Lesson 5 - Wort Separation Technology SAQ

**Explain the pressure limitations of the mash tun, lauter tun, and mash filter. For all three devices, demonstrate how their design and operation prevent these limits being exceeded.

Response:

Mash Tun and Lauter Tun

The false slotted floor can only withstand a small vacuum. This is created when the wort collection flow rate from under the false floor is greater than the natural flow through the grain bed. This is dependant on its Darcy variables (e.g. wort viscosity, grain bed permeability). This differential pressure across the false floor is normally limited to 0.1bar (1,000 mmwg) and must not be exceeded during wort collection.

The DP can be monitored in one of two ways. You can monitor the change in level of a manometer tube connected to the under-floor void. Or, alternatively, you could measure the pressure both above and below the false floor.

As the DP increases, the level in the manometer tube drops. In an extreme case, the level in the tube will drop below the false floor level and pull in air to reduce the vacuum. The manometer, as well as indicating DP, also acts as a vacuum breaker. This safeguards the floor from collapsing.

If we are using pressure cells to measure DP across the false floor, then the outlet pipework will be connected by an open vent tube back to the vessel, above its working level. If the DP becomes too high, it will pull in air and thus acts as a vacuum breaker.

The vacuum breaker is a safeguard, but high DP should be avoided during normal operation.

The mash tun DP can only be relieved by reducing wort flow, which will in turn extend cycle time. Continued reduction of wort flow to reduce DP will eventually lead to low flow, or no flow. This situation is called a ‘set bed’. Wort collection is stopped. An underlet of hot water is delivered underneath the false floor by reverse flow through the outlet pipework. The underlet refloats the bed and unclogs the slots in the false floor. Wort collection continues after recirculation, to achieve satisfactory clarity.

The lauter tun is fitted with rakes which can be lowered into the bed to reduce DP to try and maintain flow rate. If, despite this raking, the maximum DP (or minimum manometer level) is reached, wort collection stops. Now a deep bed rake is initiated. The rakes are lowered to floor level to aggressively cut the whole bed for roughly five min. This reduces DP back to near zero. Wort collection recommences after a recirculation, to clarify the fines from under the false floor created by the deep bed rake.

Mash Filter

Instead of draining wort from the grain bed, it is forced through the grain bed and mash filter cloths by the mash pump. The pressure limit for the inlet of mash filter is around 0.5 bar. The unit has a pre-programmed flow rate to follow. However, if grain bed resistance causes the inlet pressure to reach its limit, the unit moves from flow control to pressure control. The mash pump now regulates its speed so as to not exceed the inlet pressure limit. Flow is now lower than target, and cycle time will be extended.