Lesson 2 - Wort Clarification Technology and Process Control

Before wort is clarified it is full of suspended material. In wort clarification we need to remove the suspended material. As you would expect, the main goal of wort clarification is to produce clear wort.

We don’t do this because clear wort looks nicer than turbid wort. The suspended material contains substances that can reduce foam stability, make the beer taste bad and damage the fermentation and yeast crop. There is some debate about the degree of clarity required to make great beer. Some argue that crystal clear wort is lacking in nutrients (specifically lipids) that yeast needs and as a result fermentation will be ineffective. The level of clarity has been shown to affect flavour, so the turbidity level of the wort should be consistent to ensure that fermentation and hence the beer remains consistent. Haze levels of 2-3 EBC for fully clarified wort are specified by many commercial breweries but there is wide variation across the industry.

When clarifying wort we are removing trub and spent hops. Some class spent hops as part of trub while others consider them separately. Here’s a reminder of what trub contains.

Table: Characteristics of trub

The word trub has German origins, from trübe (also trüb), which means cloudy. This term is used in brewing and wine making as trübstoff (cloudy + material) and weintrüb (wine + cloudy) respectively. Trub may also refer to lees, a layer of sediment left at the bottom of the fermenter after the yeast has completed the bulk of the fermentation.

Typically, the amount of trub formed (excluding the hop debris component) is 0.2-0.4% of the hot wort volume, which is 0.15-0.4 kg/hL. The total weight of material we must remove depends on the amount and type of hop products used. 

Larger particles settle out of wort more easily, so we look to maximise the size of trub flocs. We typically like to produce flocs of 5-10 mm in diameter. Transferring wort through pumps and restrictions produces shear forces that can break up flocs, reducing their size (typically to 20-80 μm).

We can assess floc size visually by taking a sample of wort from the wort separation device before sedimentation or filtration has occurred. The wort in an Imhoff cone should be visually clear and the flocs suspended in the wort 5-10 mm in diameter. Floc formation is as much to do with boil effectiveness as wort separation, so an effective boil is vital.

With everything in brewing, time is money and we need to ensure the process takes the minimum possible time, so that we can move on to the next brew. Shorter process time is also important to minimise the thermal load on the wort, colour and flavour pick up and the likelihood of producing more DMS from its precursor.

The objectives of wort clarification are:

• Separate trub and spent hops from wort
• Produce wort of the required clarity
• Remove and dispose of trub and spent hops
• Minimise thermal load
• Minimise heat derived colour and flavour formation
• Minimise carry-over of foam negative compounds (e.g. lipids and fatty acids)
• Minimise time taken