A mash tun is a container you boil the grains in to make a all grain or partial mash beer. You have to heat the grains to certain temps and hold those temps for 90 min. or so to extract the starches from the grain. Those starches get changed into fermentable sugars by the amylase in the kernels if grain. The yeast changes those sugars into alcohol and carbon dioxide (as a byproduct) to make beer and the alcohol in it. I need a controller that works better than the burner on my stove.