A YouTube video by Sweet Maria's TLDR: What do you think this is caused from?

Tom brought up a point that I've always noticed, come up with some guesses, and mostly just pondered on. With trying to learn my machine and how to roast so far my best guess is that the coffee becomes cloudy when the bean structure is not broken down enough. I've come to this conclusion because come from the air roasting, for me it's easier to get a cloudier (but still developed) almost spongy looking grounds. (When looking at the grounds steeping in my aeropress.) When I roast darker it becomes as "glassy" as coffee's bought from drum roasters. But I am not good at getting a very brittle/glassy light roast.

TLDW? The video shows that fresh brewed coffee is clear when it's hot and gets more opaque as it cools.

Oh good point, when I watched this (early in the morning) I thought I was two separate roasts. What I'm more concerned with was what I noticed during brewing a sample, where the grounds in the water look more "spongy" than "glassy". Usually seen going from lighter to darker roasts. Have you ever noticed this?

To answer Tom's question, it's probably the flavonoids and other plant chemicals that would change opacity based on temp.

Like chill haze in beer where protiens and flavonoids form bonds as it cools.

Black tea does this as well; more if it's hot brewed. Cold brew seems to be immune. An interesting experiment would be to reheat it and see if it clears up, like it does with tea.