Hi there,
I've been making cold drip during the Summers with the same basic rig as many others I've been reading about...
A Separatory Funnel and an Aeropress to hold the grinds
I recently swapped the aeropress for a vietnamese coffee press for the reduced height, but it's a bit wider in the middle, which got me wondering...

does the diameter of the grind holder make a difference. To take it to an extreme, I would think that if you had a vessel that was a foot long in diameter and a giant filter paper covering the whole thing, it would still be hard to have an even extraction across all the grinds with water dripping on one spot. I (and I assume many people) used an aeropress because I had one lying around, I had the paper filters which were the perfect size, and it matched the shape of the fancy setups that you could buy. But if I had a holder that was smaller in diameter, would that make a significant difference? Or as long as the grounds stay wet, am I getting a pretty even distribution?

I'm not willing to invest in a chromatography column to test this, but after looking at some internet videos about BHO extraction, I figured I could try with a turkey baster plugged with cotton. I'm about 2 days out from brewing my next batch, but until then, I wanted to see if anyone had any thoughts about it. I tried searching, but couldn't find much discussion about this particular variable.

Interesting question, regarding the Aeropress size, the Bruer uses the same size and filter for their cold brewer. Putting a filter on top of the grounds helps distribute the water, I also do a hot bloom and stir before the cold drip.

In hot coffee brewing bed depth plays a big role and using the right filter holder size sets the bed depth.

So I tried setting up an Oxo turkey baster that has an inside diameter of just under an inch in my drip system. I could only fit 15g of medium ground beans in there. With that amount, the coffee grounds took up a column height of 9 inches, which was pretty close to the entire height of the baster. I plugged the bottom with cotton.



Anyway, I think I used too much cotton, and the eluting took too long. I couldn't get the drip to go slow enough to match the rate at which coffee was coming out. I could try again with less cotton, but that's too hard of a variable to control. When I have some time, I'll put a mesh on the tip, and try to control the rate of flow through the grind size.

Also, there's the obvious limitation of how much can be made at a time when you can only fit 15g in there.