What is a “Thumper” ?
A “thumper” is an extra chamber sometimes fitted to a pot still. It can be as simple as a glass jar with two holes in the lid. The off-take from the still is fed into it, with the pipe running almost all the way to the bottom of the jar; the jar is half filled with liquid (water or mash or tails) so that the vapour from the still will bubble up through it; then the vapour coming off it is collected & cooled as per normal. It acts as a second distilling chamber using just the heat from the vapour, and lifts the purity from 50-60% to 70-80%, hence improving what might otherwise be a very mediocre design. Don’t make the thumper too small, and start it off with liquid already high in alcohol.