The process of distillation gets a lot of the attention when it comes to crafting great spirits, and rightly so. In reality, however, by the time a grain mash or wash is ready for distillation, the stage has already been set—and that starts with the process of mashing or cooking.
Turning Food for Plants into Food for Yeast
The ultimate goal of mashing and cooking grain for whiskey and other spirits—as well as for beer—is to create food for yeast so that it creates alcohol.
Grains such as barley, wheat, rye, and corn are full of long chains of starches, which are energy stored by the kernels so that they can germinate and grow into new plants. That type of chain is known in chemistry as a polymer. It is a long, repeating strand of molecules and chemical bonds designed to efficiently store and safeguard energy until, in the case of grain, the seed uses its built-in biochemical tools to access that energy and tap into it for growth.
Before grain can be fermented to any significant degree, so that it can be distilled, the distiller first needs to unlock those starches in a mash tun or mash cooker. The first essential step of cooking is to gelatinize the grain starches. The gelatinization process makes the starches available for further processing, which includes breaking them down, converting them, into their more easily fermentable constituent sugars.
Broadly, barley and wheat have relatively lower gelatinization temperatures that are similar to the ranges in which their starches break down. However, other grains—such as corn and rye, used for bourbon, rye, and other spirits—require an additional step to access the grain starches. Rye has a gelatinization temperature of up to about 160°F (71°C)—depending on variety and other subtle variations in grain composition—while corn’s requirement can be up to 165°F (74°C).
Commonly, a distiller will cook corn or a mash containing corn at 180°F (82°C) or higher for an hour, to swell and gelatinize its starches. Anyone who has stood at the stove stirring a pot of grits or polenta for an hour has experienced this phenomenon: Bland and starchy at first, the corn eventually turns sweet as the starches gelatinize, indicating that the dish is nearly finished. Some larger commercial operations will even pressure-cook their grain at temperatures above 212°F (100°C) to reduce time or improve extraction. (Distillers often use enzymes to aid the process in both the gelatinization and saccharification stages.)
In practice, a gelatinization step is generally required in grain-on spirit cooks but not for spirits that have the grains separated out. Mashes for spirit types that rely on high levels of corn and rye—bourbon, rye, corn whiskey—more closely resemble oatmeal or porridge, compared to the identifiable particulate of a malt mash. As a result, these spirits are usually produced in a cooker, whereas a malt-whiskey mash—or potentially even a wheat-heavy mash, using enough filtration aids—can be produced in a mash tun, which can separate the liquid from the grain solids during runoff. (However, the mosaic of approaches adopted by craft distillers makes any categorical statement here impossible.)
When using a mash cooker, the grain goes into the vessel either all at once or in stages, depending on the processing temperatures needed. The distiller blends the grain with water as it enters the vessel, resting at the appropriate temperatures for a given mash type and the distiller’s enzyme choices.
In lieu of using raw grains and incorporating a gelatinization stage, a distiller can also use malted grains. While these have slightly different flavor profiles—which may or may not be what an individual distiller is looking for—the malting process incorporates gelatinization, which takes some of the burden of processing out of the distiller’s hands.
Accessing the Sugars
Gelatinization doesn’t fully break down the grain’s starch molecules into fermentable sugars, but it opens the door for the second stage of corn- and rye-based spirits: saccharification. (In barley and wheat, whether malted or raw, a lower gelatinization temperature allows that process to occur simultaneously with saccharification.)
Grain starches consist primarily of amylose, which is a straight chain of glucose molecules—also known as 1,4 bonds—with some branched amylopectin, or 1,6 links. Saccharification breaks those chains down through the use of enzymes, either resident in malted barley or added (i.e., exogenous) by the distiller.
The primary enzymes upon which a distiller relies are alpha amylase, beta amylase, and glucoamylase; when properly applied, they’ll break those chains of grain-borne sugar molecules down primarily into single (glucose) molecules, two-molecule maltose sugars, and three-molecule maltotriose sugars. The temperatures at which these enzymes denature and become ineffective is lower than the gelatinization temperature, so the distiller must cool the mash to saccharification temperature—which varies depending on the enzymes added—after any gelatinization rest.
Rests generally involve:
- a high-temperature gelatinization stage, with the possible addition of a high-temperature enzyme;
- cooling the mash to saccharification temperature, with the possible addition of enzymes and/or additional grains such as malted barley and wheat;
- a saccharification rest; and
- a final cooling.
Grain on, Grain off
When distillers use a mash cooker, they’ll generally distill the spirits on-grain. That is, after fermentation, the entire mash—including grain, yeast, liquid, and all—goes into the still for distillation. All other things being equal, these distillations result in heavier, richer spirits because of the higher proportion of residual oils and other heavier volatiles that remain in the grain solids.
However, for malt whiskeys and similar grain-off spirits, the distiller first separates the grain solids from the liquid portion using a mash tun or lauter tun. Producing a malt whiskey wash is a process familiar to brewers, who mix malt and hot liquor (water) together in a mash tun. After a saccharification rest—also known in brewing as a conversion rest—the brewer separates or filters the mash liquid from the solids via a false bottom in the mash tun or a separate lauter tun, then runs off to either a fermentor or a boil kettle.
When the wort is separated from the grains via a mash tun or mash/lauter system—with only the liquid making its way to fermentation—it will obviously be distilled off-grain. That allows the distiller to ferment and distill the sugary runoff, making transfers and cleaning easier while also resulting in a less heavy, grain-forward spirit, all other factors being equal.
Through gelatinization and saccharification of the grains, the cooking or mashing process—with all its controllable variables—starts setting the stage for the distillation. Then the real fun begins.