(n.) A mixture of grains and water heated to encourage the extraction of grains’ fermentable sugars. Cereal grains, including barley, corn, rye and wheat, contain complex carbohydrates that can be converted into sugar that yeast can consume, leaving a byproduct of alcohol and carbon dioxide.
To create a mash, the grain bill (the combination of cereal grains) is usually lightly milled to remove the husk from the seed, which allows better access to the grains’ starch. The milled grain is then poured into warm water, and kept warm until the grains’ sugars are released. The mixture is usually then reheated to almost boiling, then strained. The strained liquid will then contain enough sugars for fermentation to take place.
In the production of bourbon and Tennessee whiskey, the term “sour mash” is used to indicate that some of the distilled mash from a previous batch is added to the current batch, which helps to protect the mix from bacteria and add a distinctive flavor. Some producers, notably Woodford Reserve, have recently introduced a sweet mash line, which skips this step.