Tannin and colour from the cask

New make is colourless

Spirit leaving a pot still or column still is clear. Distillation leaves colour behind in the wash. So every shade of gold, amber or mahogany in a bottle comes from one of two places: the oak cask during maturation or caramel colouring added before bottling. Our guide to maturation and casks covers the cask side.

Where the colour comes from

Toasting and charring a cask breaks down wood compounds in the inner layers. Hemicellulose turns into caramelised sugars. Lignin and tannins break into other coloured compounds. Spirit dissolves them gradually. The more active the wood, the faster colour builds.

A first-fill cask, used for whisky for the first time after its previous contents, gives the most colour. A refill cask on its second or third use gives much less. Previous contents matter too: a cask that held dark sherry passes on some of that wine's colour along with the wood's own.

Tannin is the grip

Tannins are a group of compounds in oak. In whisky they give a drying, slightly puckering feel on the gums and tongue, like strong black tea. European oak, the usual wood for sherry casks, is far richer in tannin than American white oak. That is why sherry cask whiskies often feel firmer and drier, while ex-bourbon whiskies feel softer.

Tannin also takes part in slow oxidation reactions during maturation. A little gives structure. Too much makes a whisky bitter and woody. Blenders watch for that edge.

Why colour is a poor guide to age

• Cask activity varies. A whisky from a lively first-fill cask can be darker at five years than a refill cask whisky at fifteen.
• Climate changes speed. Hot warehouses, like many in India, extract colour much faster than cool Scottish ones.
• Cask size matters. Small casks have more wood per litre and colour faster.
• Caramel can be added. In Scotch, plain caramel colouring (E150a) is permitted to keep colour consistent from batch to batch.

Our guide to whisky label terms explains how to read age statements, which tell you far more than colour.

Caramel colouring, briefly

Blenders use small amounts of caramel to keep a brand's colour the same across batches, since natural cask colour varies. Its effect on flavour at those levels is a debate among enthusiasts. Some bottlers label their whisky as natural colour to signal none was added. Labelling rules differ by country (and in India by state), so a bottle that says nothing may or may not contain caramel. See chill filtration and caramel colouring for more.

How to read colour and tannin in a tasting

Hold the glass against a white sheet of paper in daylight. Note the shade: pale straw, gold, amber, copper or deep mahogany. Pale often suggests refill or ex-bourbon casks. Deep red-brown often suggests sherry or wine casks, or added caramel.

Then sip a small amount and hold it for a few seconds. Notice whether your gums feel dry afterwards. That dryness is tannin. Compare an ex-bourbon whisky with a sherry cask whisky and the difference is usually clear. Keep water on the table, pace yourself and never drink and drive.

Colour in the cask as a working signal

Distillers do use colour, just not as a measure of age. In a warehouse, a quick look at a sample in a glass tells a blender how active a cask has been. A refill cask that has barely coloured its spirit after several years may need moving to a fresher cask. A small first-fill cask darkening quickly in a hot store may need tasting more often, because tannin climbs with colour.

Some distilleries measure colour with a simple colour meter so that samples can be compared across years. For a drinker, the takeaway is the same: colour tells you something about the wood, a little about the climate and nothing certain about the calendar.

One more caution. Light can affect colour over long periods, so a whisky kept on a sunny shelf may fade a little. That is another reason to store bottles away from windows.

Line up three glasses by colour

Next time you have a few whiskies to hand, pour small measures and line them up from palest to darkest before tasting. Guess which will taste oldest and woodiest. Then taste and check the labels for age and cask type. Most people find their colour ranking and their taste ranking disagree at least once, which is exactly the lesson.

Common questions

Where does whisky get its colour?

From the oak cask, as spirit dissolves compounds from the toasted and charred wood, or from caramel colouring added before bottling.

Does darker whisky mean older whisky?

Not reliably. Cask activity, climate, cask size and added caramel all change colour, so the age statement is a much better guide.

Why do sherry cask whiskies feel drier?

European oak, used for many sherry casks, contains more tannin than American oak, which gives a firmer, drying feel.