Arrested fermentation

What is actually happening

The yeast is removed or immobilised before it has consumed much sugar. It is the simplest route to a low-alcohol beer and needs no specialist equipment.

Its characteristic flaw is that most of the wort sugar is still there, so the beer tends to taste sweet and worty. Modern producers counter this with mash design that limits fermentable sugar, with souring, or by combining the technique with others.

What goes wrong here

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

• Unintended sweetness — Beer that finishes sweeter than intended, from under-attenuation, excess crystal malt, or a mash run too warm.
• Vegetal character — Cooked-vegetable notes that are not DMS — a residual category rather than a single compound.

Styles where this step is decisive

• Alcohol-free pale lager0–0.5% ABV

  A pale lager produced at or near zero alcohol, now the largest and most refined part of the no-alcohol category.

• Low-alcohol bitter0.5–2.8% ABV

  A genuinely fermented British ale brewed at very low strength, keeping cask character without dealcoholisation.

• Alcohol-free wheat beer0–0.5% ABV

  An alcohol-free wheat beer — often the most convincing of the category, because wheat body and yeast esters survive dealcoholisation well.

• Alcohol-free stout0–0.5% ABV

  An alcohol-free dark beer where roasted grain does most of the work — one of the more successful conversions in the category.

Related steps and concepts

• Vacuum distillation — The removal-based alternative.
• Maltose-negative fermentation — The yeast-selection alternative.