Water is needed in all stages of the production of whisky. It is mixed with the barley to promote germination, it is added to ground barley grist to create a mash and it is required for diluting most whisky before maturation and once again before bottling.

Barley, water and yeast are the exclusive ingredients required in the production of single malt Scotch.

The barley used to make the whisky is "malted" by soaking the grain in water for 2-3 days and then allowing it to germinate to produce the necessary enzymes required.
The malt is milled into coarse flour, and mixed with hot water to activate the enzymes, which leads to conversion of starches to fermentable sugars. Long starch chains are broken into glucose, maltriose, and maltose, which can be fermented by yeast.

The extraction is carried out in a large kettle called a mash tun. At first, the hot water activates the enzymes by providing an optimal temperature for activity in the grist. The enzymes act on the starch to convert it into sugar, and in the process it produces a sugary liquid, known as wort.

Yeast is then added to the wort for fermentation, in a large vessel called a washback. Washbacks are commonly made of Oregon Pine or stainless steel. The yeast feeds on the sugars and as a by-product produces both carbon dioxide and alcohol; this process is called fermentation and can take up to three days to complete. When the process is complete, the liquid contains an alcohol percentage of 5% to 7% by volume, and is now known as wash.

To be called a single malt Scotch, a bottle may only contain whisky distilled from malted barley produced at a single . If the bottle is the product of single malt whiskies produced at more than one distillery, the whisky is called a vatted malt, or a blended malt. If the single malt is mixed with grain whisky, the result is a blended .

The age mentioned on a bottle of single malt Scotch is the age of the youngest malt in the mix, as commonly the whiskies of several years are mixed together in a vat to create a more consistent drink.