From malt to whisky

The term “whisky” refers to any alcohol distilled from fermented grains, whether or not the grain is malted. There are many kinds of whiskies and many origins:  Scotch and Irish (Since  the 11th century),  the New World  American whiskies like Bourbon,Tennessee and Canadians, and more recently Japanese and Chinese whiskies.

In the United States “malt whisky” must be produced from fermented wort including no less than 51% malted barley and aged in new charred oak barrels.

If this whisky is aged at least two years, contains no additives for taste or colour and has not been mixed with neutral alcohols or other types of whisky, it can legally be called “straight malt whisky.” If a whisky is not straight malt but contains at least 51% straight malt whisky, it must be called “blended malt whisky.”

The role of malt in the production of whisky

Barley malt is used in three parts of the whisky  process:  making yeast media, pre-malting and the cooking process itself.  Malt is cooked with rye to create a sugar rich environment in which yeast is propagated in order to convert  sugar to alcohol ; before introducing corn and rye into the cooking process a malt “slicker” or pre-malt is added to reduce the viscosity of the slurry and reduce the chance for doughballs; and, finally, after the corn and rye have been added and cooked at 212°F to liquefy the starch in those grains the remaining malt is added. Alpha amylase and beta amylase enzymes that are created during the malting process are introduced into the slurry at no higher than 152°F.

Alpha amylase converts starches into about 80% maltose and 20% dextrins.  After the cooking process distillers yeast is introduced into the mash and converts sugars into alcohol which reduces the sugar content.  At a certain point in the fermentation process the beta amylase enzyme, which is still active in the mash, initiates a secondary conversion of starches into sugars which increases the alcohol yield. 

Other raw material than malt used to produce Whisky malt

Ingredients in the production of whisky are corn, rye (or wheat), barley malt, water, backset stillage (which is fermented mash after distillation which helps in adjusting the pH of the cook) and yeast.

As a rule, distillers use 8-12% of barley malt in their mash bills (percentage of the different grains used) based on yield, experience and preferred mash bills.

Malt’s role in distillation

By the point of distillation malt has already accomplished its mission of converting the starches from selected grains into various sugars (maltose, dextrose, fructose, and glucose).  Yeast is then added that acts as a catalyst in converting these sugars into alcohol.

During fermentation yeast breaks down the sugars created by the malt and this chemical reaction creates alcohol, carbon dioxide gas and heat.  The alcohol is eventually separated from the mash (now called a beer because it contains 9-11% alcohol by volume) via distillation, the carbon dioxide is vented into the atmosphere and the heat is controlled below 90°F during fermentation using cooling coils.  If temperatures rise above 90°F the yeast will stress and die resulting in a poor yield and possible quality issues.

What malt does for whisky

Whisky flavours come from a multitude of sources: the water used, mash bill (percentage of corn, rye, wheat and barley malt used in the mash), the distillery yeast used, the cooking and fermenting processes, the type of stills used (column versus pot), barrel specifics, length of aging and final processing.

Barley malt’s main job is  the conversion process but it also adds various flavours depending on the malting process and the combination of the flavour sources mentioned above.  Some of the noticeable characteristics are:  earthiness, cereal, nutty, grainy, honey, and oakness.

The different types of malts used by distillers

Typically there are two types - natural barley malt and gibberellic acid malt. The “gibb” malt increases the amount of alpha amylase in the barley and is used by most bourbon whisky producers.  As interest in different whisky flavours has increased, distillers have looked toward flavoured malts (caramel, peat, cherry, etc.) to create new products for the whisky aficionados.

Providing malt for the distillers

Distillers look for malts with high diastatic power of the alpha and beta amylases enzymes, and Malteurop focuses its efforts on providing them.  This is because the primary purpose of barley malt for the distiller is to maximize conversions of starches to sugars and thus maximize the alcohol yield of a bushel of grain.  A general range of 5.0 – 5.3 proof gallons can be produced from a bushel of grain (56 pounds). A secondary consideration, but an important one, is the flavouring component from the malt itself.