Credit for this post goes to Kyle Watson, better known as Mr. Crampy to biking enthusiasts around Redmond. Over a steaming cup of double-Catcher Koke this morning, Mr. Crampy drew on his physics background to explain how the double Coffee Catcher brewing works.
Pulling the first Coffee Catcher creates a vacuum beneath the rising Coffee Catcher. The vacuum isn't perfect of course, but Mr. Crampy thinks it's sufficient to generate an efficient dispersion effect, completely mixing the coffee and grounds to produce a very even extraction. He suggests this even extraction is the reason for the coffee's particularly clean taste.
This is by far the most reasonable explanation I've heard for the phenomenon. While convinced this method tastes great, I'd been stumped as to how extraction worked properly with the coffee locked away for 3/4 of the brew time. Perhaps the agitation and negative pressure Mr. Crampy alludes to accelerates the brew during the final minute.
Here's a movie of the process. Other double Catcher videos over here.