Single malt Scotch whisky is Scotland's original whisky. It was traditionally made in the Highlands in the 18th and 19th century only from malted barley. In contrast, Lowland whisky was often made from other grains including oats, wheat, and later maize (corn). Until the Excise Act of 1823, much single malt Scotch whisky would have been made and sold illegally. The passing of this act paved the way for the commercialisation of the industry when famed illicit distilleries like George Smith's Glenlivet went legal.
This led to a boom in distillery building that continued until the 1890s. A series of regions emerged which produced whiskies in a distinct style: Islay, Island, Speyside (previously known as Glenlivet), Campbeltown, Highland and Lowland. Much of this character came from the fuel used for malting the barley. In the case of Islay, it would have been the island's plentiful peat, resulting in a smoky, medicinal taste, whereas Speyside's good railway connections would see it adopting anthracite, a kind of smokeless coal.
By the 1870s, however, most Scotch whisky for export would have been a blend of characterful Highland single malts and Lowland grains. These were pioneered, aged and marketed by shopkeepers like John Walker of Kilmarnock, Chivas Bros of Aberdeen and Arthur Bell & Sons of Perth. These merchants also imported rum, Port, sherry, Madeira and other wines, and had discovered that single malt Scotch whisky did something extraordinary when aged in seasoned wood. In whisky's illicit years, it would have been drunk unaged or even flavoured with herbs and spices but eventually whisky came to be generally regarded as an aged product. Since a court ruling of 1909, Scotch whisky, both malt and grain, has to be aged for a minimum for three years.
Now to be labelled as a single malt Scotch whisky, the spirit has to be made only from malted barley, batch-distilled in copper pot stills (usually twice though there are some triple-distilled single malt Scotch whiskies), aged for a minimum of three years in oak casks in Scotland, and bottled at no less than 40% ABV. The industry is governed by the Scotch Whisky Association (SWA). Within these strict parameters, however, each distillery produces a unique style through differences in fermentation techniques, distillation, wood ageing etc. On the whole, the regional styles like Islay or Speyside owe more to tradition than anything intrinsic to where they are made.
While for much of the 20th century, Scotch whisky drinkers would have drunk blends, often mixed with soda water, single malts were highly prized by aficionados, though usually only seen as independent bottling from merchants like Gordon & MacPhail of Elgin. In the 1960s, however, Glenfiddich in Speyside began bottling and marketing its single malt Scotch whisky internationally. Its success led to others making this leap such as Glenfarclas, Macallan and Glenlivet. Single malt Scotch whisky as we know it had arrived.
Many of the distilleries built during the boom years of the 19th century have since closed down but in the 21st century Scotch whisky grew rapidly once more and there are now more than 130 malt distilleries in operation. These range from tiny farm operations to vast factories of whisky. Despite the global fame of single malt Scotch whisky, however, the majority of production is still used for blends which make up around 85% of global sales. The success of single malt Scotch whisky has inspired distillers all over the world with countries such as Taiwan, Japan, Australia and America all making single malts that, while distinctive, owe much to the original.
In the 19th century, characterful malt whiskies would have often been drunk mixed with hot water, honey and spices in the form of toddies. Nowadays, most are drunk neat or with a little water but we're starting to see a return to mixing with certain malt whisky cocktails like the Smokey Cokey, a blend of Lagavulin and Coca-Cola, gaining a cult following.