First of all the barley is filled into tanks known as steeps where it is soaked with water for 48-72 hours to start a process called germination. Since grains are very hard they need to be softened give access to the sugars inside.
Traditionally the soaked barley is then spread out across the malting floor to continue germinating for 5-10 days and to extract moisture from the soaked malt.
Because the temperature is higher in the bottom layers, germination proceeds faster and it needs to be turned over. In times before machinery was available, the workers turned it over by hand with so called shiels, big wooden shovels, which was, and still is, a very labour heavy job. Nowadays most distilleries don’t malt their barley on site anymore and the malting companies use machines for the process.
During its time on the malting floor the barley seeds start releasing starch, a long chain sugar or polysaccharid. This happens with the help of two enzymes, cytase and diastese, that are released when the seed comes in contact with water. Cytase breaks down the cell walls that hold the starch, while diastese is responsible for the conversion of starch into soluble starch and eventually into sugar.
Eventually the barley seeds start sprouting and is now called green malt. This is when the barley has to be dried to stop it from growing and prevent it from using up all the sugars that are needed for fermentation later.
To dry the now sprouting barley and stop it from continuing its growth process, the green malt is transferred over to a drying or kilning floor.
The malted barley is spread out on a perforated floor with a coal fire underneath. Temperatures of 70°C or higher destroy the enzymes responsible for the sugar conversion so the hot air rising up stops it from germinating further while moisture level of the malted barley drops from 50-45% to less than 5%.
While kilning distilleries can add peat to the fire. Peat is partially decayed organic material that has piled up for thousands of years in the ground of wet environments such as bogs and fens.
Peat smoke contains chemicals called phenols which attach to the wet barley when passing through it. This results in a smoky aroma and flavour that is carried through the whole production process and into your whisky.
How much of those flavours will remain depends on how much peat is added to the fire, how long the barley is exposed to the peat smoke and what type of peat is used. The amount of phenols in the malt is measured in PPM (phenol parts per million). Usually the measurement is performed right after the malt is dried and that is the number that distilleries account to their products. In fact during the process only one third of the phenols of the peated malt will eventually end up in the final liquid. The rest vanishes during mashing, fermentation and distillation as well as maturation.