Freeze concentration

What is actually happening

Water freezes at a higher temperature than alcohol. Chill a beer below zero and part of the water crystallises out; remove the ice and everything left behind — alcohol, sugar, colour and flavour — is more concentrated than it was.

This is how eisbock is made, and the strength gain is real but bounded: the more ice removed, the harder the remaining liquid is to freeze further, so the practical ceiling is well short of a spirit.

It concentrates faults as faithfully as it concentrates virtues. A beer with a fusel edge or a trace of oxidation becomes a beer with a pronounced one, which is why the technique is only used on beer that was good to begin with.

It is legally distinct from distillation in most places because nothing is evaporated, but the line is a matter of local law rather than of chemistry, and BeerHQ does not state where it falls in any particular jurisdiction.

What goes wrong here

Risks rather than certainties. This step does not cause these faults; getting it wrong can.

• Fusel alcohol — Harsh, solvent-like alcohol heat from fermentation run too warm or under stress — distinct from the pleasant warmth of a strong beer.

Styles where this step is decisive

• Eisbock9–14% ABV

  A doppelbock concentrated by partially freezing it and removing the ice, intensifying malt, body and alcohol together.

• Doppelbock7–10% ABV

  Intensely malty strong lager, dense with bread crust, caramel and dark fruit, and remarkably clean for its strength.

Related steps and concepts

• Lagering — The cold conditioning it extends past freezing.
• Cold crashing — A related use of cold that stops short of ice.