The maltose in the grist dissolves in the water and the remaining sweet liquid, called wort, is drained out of the mash tun. After cooling, the wort is ready for fermentation.
A mash tun is a brewing vessel made of cast iron or stainless steel, wherein the grist is mixed with warm water. The bottom is a sieve which can be opened and closed. Once opened the liquid can flow into the underback, while the solids stay in the mash tun.
The container that catches the wort when the sieve in the mash tun is opened is called the underback. It catches the liquid before it is pumped to a washback.
Mashing takes lots of water. It is done in two or three cycles, depending on the preferences of the distiller; the water temperature may differ at each cycle. The quality of the water and the substances found in it are very important during this phase. Too many minerals, like copper or iron, could cause problems during fermentation, which is the next step in the process. The acidity of the water is also important and affects the forming of esters (chemical compounds) during fermentation.
This is an edited feature provided by SMWS ambassador Hans Offringa from his comprehensive A Field Guide to Whisky: An expert compendium to take your passion and knowledge to the next level which you can purchase by clicking on the link.