Lesson 4 - Wort Cooling and Oxygenation Technology

We will now focus on a few critical parameters that must be met by our wort cooling system.

Let us first revisit coolships. These very large, shallow vessels were used to rapidly cool wort. We say rapidly (even up to 12 h), as it is incomparable to today’s technology and efficiencies. Nonetheless, it still achieved a fast temperature drop due to the very large surface area, allowing good evaporative cooling.

Coolships use evaporative cooling. This is where latent heat is transferred from the wort as it cools, to the moisture in the air, as the steam (water vapour) rises from the hot wort, via evaporation. Latent heat is only transferred when there is a change of phase (e.g. a liquid to a vapour) without a change in temperature. This is opposed to sensible heat, where there is no change of phase, but there is a change in temperature.

Coolships were most often situated at a high point in the brewery, with a good airflow over the wort. They would often be used in combination with an open trickle cooler, over which the wort would run once it reached about 40^°C.

Both latent and sensible heats refer to the type of heat transfers between a body and its surroundings. Latent heat is defined as the heat needed to achieve a change in phase (solid, liquid, vapour) without a change in temperature. Latent heat is ‘hidden’ heat energy, as we do not feel a temperature change. However, we do feel (sense) a temperature change with sensible heat, as there is no phase change.

There are other evaporative cooling technologies, such as falling-film evaporators, steam stripping columns or vacuum evaporators. These technologies have higher energy requirements and can also influence wort composition using significant changes in the wort temperature profile. A later design of the coolship, called the dynamic coolship, uses a smaller closed vessel and a gentle whirlpool action to enhance evaporation. They come without additional energy requirements.

If we enhance the evaporation of a system, we will then make evaporative cooling more effective. This can be achieved by:

• Lowering ambient humidity.
• Decreasing atmospheric pressure.
• Increasing surface area of evaporation.
• Choosing different evaporative media
• Adding air movement.

Hygiene would have been a big challenge by today’s standards. However, these systems were mostly used for specific beer styles, and still are today e.g. for the classic lambic beers of Pajottenland and Brussels. These beers do not focus on wort clarity or wort oxygen levels and are instead sold on the basis of the flavour variety produced by the invading microflora and fauna!