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Telling when a bottle-conditioned cider is ready

How do I tell when a bottle-conditioned cider has finished conditioning?

In short

Conditioning is complete when the priming sugar has been fermented out, which at 15–20 °C usually takes two to four weeks, and after which the bottle needs further time cool for the yeast to settle and the carbonation to integrate.

The reliable indicators are a firm deposit at the base, a stable rather than rising pressure, and — most directly — opening a test bottle from the batch.

Time alone is not a sufficient indicator, because a cold store can suspend conditioning entirely and a warm one can complete it in days.

What is happening in the bottle

Bottle conditioning is a small, controlled secondary fermentation. A measured quantity of sugar and a viable population of yeast are sealed into a pressure-rated bottle; the yeast ferments the sugar; and because the bottle is sealed the carbon dioxide produced has nowhere to go but into solution and the headspace. The pressure produced is a function of how much sugar was added, not of how long the bottle sits.

That last point is the key one, and it disposes of a common worry. Once the priming sugar is gone, the pressure stops rising. A bottle left for a further year does not become more carbonated; it becomes a bottle whose yeast has settled and whose character has developed. Rising pressure after conditioning should have finished means there is more fermentable sugar in the bottle than there was supposed to be, which is a different and more serious situation.

Temperature governs the rate. Yeast works well between roughly 15 °C and 22 °C, slows markedly below about 12 °C, and is effectively dormant near freezing. A batch put straight into a cold store may not condition at all until it is warmed.

Once fermentation is complete, the yeast flocculates and settles, and the cider clears from the top down. The carbonation also changes character over the following weeks, moving from a coarse, aggressive fizz towards a finer and more integrated mousse.

A working sequence

Typical bottle-conditioning stages after bottling
StageTypical duration at 15–20 °CWhat to look for
Lag and start2–5 daysLittle visible change; yeast adapting
Active secondary fermentation1–3 weeksFine haze may develop; a test bottle shows rising carbonation
Fermentation completeFrom about 2–4 weeksTest bottle carbonation stops increasing between checks
Settling and clearing2–6 weeks, coolA firm deposit forms; cider clears from the top down
Integration1–3 months onwards, coolMousse becomes finer; the cider tastes less raw
Long-term developmentMonths to years, coolAutolysis character; phenolic softening in tannic ciders

Testing without wasting the batch

The standard method is a test bottle: fill one plastic bottle from the same batch at the same time as the glass ones, cap it, and store it alongside. A plastic bottle goes hard as pressure builds, and the difference between "gives under a squeeze" and "rigid" is easy to feel. When it stops getting harder between checks a few days apart, the fermentation has finished.

The direct method is to open one bottle from the batch and taste it. This costs a bottle and tells you everything: how carbonated it is, whether it still tastes of unfermented priming sugar, and whether the deposit has settled. Sampling one bottle at two weeks, one at four and one at eight builds a picture of the batch that no amount of external observation will.

Weighing is not practical at bottle scale, and pressure gauges fitted to a sacrificial cap exist but are seldom worth the complication. For a home batch the plastic-bottle test and one opened bottle answer the question.

Rising pressure after conditioning should have finished is a warningIf bottles keep getting harder weeks after the priming sugar should have been used up, something is fermenting that was not meant to — residual sugar the primary fermentation left behind, or a sugar-tolerant organism. That batch is heading towards over-carbonation. Move it somewhere cold immediately, keep it away from people, and open bottles with care and away from your face.

Common problems

Under-carbonation after a long wait usually means the yeast could not work: too cold, too little viable yeast at bottling, a cider too high in alcohol for the strain to restart, or a sulphite level that suppressed it. Warming the bottles to 18–20 °C for a fortnight resolves most cases where cold was the cause.

Wildly uneven carbonation across a batch means the priming sugar was not evenly distributed at bottling. Sugar added bottle by bottle, or syrup not properly mixed through the bulk, produces bottles that range from flat to dangerous within a single batch. Where this is suspected, every bottle in the batch should be treated as potentially over-carbonated.

A cider that never clears has a haze that is not yeast — pectin, protein or starch — and no amount of conditioning time will settle it. That is a fault carried in from earlier in the process, not a conditioning problem.

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