We have a small donut shop where we make our donuts from scratch. For our cake donuts, we need to heat fresh milk to ~84°F (give or take, depending on the temp of other ingredients). We do this before mixing in order to get the correct final batter temperature for frying. We've been doing this by weighing our milk in a 4 qt aluminum measuring jug, then placing the jug in a hot water bath (a stock pot filled with hot tap water). We stir the milk and monitor the temperature with a thermometer...
How to heat milk to a precise temperature?
How to heat milk to a precise temperature?