Mash is a term used in the whiskey industry to mean a blend of hot water, yeast, and grain meal that undergoes initial fermentation to produce alcoholic beverages. Additionally, sour mash refers to how distillers utilize the mash from the previous batch to initiate fermentation in a fresh batch and with frequent application in the production of bourbon and Tennessee whiskey. Contrary to using already used mash, the sweet mash adds fresh yeast in a new batch to initiate fermentation.