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.
Process Objectives of Wort Separation
At mashing we mixed together the grist and hot water. Approximately 80% of the malt has dissolved to form liquid wort. However, 20% remains as a suspension of insoluble malt husks and plant materials. We now need to separate the wort from this slurry. The remaining solids are what we call ‘spent grain’.
We must ensure that the separated wort is clear. Any malt husks will contain tannins (polyphenols), which are bitter. Tannins will reduce the shelf-life of the packaged beer (time for the beer to become visibly cloudy). Any solids will also have attached fatty acid materials (lipids). Lipids will reduce the flavour stability of the packaged beer, causing early staling.
To maximise wort removal, we need to wash out the residual sugars from the spent grain by rinsing it with hot brewing water. We call this process ‘sparging’.
Often, wort separation is the rate limiting step in the brewhouse. Nevertheless, we must reliably complete it within the required cycle time needed for capacity.
In this lesson we will explore the three most common wort separation devices used in brewing. Worldwide, the lauter tun is by far the most common device. However, in larger scale operations, the mash filter is becoming increasingly popular. Both of these wort separation devices have a preceding mash conversion vessel. Yet if we use an infusion mash tun for mashing, this is in fact a dual-purpose vessel. When the mash tun has completed its saccharification stand, we can start wort separation from the mash tun itself; we do not need a second vessel. We will explore these three different approaches to wort separation more thoroughly in a later lesson (wort separation technology).
Our process objectives are to produce a clear wort (with minimal entrained air), to maximise wort recovery, and to consistently achieve this in the required time.
We are now going to examine wort separation in three stages:
1. Forming a spent grain filter bed and pre-clarifying first worts.
2. Collecting clarified strong worts (first worts) and sparged diluted worts (weak worts).
3. Removing and disposing of spent grain.