Lesson 6 - Wort Separation Process Control

Wort separation impacts on wort quality. We need to minimise air entrainment. Our wort needs to be clear and free of solids to limit lipid carryover. We need to minimise dissolving of polyphenols.

Minimisation of Entrained Air

This is dependent on which type of wort separation device we are using.

The mash tun has the largest air entrainment. It is filled from above and the grist is not saturated with water. 

The lauter tun offers significantly reduced air entrainment with mash entry at low-level and generally sparging onto a flooded grain bed.

The mash filter offers the lowest air entrainment. It is initially exposed to the air being displaced out of the filter chambers, but thereafter the system is totally enclosed, and the mash is only exposed to the oxygen in the sparge water.

The brewing hot water for sparge will normally be in tank at say 82˚C; at this temperature it will contain very little entrained air. However, on transfer it will need to be attemperated to the sparge temperature of 76-78˚C. This is done by blending in cold brewing water, which may have significant levels of dissolved air.

Another potential source of air entrainment with the mash tun and lauter tun is from the under-floor vacuum breaker. This is designed to pull in air if high DP creates too high a vacuum under the false floor. If this is happening, we will see air bubbles in the wort outlet main sight glass.  It will also register as high haze on an in-line turbidity meter.   

Wort Clarity and Settleable Solids 

Haze measurement is primarily indicating the presence of colloidal material at the 0-10-micron range. This will be mainly protein and carbohydrate. Significant quantities of the protein will denature at boiling and be separated as trub. The carbohydrate fraction will continue forward and be present in the beer to cause beer filtration difficulties. So, a clear wort is highly desirable.  

Lipids are detrimental to the flavour stability of our finished beer. They are surface active and will adsorb to the surfaces of particulate matter. So, by ensuring clear worts, we are leaving behind the lipids in the spent grain.

Wort clarity is dependent on the wort separation device in use and typical figures are:

Table: Typical wort clarity and lipid levels

Wort Clarity Problems

If our wort outlet is fitted with an in-line turbidity meter, then we can trend the history of wort haze for the entire wort collection period. We can determine if there have been any abnormal high haze incidents. If we do not have an in-line meter, we can take spot check samples and make a visual assessment or measure haze off-line. An assessment of clarity at half-way through strong worts, and at last runnings, is suggested as minimum for routine monitoring.

The haze meter is reading the presence of colloids in the 0-10-micron size range. It does not detect larger particulates. Therefore, we also need to check for settleable solids. This is determined by collating together representative samples throughout the wort collection, keeping them at hot wort temperature, combining them into a 1 litre Imhoff cone, and determining the volume of settleable solids. It is important that this is done at hot wort temperature, as at lower temperatures protein will come out of solution and register as haze. This haze was not present during wort collection and therefore could not be removed.

Sub-standard wort clarity will generally be associated with problematic wort separation.

At the pre-programmed flow rate, if the DP is too high, the lauter tun will initiate a deep bed rake to relieve this. Each deep bed rake disrupts the grain bed and despite first worts recirculation, extra solids will inevitably get through. This could be avoided by reducing the target wort collection flow rate, but this will also increase the cycle time.

The mash tun does not have rakes and can only avoid excessive DP by reducing wort flow. Failure to do this will result in a set bed, which will require an underlet. The underlet will disrupt the bed and result in less clear worts going forward while it is reforming.

The mash filter will see the inlet pressure rise to its limit, and then will reduce flow to ensure this limit is not exceeded. This will not affect wort clarity but will extend cycle time.

Poor wort clarity unrelated to difficult wort separation may instead be caused by mechanical failure:

• A false floor plate incorrectly seated/aligned will continually allow through solids.
• A torn mash filter cloth will continually allow through solids.

Extraction of Polyphenols

The level of polyphenols will depend on the wort separation device used. Typical figures are:

Table: Typical wort polyphenol levels

The polyphenols are mostly in the malt husk fraction. The mash tun, which uses the coarsest grind, has the lowest polyphenol level. Compared to the mash tun there is a 9% polyphenol level increase for the lauter tun, and an 18% increase for the mash filter. This may or may not be an issue depending on the expected shelf-life of the beer. (Polyphenols can be reduced downstream by treatment with process aids at beer filtration.)

If polyphenol levels are higher than normal, then the pH of the last wort runnings should be checked. If this has increased, more polyphenols will be extracted. Ideally, last runnings should not be greater than pH 6, to minimise extraction of polyphenols.