Lesson 4 - Wort Boiling Technology and Process Control
This lesson explores the process of heat transfer during wort boiling, and how it can be controlled. It also considers the design principles of wort boiling systems and how energy use in the brewhouse can be minimised.
Wort Boiling Using Electric Immersion Heaters
Our next method of wort boiling may well be the most common. This is because it is typically the lowest cost system to buy and install and is used in many small breweries, of which there are thousands. If you can run them using renewable electricity produced by solar panels or wind turbines, electrical immersion heaters provide carbon neutral wort boiling!
An immersion heater is an electric element fitted in the side of the kettle, close to its base. Inside the immersion heater an electric current passes through a resistor and electrical energy is converted into heat energy. The heating element is usually encased in stainless steel or titanium.
There is a limit to the size at which immersion heaters are effective and this is around 15 hL. Above this size, heating rates and boil vigour become too low unless you have many heaters.
Immersion heaters have a number of disadvantages. Electricity is currently more costly than gas or other fossil fuels (although this may change in the future) so they are expensive to run. They also need to be replaced a lot more frequently than any other form of wort heating. These two factors mean unless the brewery has a solar farm or large wind turbine, immersion heaters are the most expensive way to boil wort.
They are usually fairly slow at heating the wort to boiling temperature and boil vigour is lower than other systems, leading to long boil times. This can be improved by agitating the wort in the kettle using a pump or mixer, but the lack of turbulent flow over the heating surface and the smaller surface area usually results in a lower rate of heat transfer than that from calandrias.
The lower surface area means to provide the same heat transfer, ΔT needs to be higher which results in increased thermal load/stress and fouling. Another disadvantage is that the heating element may need to be removed for cleaning or to be manually cleaned inside the kettle. Breweries that currently use immersion heaters probably use them because they have to rather than because they want to!