Why does whisky turn cloudy when you add ice or water?

Chill haze occurs because long-chain fatty acid esters clump together into micelles as soon as their solubility drops. Those particles scatter light, which makes the whisky look milky or hazy.

It is mainly about esters with a long carbon chain, roughly C12 to C18. They come from fermentation and from the oak cask. Short-chain esters do stay in solution and carry aroma. Besides fatty acid esters, the specialist literature also names proteins and minerals such as calcium, magnesium, silicates and iron as a cause of haze.

Alcohol keeps the fatty acid esters in solution. Water lowers the alcohol percentage in the glass and ice also lowers the temperature, and then the esters precipitate together.

Around 46 percent alcohol by volume is the limit above which whisky stays clear at room temperature. If you add a splash of water to a whisky of 46 percent, the strength in the glass drops below that limit. A cube of ice does the same and also cools the glass, so both causes work at the same time.

Cold filtration cools the whisky to around freezing point and then presses it through filter plates. The precipitated esters stay behind in the filter, so the bottle stays clear even with ice.

In practice this happens at 0 to 4 degrees Celsius, in exceptional cases down to about 6 degrees below zero. A plate-and-frame filter with plates of diatomaceous earth, a powder of fossil diatoms, is used. Measurements in the specialist literature arrive after cold filtration at an average turbidity of 2.5 NTU.

Cloudiness caused by fatty acid esters is neither spoilage nor a production fault. It is a reversible physical phenomenon: once the whisky returns to room temperature, the haze usually dissolves.

Many bottlers therefore deliberately choose to bottle without chill filtration, usually at 46 percent or higher, and state that on the label. The European rules prescribe a minimum of 40 percent alcohol by volume for whisky and permit no other addition than caramel E150a for the colour. About filtration those rules say nothing.

In the shop on the Brink in Bathmen there are 3,897 different whiskies. Of these, 2,663 bottles are bottled at 46 percent alcohol or higher and 1,184 are between 40 and 45.9 percent.

Bottlings without chill filtration you find mainly in that first group, because bottlers usually combine that choice with 46 percent or higher. Whether a bottle is chill-filtered is not always stated on the label. If you ask in the shop, we will look it up for you.

First pour a sip neat and then add room-temperature water drop by drop. The strength in the glass then drops gradually and the temperature stays higher than with melting ice.

Raakt de whisky toch troebel, dan hoeft u niets te doen. Bij opwarmen tot kamertemperatuur trekt een sluier van vetzuuresters meestal weg. Leeftijd telt wel: NIX18, geen alcohol onder de 18 jaar.