Islay whisky making

Distilling on Islay Peat

Peat is an organic material formed when plant matter partially decays in an environment without oxygen. In Scotland it is primarily composed of wetland vegetation including Sphagnum moss, heather and sedges. Peat itself can hold water, which in turn leads to expansion as further plant matter continues to decay. Under the correct conditions, peat is the first step in coalification – the conversion of plant matter into coal. The full process takes hundreds of millions of years, with peat appearing after thousands.

The plants and conditions that have come together to create a peat bog have a large impact on its character when burned. In the case of whisky making, the flavour that its smoke will impart to malting barley is key, and peats from different parts of the world will create different flavours. The island of Islay is largely composed of peat, and peat from the island gives a famously medicinal character to barley. The phenol-heavy character is usually attributed to the large amount of Sphagnum in Islay’s peat. Peat cut in other areas of Scotland give very different flavours, with Highland peat giving earthier notes thanks to the presence of more woody plants, and heather-rich Orcadian peat famously having a more floral character.

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Manually extracting peat is a traditional job across Scotland, and cutting by hand still practised despite the development of harvesting machines. To cut peat, the top layer of soil is peeled away, revealing the damp peat underneath. Traditionally, rectangular blocks are then cut using tools consisting of a handle and an angled blade – these vary in size and shape from short spades to more complicated long-handled tools – and then left to dry for up to weeks, depending on the weather. Once dried to the desired level, the peat bricks are stacked to dry further, which can take several months. Once fully dried, the peat is ready to use as fuel.

In the early days of malt production in Scotland, peat was a primary fuel source. Along with heat, peat produces pungent smoke which the barley absorbs, creating the famously smoky flavour for which many Scotch whiskies are well known. However, as transport routes opened up and alternative fuels, such as anthracite and coke, became more readily available, the use of peat as a primary heat source decreased. As the smoky flavour is a key component of many whiskies, these days peat is used simply as a flavouring agent, with controlled burning during the early stages of kilning introducing smoky flavours into the barley.

The smoke is rich with flavour compounds, including phenols such as cresol, guaiacol and eugenol, which are absorbed by the barley and also adhere to the husk. Some of these compounds will survive the production process, bringing with them the traditionally smoky flavour.

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