Hi Billy,
You will need to jacket the vat, so you can either introduce steam or hot water into the jacket which will then transfer heat to the inside of the cheese Vat. You will need to insulate the outside of the jacket to minimise heat loss to atmosphere. It would be worth researching the best form of jacket for heat transfer.
You can set up a closed loop with recirculating hot water to control the temperature of the Vat.
Some Vats even have a water jacket with built in electric heating elements that heat the jacket.
I am not really sure how temperature is controlled with a steam boiler. However if you are making the jacket yourself I would advise against it unless your brother is able to pressure test the jacket. Steam burns are very nasty if something goes wrong.
Good luck. What ever you decide on doing you should document your build and solution on the forum to help the next person who has the same issue. I am very curious to see how you build your vat.
Mathew
