete, the spent grains are either thrown out by hand, but more typically the grains are swept out of the discharge ports by horizontal arms that rotate over the false bottom of the tun. The spent grains are then collected and transferred by screw conveyor or compressed air to the collection silo.
Click on the following topics for more information on wort separation.
