Malt is essentially barley which has been allowed to germinate by soaking in
water then has been dried by the application of heat. The malting process
converts the stored starch into soluble compounds such as the sugar
maltose and by so doing makes fermentation possible. Drying the malt over a
furnace stops the germinating process and lacing the furnace with peat imparts
a peaty aroma to the malt.
It is worth noting that until about the 1950s all malt distilleries would
carry out the entire process on the site - malting, fermenting and distilling.
Now only a few distilleries have their own maltings.