Conditioning

What is Conditioning? Conditioning is the post-primary-fermentation stage of brewing where beer is matured, naturally carbonated, clarified, and stabilized before it reaches the glass. It happens in a secondary tank, in a cask, or directly in the bottle, and the beer is typically transferred off the spent yeast and debris so it is no longer exposed to compounds that can produce off-flavors such as acetaldehyde. Depending on the style and the brewer's intent, conditioning can last anywhere from two to four weeks to several months or even years. The result is a cleaner, rounder, and more expressive beer with the carbonation locked in.

How Conditioning Works

After primary fermentation, brewers move the young beer into a second container so it can mature away from the dead yeast and trub left behind. During this time, harsh flavour components developed during fermentation dissipate and the beer becomes smoother and more stable. A traditional technique called kräusening can be used to refresh CO2, in which actively fermenting wort is added to finished beer to restart fermentation and introduce fresh carbonation naturally.

Lagers take this idea the furthest. The word lager comes from the German for storage or storeroom, referring to the practice of holding beer in cool caves before drinking. Brewed with the bottom-fermenting yeast Saccharomyces pastorianus at cold temperatures, lagers are then lagered at cellar temperature or below for one to six months while still resting on the yeast, producing the clean profile the style is known for. Ale yeast, by contrast, works warmer, at roughly 18 to 24 C.

Bottle and Cask Conditioning

Bottle conditioning carbonates the beer inside the bottle itself. Brewers add a small dose of sugar or wort, a step called priming, so that a viable yeast population still in suspension produces CO2 that has nowhere to escape. The beer can be filled unfiltered straight from the fermentation tank, or filtered and then reseeded with fresh yeast. Warm fermentation typically runs around 15 to 20 C, while cool fermentation sits closer to 10 C.

Cask-conditioned ale, often called real ale, takes a different route. Unfiltered, unpasteurized beer goes into metal, plastic, or wooden casks where secondary fermentation continues right up to the moment it is served, with live yeast still slowly at work. To keep the beer fresh once a cask is tapped, a cask breather can introduce low-pressure CO2 to replace what has been drawn off and block ambient air; CAMRA updated its policy to accept this practice in 2018. The style remains a meaningful part of the British market, with cask-conditioned ale selling 420 million pints in the UK in 2019, equal to 13.5% of total pint sales.