Lesson 2 - Wort Separation Principles
This lesson deals with the principles of wort separation. Before wort separation, we have completed mash conversion. We will now need to separate the liquid wort from insoluble material. This is mainly the husks from the malt, known as spent grain. We will review the reasons why filtered wort must be clear, and how this affects wort quality. We will examine how the all-important grain filter bed is formed differently, by each of the three most common mash separation devices. These devices are: the lauter tun, the mash filter and the mash tun. We will investigate a typical wort collection profile, which ends with the removal of the spent grain.
Darcy’s Law describes filtration flow rate. We will assess both the variables involved, and what influences them. We will finally use Darcy’s Law to predict the relative flow rates of the three mash separation devices.
Point of refection – reconvene
Welcome back. So, what were your thoughts?
If you remember, the lauter tun had a significant volume of wort under the false floor, which had not passed through the spent grain filter bed. We recirculated these first worts back, until the required wort clarity was achieved. In the case of the mash filter, any wort must pass through the filter cloths. The volume accumulating behind each filter cloth, until the frame is full, is small. When we start the forward flow of first worts, the volume behind the filter cloths is low. It has been filtered of all large particles, but initially, it is not crystal clear. As the filter bed builds in each frame, the compacting husk creates a more effective filter. The strong worts clarity quickly improves, to provide a very clear wort. This appears to compromise wort quality. However, overall, the wort from the mash filter still has the lowest levels of solids and the best clarity. We will look at this in more detail later.
Whilst the filter cloths can deal with the finer husks, if there is high shear at mash transfer this would cause gelling of proteins and β-glucans, which will hinder wort filtration. Low speed mash pumps, low mash velocities and no sharp bends in pipework are therefore important for satisfactory operation.
There are two other differences compared to the lauter tun. Firstly, the strong worts are collected while the mash conversion vessel is still emptying. Secondly, the wort separation flow is driven by the mash pump, whereas the flow through the lauter tun bed is driven by gravity. We will consider the implications of these on brewhouse capacity in a later lesson.