[This is republished from an article I wrote for Make: magazine]
I love cold brew coffee. Its rich and delicious flavor, and low acidity, means it tastes great over ice. Traditional hot-brewed coffee methods simply can’t compare; when chilled and served on ice they tend to taste diluted and acidic. I have a small commercial drip tower that works very well, however, given the fact that cold brew takes up to 18 hours to brew, it’s disappointing to finish it off in just a few drinks. You can buy large cold-brew towers, but they’re very expensive, aimed at coffee shops. I decided to build a much larger brewing tower from scratch, and to make it considerably higher precision while I was at it — drip rate is everything when it comes to cold brew — using a microcontroller-driven solenoid valve for exact drip rate.
A cold-brew coffee tower consists of three main parts: a water receptacle at the top with a drip control valve, a chamber for grounds in the middle where the brewing takes place, and a carafe to receive the brewed coffee at the bottom.
Sourcing parts was a bit of an adventure. I had planned to use chemistry lab glass for all three systems, but eventually realized that this would be either too expensive, in the case of using a separatory funnel for the tapped water receptacle, or impractical — a Buchner funnel large enough to hold 150 grams of ground coffee would be much too squat and wide to saturate evenly. After much hunting I found the ideal components: a water serving pitcher for the top receptacle, a siphon brewing upper beaker as the grounds chamber, and a flat-bottomed boiling flask as the receiving vessel. For a bit of spiraling glass laboratory aesthetic I added a Graham condenser to the mix, purely for looks.