A mash tun is a vessel used in the brewing process to convert starches from grains into fermentable sugars. It typically holds crushed grains, known as the mash, and hot water. The heat activates enzymes in the grains, which break down the starches into sugars, creating a sweet liquid called wort. After the mashing process, the wort is separated from the solid grain husks. This liquid is then transferred to a boil kettle for further processing, where hops may be added. The mash tun is essential for producing beer, as it directly influences the flavor and alcohol content of the final product.