Why cooling the wort?
Wort cooling is a stage of the brewing process performed using heat exchangers
By Michael Trommer
The boiled wort, after receiving addition of hops, must be cooled down. In case of low fermentation, the temperature has to be lowered to 4 to 7°C; in forced processes, 10 to 17°C; and to 18 to 24°C for high fermentation.
The role of the heat exchanger is to bring the wort to the oxygen absorption temperature, which must be enough for the yeast to start fermentation.
The wort cooling stage is simply a physical process, in which, via heat exchangers, it occurs gain of hot water and wort at the desired temperature.
The “sterile” hot wort is processed at temperatures in which propagation of microorganisms is possible.
Equipment for wort cooling
These days, cooling is performed exclusively through closed systems: tubular and plate exchangers. Traditionally, some breweries do not use plate coolers.
Tubular coolers are made of two parts. The first part has water at room temperature (supply water) and the second part contains brine, glycol, or an alcoholic solution.
The wort flows through copper or stainless steel tubes.
Wort heat waste is higher in comparison with plate heat exchangers. In addition, cleaning tubular coolers is trickier.
Plate coolers consist of packs of stainless steel plates, in which wort flows on one side and, on the other, there is a turbulent flow of coolant. The plates are sealed to one another using rubber profiles between them.
On the corners of the plates, there are slots for the fluid to pass though, which form distribution channels. In the first stage, pre-chilling using process water at room temperature occurs and afterward, in the second stage, using cold water, glycol, or an alcoholic solution.
Between both parts, there is a passage through which the heat exchanger receives cold process water, glycol, or an alcoholic solution from the process. The coolant is sent in counterflow to the wort, and gets heated up by the wort heat.
In closed cooling processes, the ratio between wort and process water at room temperature, during the first stage, is 1:1.1. The water then reaches 80 to 82°C and is used by the brewery in the mashing and sterilization processes. A cooler manufactured to work under these conditions is submitted to a pressure of 2.5 to 4.0 bar. For safety reasons, the exchanger must be able to withstand 10 bar of pressure.
Cooling of the wort at 95°C to the fermentation starting temperature must take place within 40 to 60 minutes.
The fermentation starting temperature of the wort cannot be reached with the use of supply water. Therefore, the water needs to be cooled from 0 down to +2°C, using a chiller or ice bank.
As shown above, the wort can be cooled in two stages (pre-chilling and chilling) or using a one-stage system.
In the pre-chilling system, the wort reaches 25 to 30°C. In this stage, the water starts at 80 to 82°C. In the second stage, the wort reaches oxygen absorption or fermentation starting temperature with cold water at 1 to 2°C. This cold water used to cool down the wort circulates in a closed cycle, because, after thermal exchange with the wort, it will be colder than the process water. After that, the water returns to the supply.
Two-stage heat exchanger
Nowadays, it is occurring a slow migration to the one-stage system, which uses cold water at 1 to 2°C. Through thermal exchange with the wort at approximately 95°C, the water must reach 80 to 82°C. These values should be obtained in a well-dimensioned heat exchange system between wort and water.
One-stage heat exchanger
Plate heat exchanger with two-stage cooling (pre-chilling and chilling):
Plate Heat exchanger with one-stage cooling:
In order to obtain a good heat exchange, the fluids have to be able to circulate quickly, but with enough contact time so they can exchange heat. The following are also recommended: