Recently I toured a farm’s harvest processing facilities and mentioned to the farmer that I thought I could automate one of his processes. He challenged me to build such an appliance, so I did.
Using a commercial 1500W hotplate and an Omega temperature controller I fabricated the appliance shown below. A Solid State Relay (SSR) switches power to the hotplate to modulate temperature. The controller operates in four modes (temperature display, constant temperature and ramp/soak program, PID). Since the hot plate operates only in on/off mode I couldn’t use the PID (Proportional Integral Differential) mode.
After using my canning appliance, the happy farmer reported that he was able to control temperature within a +/- 3F range. And this resulted in shortened process times and more uniform product.