Why is vodka filtered through charcoal?

Vodka is filtered over charcoal to remove flavour and aroma compounds from the distillate, leaving a drink that is as neutral as possible.

For most other spirits, the aim is the opposite. A whisky or a cognac must have character from the raw material and from the cask. Vodka is the category in which neutrality is the goal: Regulation (EU) 2019/787 prescribes that the alcohol is distilled or rectified in such a way that the organoleptic characteristics of the raw materials used and the by-products of fermentation are selectively reduced. Filtering over activated carbon is the final step in the same direction.

Nothing is added in that step. Something is only taken away, and that is precisely why the technique belongs with vodka and not with an aged whisky.

Activated carbon mainly binds higher alcohols, aldehydes and esters, the volatile by-products of fermentation that stand out as sharp or solvent-like in a neutral distillate.

Research into agricultural distillates shows how targeted this is. In a study in Food Additives and Contaminants (2017), one gram of activated charcoal per hundred millilitres of distillate at 50 percent by volume, with a contact time of one hour, gave the greatest reduction in the levels of aldehydes, alcohols and esters. Not everything binds equally well: acetaldehyde and methanol actually showed the lowest degree of adsorption.

The legislator works with the same substances. For agricultural ethyl alcohol, maxima apply of 0.5 gram of higher alcohols, 0.5 gram of acetaldehyde and 1.3 gram of ethyl acetate per hectolitre of alcohol of 100 percent by volume.

Activated carbon works by adsorption: molecules from the liquid stick to the internal surface of the carbon, which measures hundreds of square metres per gram.

Charcoal is activated with steam or chemically, which creates a fine network of pores. A technical report for the American National Organic Program gives food-grade activated carbon a surface area of 300 to 2,000 square metres per gram, with outliers up to 5,000. How much is bound depends on the type of carbon, on the substance itself, and on the concentration, the temperature and the contact time.

As a result, in practice it is not only how often filtering takes place that counts, but above all how slowly the liquid runs through the charcoal column.

Regulation (EU) 2019/787 stipulates that vodka contains at least 37.5 percent alcohol by volume and that treatment with activated carbon is permitted to give the drink special organoleptic characteristics.

The raw material is ethyl alcohol of agricultural origin from potatoes, from cereals, from both, or from other agricultural raw materials. That alcohol itself has a minimum alcoholic strength of 96.0 percent. For vodka, a stricter methanol limit also applies than for agricultural ethyl alcohol in general: a maximum of 10 grams per hectolitre of alcohol at 100 percent by volume, against 30 grams for the alcohol itself.

Flavourings may only be added as natural substances found in the distillate of the fermented raw materials, and without creating a dominant flavour. If the vodka does not come exclusively from potatoes or grains, the label must state “produced from …”, followed by the raw material used.

“Multiple filtered” is not a legally defined designation; European law sets no requirements for the number of filtration passes and attaches no quality judgement to it.

Technically the direction is predictable. The more often and the more slowly the spirit is filtered over activated carbon, the more volatile by-products are bound and the more neutral the result. The downside is that the last bit of character of the raw material disappears too. Anyone looking for a vodka in which the potato or the rye is still recognisable will therefore not automatically end up with the bottle with the highest number of filtrations on the label.

’t Bockje heeft 247 verschillende wodka’s op voorraad in de winkel aan de Brink in Bathmen, waarvan 71 ongearomatiseerd en 43 gearomatiseerd, uit twaalf landen, met Polen (66 flessen) als grootste herkomstland. Wij verkopen geen alcohol aan personen onder de 18 jaar. NIX18.