This is a terrible idea. Back in the day, I'd service peoples' PCs, and inevitably a certain % were smokers and that tar buildup was bad enough, but the fumes from coffee coat everything nearby, probably over 10X faster than tobacco smoke.
You could try to seal the chamber it's in but inevitably if you can smell the coffee, some of that is going to be sucked back in unless the system is passively cooled.
I noticed the article stated that it intakes in the rear then out the front of the case, but that still doesn't make it a good idea unless you're just throwing together old salvaged parts for the novelty of it instead of modern parts worth some money and worthy of being used on a regular basis.
All this to be able to make a single cup of coffee? The effort:reward ratio is terribly low. This project was about creating youtube content.