Islay whisky making

Distilling on Islay Malting

In order to create whisky, we need something we can turn into alcohol. Single malt whisky’s base ingredient is barley: readily available, relatively inexpensive and packed with the precursors of sugars that can be converted into alcohol during the whisky making process. The first step in making whisky is unlocking that sugar.

The vast majority of a grain of barley is made up of the endosperm – starchy tissue that fuels the growth of the grain into a plant. This is our source of sugar, but it cannot be directly turned into alcohol. It must first be converted into different forms of sugar, including maltose and glucose. This is part of a process called malting.

In its simplest form, malting is the tricking of barley into beginning the process of germination – the growing of a seed into a plant. This starts the conversion of starch into a form the plant can use to grow and which we can turn into alcohol. This process is halted, leaving a grain that contains useable sugar. This is malted barley.

  • FACT

    2 distilleries on Islay use barley grown on the island
  • FACT

    3 distilleries on Islay have malting floors
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The first step is to hydrate the grain, which has the dual purpose of initiating germination and preparing the starch in the endosperm for conversion. This is done by alternately soaking the barley in water and air-resting in a process known as steeping. The resting is equally as important as the soaking, allowing the barley to absorb surface moisture, take in oxygen and expel carbon dioxide, as well dissipate the heat created during respiration.

The barley will start with a moisture level of around 12%, having been dried for storage. Steeping will quickly raise the moisture level to more than 30%, and further cycles are used to bring it up around 45%. The steeping process can take between 48 and 72 hours.

In addition to hydrating the endosperm, steeping also removes abscisic acid (ABA), a hormone that stops germination by preventing the formation of enzymes in the aleurone layer of the endosperm. When the levels of ABA in the grain drop to a low enough level, enzyme production will cause germination to begin.

Traditionally, the grain would now be laid out on a malting floor to allow germination to convert the starch to fermentable sugars, but more modern processes now use large vessels to store the grain. The idea is the same, and the malt is regularly turned to allow air circulation while germination occurs. Conditions are carefully managed to ensure the grain does not dry out or get too hot or cold. Depending on conditions and the desired malt character, germination will continue for between four and six days.

During germination, enzymes are produced in the aleurone layer. The most important actions of the enzymes at this point are to dissolve cell walls in the endosperm to reveal the starch, break up the tightly packed starch granules and then convert them into fermentable sugars.

Once the required level of conversion and enzyme production has occurred, the grain is known as green barley. The malt can be used at this point, but in most cases the germination process is stopped by applying heat – this is known as kilning.

While open fires were once used to heat kilns, most facilities now use hot air. The use of peat fires to dry barley created the most iconic flavour of Scotch whisky – peat smoke – but these days, peat is used to infuse flavour into the drying grains rather than as a major source of heat. Kilning itself also produces a range of compounds that are important for the formation of flavour during fermentation, distillation and ageing through a variety of processes, including the Maillard reaction.

The evaporation of moisture from the barley will initially keep the grain bed below the temperature of the hot air being used to dry it. This continues until the malt contains about 20% moisture, at which point the temperature quickly rises. Conversion and enzyme production continue until this point, but enzyme activity will lost as temperatures rise. These enzymes are not only essential to the conversion process but also assist in germination, so care is taken to reduce the losses by controlling the temperature of the drying air.

The grain is dried to about 5% moisture, at which point the malt is ready to be stored prior to use.

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