Chill filtering is a method in whisky making for removing residue. In chill filtering, whisky is cooled to between -10° and 4° Celsius (often roughly 0°) and passed through a fine adsorption filter. This is done mostly for cosmetic reasons – to remove cloudiness, rather than to improve taste or consistency.
Chill filtering prevents the whisky from becoming hazy when in the bottle, when served, when chilled, or when water or ice is added, as well as precluding sedimentation from occurring in the bottles. Such clouding only happens at an alcohol by volume of 46% or less, thus stronger bottled whisky is non-chill filtered or un-chillfiltered.
Chill filtering works by reducing the temperature sufficiently that some fatty acids, proteins and esters (created during the distillation process) precipitate out so that they are caught on the filter. Single malt whiskeys are usually chilled down to 0°C, while the temperature for blended whiskey tends to be lower since they have lower levels of fatty acid.
Factors affecting the chill filtering process include the temperature, number of filters used, and speed at which the whiskey is passed through the filters. The slower the process and the more filters used, the more impurities will be collected, but at increasing cost.
Since this process is believed to sometimes affect the taste of the whisky, for example by removing peat particles that contribute to the 'smokiness' of the flavour, some distilleries pride themselves on not using this process. For example, the Aberlour Distillery's distinctively flavoured A'bunadh whisky and Laphroaig's Quarter Cask bottles are not chill-filtered. Skipping the chill filtering step also reduces production costs. Springbank Distillery in Campbeltown pride themselves on having never chill-filtered their whisky throughout their entire history.