The mild, light character of grain whisky greatly contributes to the flavor balance of blended whisky. Blending with malt whisky softens the strong character of malt whisky to produce a pleasant-tasting spirit that goes down smoothly.
Like malt whisky, grain whisky is also produced through a process of mashing, fermentation, distillation and aging. It differs significantly from malt whisky production in that corn is used as the main ingredient and distillation occurs in a continuous still. In addition, prior to mashing, a process called “cooking” is required.
The main ingredient is corn. A part of the process uses malt as a source of enzymes. Presently, in Scotland wheat or a combination of wheat and corn is used as main ingredients. Malt is used because even if corn is germinated, it does not produce a large amount of diastatic enzymes. The malt serves to saccharify the starch in the corn without germination.
In the case of malt whisky, malting breaks down starch cells in the germinating malt, making it easier to mash (saccharify). By contrast, grain whisky uses un-germinated corn, making it necessary to break down the starch cells by other means. Cooking is the process that does this. The selected corn is first ground as finely as possible. Water is added to the ground corn, and the starch cells are broken down by exposing it to high-temperature, high-pressure conditions. Once the cooking is completed, the liquid is cooled before advancing to the mashing process.
Mashing is performed by adding a gruel-like solution of milled malt and process water to the cooked liquid. This is when the diastatic enzymes in the malt go to work. The corn starch is broken down into sugars and a sweet liquid, or mash, is created.
Fermentation Once the mash is cooked, yeast is added and the mash is fermented in the washback. This process takes slightly longer than fermentation for malt whisky, which could take up to 96 hours. The resulting liquid, called wash, is around 10 percent alcohol.
A continuous still is used to distill grain whisky continuously at an alcohol content below of 94.8 percent. If the alcohol content climbs to 95 percent or higher, then it will lose its gain character thus becoming a neutral spirit like vodka.
A continuous still is usually made up of two to four columns, and inside each column are several dozen shelves. Each shelf serves like a single pot still. The wash continuously flows from top to bottom, and the vapor continuously flows from bottom to top. The higher it rises, the greater the alcohol content in the vapor, and the lower it descends, the lower alcohol content in the solution. Compared to a pot still, a continuous still can produce spirit that has higher alcohol content, but the style of the resulting whisky will be gentler in character. Grain whisky, therefore, is called the silent spirit, in contrast to the loud spirit, malt whisky.
Just like malt whisky, grain whisky is also matured in a cask. While oak casks are the most commonly used, the casks that have been used a few times in the maturation of malt whisky are preferred. This gives a mild cask flavor to the grain whisky. Since grain whisky is distinguished by a flavor that is cleaner than that of malt whisky, it is best to use older casks that do not release cask compounds in large amounts.
連續式蒸餾器通常由兩至四個柱餾塔組成，每個柱餾塔中有數十個格層。每一格都像一個壺式蒸餾器，麥酒汁從上到下不斷地流動，蒸汽則從底部向上升。位處越高的蒸氣，所含的酒精也越高；愈往下走，液體中的酒精含量則越低。與壺式蒸餾器相比，連續式蒸餾器能生產出酒精含量較高的烈酒，造就出偏向溫和的風格。 因此，穀物威士忌也被稱為Silent Spirit，與Loud Spirit麥芽威士忌相映成趣。