Ask Mr. Wizard

Keg-Conditioning Beer


Anthony Hoskins — Stavanger, Norway asks,

I was wondering how long I should be leaving my beer in the keg before I drink it. I know some people force carbonate and drink within 24 hours but surely, they must be drinking green beer. When bottling, I usually allow two weeks in the fermenter then at least two weeks in the bottle before tasting. Should the same rule apply to kegging and would the beer condition better if the keg was left at cellar temperature rather than being kept in the fridge?


Anthony, the short answer to your question is that it depends on when the beer was filled into your keg. In order to answer this question, a bit of background is required, so hang tight for a bit of review. There are many ways to go about managing the fermentation and aging process, but all methods share the same basic phases. Primary fermentation is generally quick, a bit raucous, especially when fermenting ales, and aromatic. This is when wort gravity falls from its original value at the onset of fermentation to a few ticks above the final gravity, yeast cells multiply and sometimes flow out of the fermenter along with carbon dioxide gas, hop and yeast aromatics, and bits of cold-break trub, and fermentation flavor compounds are synthesized. The young, sometimes rough, beer present in the fermenter at the end of primary is “green beer.”

Prior to the ubiquitous use of the uni-tank process, green beer was racked into some sort of vessel for aging. Lager brewers typically would rack beer from the primary into a lagering vessel for flavor maturation, clarification, and carbonation. One of the most reliable methods to accomplish these various goals was to blend green beer from primary with a bit of actively fermenting beer, so-called kräusen named after the high kräusen stage of fermentation, and allowing this mixture to age in a closed vessel for a period of weeks to months. Kräusening is still used today to produce traditionally brewed lagers by brewers small and large.

Traditional ale brewers did not kräusen their cask-conditioned ales, but the process is similar in many respects. Green ale, priming sugar, finings, and oftentimes hops, go into casks where the mixture rests and matures. During a 1–2 week rest, the cask comes into condition as the priming sugar is consumed by yeast, yeast and haze material settle to the bottom of the cask with the aid of finings, and hop aromas from the dry hop addition infuse into the maturing ale.

At the end of both of these aging periods, the result was beer in a ready-to-drink state. Although these traditional methods are still used, a substantial volume of beer these days is fermented and aged in a single vessel, and the processes used for ale and lager brewing are often indistinguishable aside from the yeast strains employed for fermentation and the times and temperatures used for the process. This means that beer can be fermented, carbonated, and aged in a single vessel, then transferred to a keg or bottle for easy storage and transport to the point of use. Not all brewers carbonate their beers in the fermenter, and a common variation on the uni-tank process is to move beer from the fermenter into a second vessel where the beer can quickly be carbonated before packing.

The point is that a quick carbonation process in a keg followed by immediate consumption is not necessarily synonymous with drinking green beer. If 3-day-old ale was racked into a keg before final gravity were achieved and before the beer had a proper diacetyl rest, immediately chilled, forced carbonated, and put on draft, then a pint of green beer would indeed be served; the missing portion of this abbreviated brewing process is beer maturation.

The old-school homebrewing norm is to ferment, age, and bottle with priming sugars for bottle conditioning. This method is greatly aided when flocculent yeast with good settling properties are used, and the maturation period can be conducted in the bottle provided sufficient aging times, healthy yeast, and moderate temperatures. Bottle conditioning is really just a variant of kräusening and cask conditioning. And of course, if your bottle is a bit larger in size, made of stainless steel, and referred to as a keg, this same process is named keg-conditioning.

If the keg in question, the one you just filled and are contemplating the merits of aging for a week or two versus tapping today, contains beer that was fermented to dryness, given a proper diacetyl rest, cooled to near 32 °F/0 °C and held for several days to improve beer clarity (or not if you are not after clear beer), and carbonated to the desired level, it can be consumed whenever. But if the keg in question was filled with green beer as soon as primary fermentation finished and is being held at moderate temperatures to allow for in-package maturation, then it should be treated like your bottle-conditioned beers.

Response by Ashton Lewis.