Lesson 4 - Wort Cooling and Oxygenation Technology

On cooling, the protein compounds of our wort interact with the polyphenol compounds to form cold break. The amount produced depends on the type of raw material used, but typically about 15-35% of the total protein content is precipitated as hot and cold break. The formation of the cold break is temperature dependent, only forming significant quantities at temperatures below 20-30^°C. These haze forming compounds then decrease the visual shelf life of our beer.

There may also be some trub (hot break) carry over from the wort clarification system, that we can consider. However, the cold break particles are generally very small and much finer in nature (usually around 0.5 mm) compared to hot break; they thus settle very slowly. As the temperature decreases, however, the quantity of cold break significantly increases. We can also increase the amount of cold break, and indeed the relative sizes of the flocs (to increase their rate of precipitation) by using processing aids. Furthermore, elements of cold break such as protein-polyphenol compounds can form chill hazes (particulate matter that re-dissolves into solution at higher temperatures). It is thus a critical part of achieving a clear beer, with good colloidal stability shelf life.

Excess amounts of trub (hot and cold break) can cause both flavour and process problems, such as:

• The formation of ‘dirty yeast heads’ in top fermenting (ale) yeasts.
• Trub coated yeast affecting fermentation performance.
• The removal of metal ions such as zinc. Zinc is an important yeast enzyme co-factor, so its removal can negatively impact yeast growth and fermentation beer loss.
• Excess lipids, causing flavour stability and foam problems downstream.
• Sulphur flavours such as ‘vegetable’, ‘stewed’ or ‘cabbage-like’.
• Difficulties in filtering and clarifying beer, reducing the shelf life.

The carry-over of trub must be avoided, or limited as much as possible, to achieve consistent fermentations and longer shelf life. This can be achieved through:

• Well managed boils and wort clarification processes.
• Skimming-off from the top via flotation techniques e.g. by floating off the trub using air, or inert gases, in the fermenter.
• Reduce cold break carry over to the pitching yeast.

For top fermenting yeasts we would affect a skimming from the top after 12-24 h. For bottom fermenting yeasts, we would like to see a cropping after 6-12 h. This would remove the prematurely flocculated yeast and the cold break. This should then be discarded. Some breweries, however, do prefer a limited amount of cold break to remain in the fermenter (typically 50 mg/L). They feel this provides a ‘fuller taste’ and also reduces wort loss. Typically, removing 60% of the cold break can cause a 0.2-0.4% wort loss.