I know you need heat for cornstarch to thicken. When heated in the presence of water the molecules absorb the water, swell, and burst releasing more molecules. Since starch molecules are large all these loose molecules floating around become entangled with each other, forming a web, and thickening whatever.
Temps below around 185 °F might not be high enough, depends on the quality of the starch, and temps over 212 °F can break the web.
You nailed it.
I never noticed in the video where he transferred the pot from a counter onto (I'm guessing) an induction stove. And knowing that, I noticed a wisp of smoke.
I thought he was mixing the ingredients in a pot just because that's what he had.
According to my cheap infrared, it started to thicken around 160 F.
Wish me luck.
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And yes, I see what I did there.
I didn't tuck the last disk under the first one I started with. Duh.