Lately I’ve been really intrigued with the concept of spunding valves. A spunding valve is like an air regulator that you attach to the gas port on a closed fermentation vessel. It is generally adjustable and you can dial in the point at which it will release the excess co2 to the air. Something like a spunding valve is necessary in order to do pressurized fermentation.
OK, but why?
Brewers use these during secondary or the end of primary to carbonate the beer while it is finishing. It has the benefit of skipping (or combining) the force carb step, and that means that you can go grain to glass faster!
There are a few different ways to build one of these. Here is an article from BYO, here is a post from homebrewtalk, and here is a ready to buy version from morebeer. All of those cost around or a little over $30.