What is Chill Filtering?

2005-08-08

Chill filtering is getting more attention in the media and is increasingly
often a topic amongst whisky lovers. You have probably already noticed that
some bottles, for example the Ardbeg Ten year old, have ‘non chill-filtered’
written on the label. Even if it is not mentioned on the label, chances are
good that your whisky is non chill-filtered if it has an alcohol content of
more than 46 percent.

But what exactly is chill filtering and what happens during the process?
Chill filtering means that the whisky is cooled down to around 0 degrees
Celsius and is passed through a metal filter. The cooling and filtering
makes it possible to remove normally occurring fatty acids and some proteins
and esters. When the whisky is chilled, the unwanted substances clog
together and the increased particle size makes it possible to filter them
out. As a side effect, the cooling also makes it possible to remove bigger
particles such as coal fragments from the cask. The amount of discarded
particles depends on how fast the whisky is pumped through the filter; a
higher pressure and thus speed filters out fewer particles while a lower
pressure removes more particles. It is also possible to control the process
by varying the thickness of the filter or by using a series of
interconnecting filters. The temperature may vary between different
distillers and bottlers; blended whisky is often chilled to –4 degrees
Celsius because of the low natural concentration of fatty acids in the
grain.

The reason for chill filtering is mainly cosmetic; the producers want the
whisky to look good. They do not want the consumer to think s/he has bought
an inferior whisky when it clouds when mixed with water or when it is
chilled. Non chill-filtered whisky also has a tendency to develop sediment
if kept in a cool place.

There is an ongoing debate as to whether chill filtering affects the taste
or not. Most of the discussion only involves single malt whisky –virtually
all blended whiskies are chill filtered. In any event, advocates of
filtering argue that the taste is left completely intact and that the
filtering actually helps to maintain a good and consistent quality. Those
opposed are convinced that the elimination of fatty acids, which have been
shown to carry some of the flavor, is certain to alter the character of the
whisky.

Although the debate is sure to continue there is a definite trend towards
more Cask Strength and non chill-filtered bottlings. For example,
Bruichladdich Distillery actively advertises the fact that none of their
releases are chill filtered. To readers who wish to investigate the issue
further we can recommend the Gaelic whisky Té Bheag which may be bought both in a chill-filtered and non chill-filtered version.

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