Traditionally, peat is burned to dry out barley which has been wetted to make it start germinating. When barley germinates, it changes the complex sugars into simple sugars that can be used by the plant to grow. The germination process needs to stop, otherwise the barley grains will end up as barley plants. Peat is burned to heat up and dry out the barley grains, which retains the simple sugars,and halts the growth of the barley. These simple sugars are called malts, and the process is called malting and from fermenting these sugars and distilling them, whisky is made.
The flavours imparted into the whisky in this process are left over from the smoke that permeates the barley grains. The flavours maybe from peat or from the burning of the peat which is referred to as smoke. These flavours are distinctly different, but often occur together. The smoke flavour is like the smoke you will smell on a cold winters night, when people have their fire places lit, or a good old camp fire, wood fired bbq, or pizza oven. It can also be thought of in terms of smoked meats, so you will often hear of smokey whiskies having bacon type flavours.
Peat can be found independently of smoke when the water used for the whisky comes from a spring that has come through peat. It is most usually found alongside smoke flavours rather than in isolation (as very few – if any – distilleries still use natural spring water). Peat smells like fresh compost, or rotten vegetables, but more pleasant. Often described as an ‘earthy’ flavour – it can be an acquired taste and like many acquired taste it is loved by it fans, and often misunderstood by it’s detractors.