Chill Filtering

Chill Filtering is a process used to filter out particulates that may cause a hazing effect in the liquid.

Chill Filtering is a process that occurs before bottling and consists of chilling a spirit down to a very low temperature (often around zero degrees), and once chilled, passing it through a filter to pick up tiny particles before it has the chance to warm up again.

It’s a practice that is very heavily associated (and debated) in Whisky production, but there are also some Rum and Gin producers who use the practice. The reason that some distilleries choose to Chill Filter their products is that at less than 46% ABV a cloudy haze, also known as louche, can form in the bottle at low temperatures.

The haze is caused by flocculation, of which there are two types - reversible and irreversible. When it occurs in Whisky it is almost always due to the ethyl esters of long-chain fatty acids, and larger alkyl esters which formed during the production (linked to factors like cut points during distillation). Some extracts from cask maturation can also contribute to reversible flocculation too, while for gin makers, the haze is caused by having an excess of essential oils derived from the botanicals used. If you warm up a bottle to a normal room temperature, these types of hazing will simply disappear.

Sometimes the haze is actually irreversible floc however, which takes the form of very small crystals of calcium oxalate. This tends to be derived from the water used to reduce the spirit prior to bottling which may have high levels of calcium or magnesium. This type of hazing will not disappear once the spirit returns to normal temperatures, and little white crystals will float about the bottom of the bottle.

The Chill Filtration process recreates the ‘haze’ moment where the flocculation is visible and strips it out, preventing it from re-forming once at normal temperatures.