Cooling of Herbs.
Once the boiling is complete, it is important to cool the wort quickly. There are several reasons for this;
– to stop the extraction of bitterness from the hops,
– limit the evaporation of flavourings and essential oils,
minimise oxidation,
– prevent the formation of too much DMS,
– give a good cool break,
– limit chill haze,
– avoid wild yeasts and other bacteria.
Extraction of bitterness; a rule of thumb states that every time the temperature drops by 10 degrees Celsius, the extraction decreases by a factor of 10. Or in more understandable Danish; 1 minute at 100 degrees corresponds to 10 minutes at 90 degrees or 100 minutes at 80 degrees etc… is not entirely factual, but gives an idea of the correlation.
Oxidation during mashing, boiling, and cooling causes the formation of undesirable flavour compounds, such as cardboard, wood, or paper.
DMS, or Dimethyl sulphide, is formed from S-methyl methionine (SMM), which is in turn a component of malt. SMM is only found in large quantities in very lightly roasted malts, pilsner and the like, and it is already significantly reduced in pale ale malt.
Cool break, in Danish; koldtrub, is a protein clumping that occurs with very rapid cooling (thermal shock).
Chill haze; a hazy veil of proteins, flavour-neutral.
| Cooling methods: | Disadvantage | Advantage | point |
| Water bath | Slow, easy to aerate and contaminate during stirring. High water consumption | Cheap | 1 |
| Chiller | A bit slow if there isn't going to be a very large water consumption. A bit of a poor cool break. Requires stirring with the risk of oxidation and contamination. | Moderate price | 3 |
| Counter-flow cooler | It only cools the part that is in the cooler, so the first few litres need to be poured back to get down to 85 – 90 degrees. | Extremely effective if the thermal resistance between the wort and cooling water is small. (small material thickness) | 4 |
| Plate cooler | It only cools the part that is in the cooler, so the first few litres need to be poured back to get down to 85 – 90 degrees. Cannot be cleaned internally in the ‘payable’ editions, so the flow becomes poorer over time and they are very difficult to keep clean. Normally copper-soldered. | Extremely effective if the thermal resistance between the wort and cooling water is small. | 2 |
