Peat sources and peat smoke character

What peat is

Peat is partly decayed plant material that builds up in waterlogged ground, where low oxygen and acidity slow rotting. It forms very slowly over thousands of years. Cut, dried and burnt, it gives a dense, aromatic smoke rich in phenolic compounds.

The plants that formed it matter. Peat from coastal bogs may be dominated by mosses and sedges. Inland and upland peat often contains more heather and woody material. Studies of peat smoke have found that peats from different places give different balances of smoke compounds. That is one reason whiskies at similar peating levels can taste quite different. Our guide to peat and smoke in whisky gives the drinker's view.

Smoke goes on in the kiln

Peat is burnt in the early stage of kilning, while the green malt is still damp. Damp grain picks up smoke much more readily than dry grain, so the timing sets the result. Peat is burnt at a low, smouldering temperature to make more smoke and less heat. Once the malt has dried, further peat smoke adds little.

Maltsters measure the result as phenols in the malt, in parts per million (ppm). Lightly peated malt might be under about 10 ppm. Heavily peated malt is commonly 40 to 50 ppm or more. Ask your maltster which method they use to measure, because different analyses give different numbers for the same malt.

The compounds behind the flavours

Peat smoke contains many phenolic compounds. A few do most of the work:

• Phenol and the cresols. Medicinal, antiseptic, sticking plaster.
• Guaiacol and related compounds. Smoky, bacon-like, campfire.
• Xylenols and others. Tarry, rubbery and earthy notes in combination.

The balance between these groups shapes whether a whisky reads as medicinal, sweetly smoky or ashy. Peat source, kiln conditions and later distillation all move that balance.

Much of the smoke is lost on the way

Malt phenols do not all reach the spirit. Some are lost in mashing and fermentation. Distillation changes the picture again, because the heavier phenols tend to come over later in the spirit run. The spirit cut is therefore a peat decision.

A distillery that cuts early keeps a cleaner, lighter new make with less smoke. A later cut into the feints picks up more of the heavier phenols and gives a smokier, oilier spirit. This is why two distilleries buying the same 50 ppm malt can produce new make with very different smoke levels. Still shape and copper contact play a part too. Our guides to lyne arm angle and copper contact explain how.

Smoke fades in the cask

Phenol levels in whisky fall during maturation as the spirit interacts with the cask and some compounds change or evaporate. A heavily peated new make can become noticeably gentler after years in wood. In hot Indian warehouses, where maturation moves faster, expect this softening to happen sooner than in a cool Scottish warehouse.

Plan for it. If you want a clearly smoky whisky at five years in Indian heat, you may need a smokier new make than a Scottish recipe for the same age would suggest. Track it by tasting retained samples against fresh new make.

Sourcing peated malt in India

India does not have a peat cutting tradition for malting, so peated malt is usually imported from maltsters who peat to order at stated ppm levels. That brings shipping time, cost and storage questions. Peated malt loses some of its phenols in storage, so buy close to use and store it cool and dry.

The floor detail we would insist on: keep peated and unpeated malt in separate, labelled storage and mill peated last before a clean. A mill that has just ground heavily peated malt will leave smoke in the next unpeated batch.

Decide the smoke you want before you buy

Start from the glass. Decide whether you want medicinal, sweet or ashy smoke and how strong at the age you plan to bottle. Then work back through cask, cut points and malt ppm. Buying 50 ppm malt and hoping is not a recipe. A distilling course that covers distillation cuts and maturation gives you the method to hit the target on purpose.

Your first step: ask your maltster for the phenol figure and measurement method on your current peated malt, then nose your new make at the start, middle and end of the heart cut.

Common questions

What is peat?

Peat is partly decayed plant material that builds up in waterlogged ground over thousands of years. Dried and burnt, it gives a smoke rich in phenolic compounds.

What does ppm mean for peated malt?

It is the level of phenols in the malt in parts per million. Lightly peated malt may be under about 10 ppm and heavily peated malt 40 to 50 ppm or more.

Why does peated whisky taste different from distillery to distillery?

Peat source, kilning, cut points, still shape and cask all change which smoke compounds reach the glass and in what balance.

Does peat smoke fade as whisky ages?

Yes. Phenol levels tend to fall during maturation. In hot climates this happens faster than in cool warehouses.