In brewing and distilling, mashing is the process of combining a mix of ground grains – typically malted barley with supplementary grains such as corn, sorghum, rye, or wheat – known as the "grain bill" with water and then heating the mixture. Mashing allows the enzymes in the malt (primarily, α-amylase and β-amylase) to break down the starch in the grain into sugars, typically maltose to create a malty liquid called wort.

The two main methods of mashing are infusion mashing, in which the grains are heated in one vessel, and decoction mashing, in which a proportion of the grains are boiled and then returned to the mash, raising the temperature.

Mashing involves pauses at certain temperatures (notably 45–62–73 °C or 113–144–163 °F) and takes place in a "mash tun" – an insulated brewing vessel with a false bottom.