So far, we've talked a lot about how to distill, but not much about what to distill, that is, what alcohol-containing wash or mash do we put in our still to concentrate ethanol and extract flavors. What you will put in your still is a wash, a beer or a wine. At its simplest, they are the same thing, a mixture of fermentable sugars and other stuff, that has been fermented by live yeast to create ethanol, drinking alcohol.

A wash (sometimes called a "mash") can be almost any fermented thing. A beer is fermented grain sugars, and a wine is fermented fruit sugars. Vodka is often just fermented table-sugar water.

That "other" stuff hopefully includes nutrients for the yeast, because yeast does not live by sugar alone, and also other compounds that will give the distilled spirit flavor.

Basically, there are two kinds of materials you can use to make alcoholic washes, sugar-bearing materials, and starch-bearing materials.

Sugar-bearing Materials to Ferment for Washes

Any material that contains fermentable sugars, including simple table sugar, sucrose, can be used to make a solution that can be fermented to produce alcohol that may be concentrated by distilling.

The two most commonly-used sugar-bearing materials are fruits and sugar-industry products, ranging from refined sugar through cane juice and brown sugar to molasses.

Liquors distilled from fruit sugar fermentations are usually called "brandies", and liquors made from sugar cane products are usually called "rums".

Using Starch-bearing Materials to Make a Wash Fermentation

To use a starch-bearing material to make liquor, you must first convert the starch to fermentable sugars, which is the only food yeast can eat.

Chemicals called amylase enzymes can convert starches to fermentable sugars. Amylase enzymes are produced in grains by a process called "malting". Most malted grains contain enough enzymes to convert all the starches in the grain to fermentable sugars. In addition to malt enzymes, a variety of amylase enzymes may be purchased at homebrew supply stores.

Note that while malted grain contains amylase enzymes, it also contains most of its original starch, which is still unavailable as yeast food. Malted grain must be specially treated to use its enzymes to convert its starches.

After grains, the most common starch-bearing materials for making liquor are root vegetables like potato and sweet potato. Purchased enzymes or malt enzymes must be used to convert potato starch, although sweet potato does contain amylase enzymes.

Shortcuts to Grain Washes

Because starch conversion is far more complicated and involved than simply using already-available sugars, distillers have looked for shortcuts to simplify making grain whiskey.

Converting starches in grain to fermentable sugars is called "mashing", or creating a "mash" (sometimes called a "thick mash"), but if a simple sugar wash is flavored with unconverted grain (which also provides yeast nutrients) the result is callled a "thin mash". Because thin mashes are way easier to do than a proper grain mash, they have become a popular way for hobbyist distillers to make grain whiskey.

Uncle Jesse's Simple Sour Mash (UJSSM) whiskey recipe has become popular for that reason.