What is chill haze in whisky?

Pour a whisky, add a splash of water, and every so often the glass turns cloudy. Chill the bottle and the same thing happens. It looks like a fault, and people do send bottles back over it.

Nothing has gone wrong. The cloudiness comes from compounds the spirit has been carrying since fermentation, held in solution while the strength and the temperature stay up and coming out of it when either falls. Leave the glass in a warm room and it usually clears again.

Jim Swan traced those compounds at Inveresk, from 1968, in a laboratory that was not a whisky laboratory at all. The answer was the fermentation rather than the cask, though it is still filed in most places under filtration.

It is a malt whisky difficulty rather than a grain one, and the reason lies in the difference between a pot still and a continuous column. Bottlers had already found their own answer long before anyone explained the cause, which was to chill the whisky and filter out whatever came out of solution before it reached a bottle. That is what non chill filtered means on a label: the step was left out, and the bottle may cloud.

Where the whisky was going mattered here. The export trade was led at the time by the lighter blends, J and B and Cutty Sark among them, and a bottle that clouds on the far side of an ocean is a problem the shipper cannot see coming. Answering it showed the industry what research of that sort was worth. Eight of them broke away in 1970 to work on whisky alone, and by 1974 twelve competing firms were funding them together as Pentlands Scotch Whisky Research.