Denwood
Well-known member
I posted this up in my thread, but am throwing the information here for google. I found various bits of information on adjusting popcorn kettle thermostats, but none that bring everything together. Hopefully this helps someone out there 
Problem: I noticed, after a few batches on this new machine, that the popcorn was chewy and yields seemed low. Additionally, quite a few un-popped kernels were left in the kettle. The kernels looked slightly burnt and were partially split.
Solution: Kettle temperature needed to be lowered.
It took me some experimentation and reading to figure out that the kettle temperature was actually too high. The manufacturer did send me a guide to adjust but honestly, it was useless, aside from the fact that they confirmed both thermostats need to adjusted together. There was no indication of a target temp. They did advise that boiling a cup of water should take 3 minutes, but this tells you nothing if the thermostat is set too high..it just confirms the element is working. Guessing the temp is potentially dangerous as once you get into the 500 F range, an oil fire could occur. The factory setting was too hot by about 100 F. Turns out popcorn kernels like to pop around 360 F (180 C) according to some published science experiments.
How to adjust the kettle temperature thermostat on a Great Northern Popcorn Machine:
The "kettle" has an inner pot (which integrates the element and thermostats and an outer pot which are easy to separate with three top mounted bolts. Removing the kettle entirely from the machine makes it much easier to test.
I removed the kettle from the machine, placing it on a silicon oven mitt, and plugged it directly into the wall. The power meter here shows 5.66 amps used by the element. I used the EM100 as it is easy to see when the the element thermostat cuts power to the element. While testing, the inner and outer pot will be sitting loose, so you need to take care as there are live wires in there!! Unplug it before adjusting the thermostats! Both thermostats should open (either one of them opening will cut power to the element) once the element has reached its temperature set point. Then they will close (sending power again to the element) once the kettle temp has cooled 20-30 F.
My trusty Fluke 179 (an awesome tool!!) came with an 80BK-A thermocouple which worked well to check the temps of the kettle base. I tried an infrared temp gun which read 100 degress too cold...so I would not use one to test. It took me quite a few tries and popcorn tests to figure out that the ideal temp for the element to cut off was about 395 F (200 C) as it cools to just below 360 F (180 C) and then cycles on again. This keeps the kettle in that "magic" 360 F range for popping.
There are two thermostats on the base, which I'm guessing is for safety (vs using a thermal fuse) but they work a bit differently. One "pops" on and off with an audible click and the other has contacts which move slowly. I set the slow contact thermostat a bit higher than the "pop" version (on the right side of the pic) as I assumed that one is the safety backup. 1/4 turn will adjust about 40 F.
I should note too that if the ceramic insulators on your thermostat (there may only be one thermostat) are white, that the increase/decrease directions are opposite to what you see in my picture below.
Problem: I noticed, after a few batches on this new machine, that the popcorn was chewy and yields seemed low. Additionally, quite a few un-popped kernels were left in the kettle. The kernels looked slightly burnt and were partially split.
Solution: Kettle temperature needed to be lowered.
It took me some experimentation and reading to figure out that the kettle temperature was actually too high. The manufacturer did send me a guide to adjust but honestly, it was useless, aside from the fact that they confirmed both thermostats need to adjusted together. There was no indication of a target temp. They did advise that boiling a cup of water should take 3 minutes, but this tells you nothing if the thermostat is set too high..it just confirms the element is working. Guessing the temp is potentially dangerous as once you get into the 500 F range, an oil fire could occur. The factory setting was too hot by about 100 F. Turns out popcorn kernels like to pop around 360 F (180 C) according to some published science experiments.
How to adjust the kettle temperature thermostat on a Great Northern Popcorn Machine:
The "kettle" has an inner pot (which integrates the element and thermostats and an outer pot which are easy to separate with three top mounted bolts. Removing the kettle entirely from the machine makes it much easier to test.
I removed the kettle from the machine, placing it on a silicon oven mitt, and plugged it directly into the wall. The power meter here shows 5.66 amps used by the element. I used the EM100 as it is easy to see when the the element thermostat cuts power to the element. While testing, the inner and outer pot will be sitting loose, so you need to take care as there are live wires in there!! Unplug it before adjusting the thermostats! Both thermostats should open (either one of them opening will cut power to the element) once the element has reached its temperature set point. Then they will close (sending power again to the element) once the kettle temp has cooled 20-30 F.
My trusty Fluke 179 (an awesome tool!!) came with an 80BK-A thermocouple which worked well to check the temps of the kettle base. I tried an infrared temp gun which read 100 degress too cold...so I would not use one to test. It took me quite a few tries and popcorn tests to figure out that the ideal temp for the element to cut off was about 395 F (200 C) as it cools to just below 360 F (180 C) and then cycles on again. This keeps the kettle in that "magic" 360 F range for popping.
There are two thermostats on the base, which I'm guessing is for safety (vs using a thermal fuse) but they work a bit differently. One "pops" on and off with an audible click and the other has contacts which move slowly. I set the slow contact thermostat a bit higher than the "pop" version (on the right side of the pic) as I assumed that one is the safety backup. 1/4 turn will adjust about 40 F.
I should note too that if the ceramic insulators on your thermostat (there may only be one thermostat) are white, that the increase/decrease directions are opposite to what you see in my picture below.
At least it was for a rewarding purpose.
