Carbonation
Natural carbonation
Bottling before the primary fermentation has finished, so the sugar still in the cider produces the carbonation with nothing added and nothing restarted.
Known as Méthode ancestrale where it originates. Also called Méthode ancestrale, Pétillant naturel, Pét-nat, Bottling on residual sugar.
- Stage
- Carbonation
- Traditional in
- Normandy, Pays d’Auge, Asturias, Basque Country and 1 more
- What it most changes
- Sweetness up, carbonation up
- Safety
- Carries a safety consideration — see below
This is the highest over-pressure risk of any carbonation route, because the maker is judging how much fermentable sugar remains rather than adding a known amount, and an underestimate keeps fermenting until the bottle fails. Use only bottles rated for sparkling products and closures — crown caps or wired stoppers — that will hold the pressure or vent before the glass does; never use still-wine bottles or screw-capped bottles. Store the bottled cider cold to slow the fermentation, monitor sample bottles regularly rather than assuming the ferment has stopped, wear eye protection and gloves when handling and opening, keep bottles out of warm spaces and away from where people work or sit, and open only when thoroughly chilled. A bursting bottle throws glass at speed and has caused serious injury.
What it is
Natural carbonation puts the cider into its final bottle while the primary fermentation is still running, so the sugar remaining in the liquid ferments in the sealed container and the gas it produces dissolves there. Nothing is added — no priming sugar, no cultured yeast, no dosage. The distinction from bottle conditioning is that no second fermentation is started: the original one is simply interrupted by the act of bottling and allowed to finish under pressure. It is the méthode ancestrale of French practice, the logic behind Norman bottled cidre, and the basis of modern pétillant naturel.
Why it is used
- It produces a naturally sweet, lightly sparkling cider without back-sweetening, because the sugar that would have fermented out is instead retained under the pressure that builds in the bottle.
- It requires no additive, no injected gas and no second yeast, which is why it remained the normal route in traditional cider regions long before pressure equipment existed.
- The gas and the sweetness are produced by the same fermentation, so the balance between them belongs to that particular batch rather than being assembled from separate decisions.
- It carries the fruit character of the primary ferment directly into the bottle, without the intervening racking, filtration and gas handling that other routes involve.
How it works
- A fermentation slowed by cold, by low nutrient availability or by successive rackings is bottled while unfermented sugar remains. The yeast continues to work in the bottle, and the carbon dioxide it produces cannot escape, so it dissolves and the bottle comes under pressure.
- Pressure and dissolved carbon dioxide themselves inhibit the yeast to a degree, and cold storage inhibits it further, so a fermentation bottled at the right point can stall short of dryness and leave residual sweetness under gas.
- The maker is estimating how much fermentable sugar remains rather than adding a known quantity. Gravity measurement gives a figure, but it cannot distinguish fermentable sugar from unfermentable sorbitol and other dissolved solids, and it cannot say whether the yeast will keep going.
- The yeast that made the cider stays in the bottle and settles as a deposit, so the finished drink is cloudy or throws sediment unless it is decanted, and the bottle is normally stored and sold cold to hold the fermentation where it stopped.
- In the Norman version, keeving has already stripped the must of the nitrogen the yeast needs, so the fermentation is naturally slow and weak and can be bottled with substantial sugar still present without running away.
What it changes
The direction this step pushes the finished drink in, dimension by dimension. A direction, not a measurement: how far it moves depends on the juice, the temperature and how the step is carried out.
| Dimension | Direction | Why |
|---|---|---|
| Sweetness | Raises | Bottling before the sugar is exhausted, and holding the cider cold and under pressure, leaves fermentable sugar in the drink that would otherwise have been consumed. |
| Carbonation | Raises | The tail of the primary fermentation continues in a sealed container, so the gas it generates has nowhere to go but into solution. |
| Fruit character | Preserves | The cider goes into the bottle straight from an active ferment without the transfers and treatments that strip volatile fruit aroma along the way. |
The chemistry and the organisms
What is actually being changed, and by what. Each entry says what that compound or organism does in cider generally; this page is one place it does it.
Compounds involved
Carbon dioxide
The other product of fermentation, which protects a cider from air while it is being made and, dissolved in the finished drink, changes both its texture and its perceived acidity.
Glucose
The sugar yeast takes first and the smallest of the three in apple juice, which is why the last sugar left in a slow ferment is almost never glucose.
Fructose
The dominant sugar of apple juice and the sweetest of the common sugars, which is why apple juice tastes sweeter than its total sugar figure implies and why a stuck ferment leaves sweetness behind.
Ethanol
The alcohol yeast makes from fruit sugar, which converts a perishable juice into a keepable drink and carries most of its aroma to the nose.
Pectin
The structural polysaccharide of fruit cell walls, which decides how much juice a press releases, whether a cider ever clears, and whether keeving is possible at all.
Organisms involved
Saccharomyces cerevisiae
The yeast that finishes essentially every cider, whether it arrives in a sachet or from the fruit, the press and the vessel.
Saccharomyces uvarum
A cold-tolerant relative of S. cerevisiae recovered from spontaneous cider and wine ferments, associated with low-temperature fermentation and higher glycerol.
Hanseniaspora valbyensis
The apiculate yeast most consistently reported as dominating the first days of a spontaneous cider fermentation, and a major contributor to its aroma.
Where it is traditional
The places this step belongs to as a matter of practice. It is not a claim of exclusivity — a method can be traditional in one region and perfectly ordinary in another.
What it is done with
Bottles and pressure: what glass will and will not hold
Sparkling-wine bottles are engineered and tested to hold several atmospheres; still-wine bottles are not engineered to hold any, and filling one with a carbonating cider is the most dangerous ordinary mistake in home cider making.
Airlocks, bungs and headspace management
An airlock is a one-way water trap that lets carbon dioxide out of a vessel while keeping air, insects and dust from coming in — a small component that solves the largest single problem in small-scale cider making.
What can go wrong
Faults that begin at this step, or that this step makes more likely. Each one is set out with its causes and whether it can be put right.
Bottle over-carbonation
More dissolved carbon dioxide in the bottle than intended or than the glass is rated for — a presentation problem at the mild end and a physical hazard at the severe one.
Gushing
Cider that erupts from the bottle on opening, either because it is over-pressurised or because something in it is nucleating the dissolved gas violently.
Excessive sediment
More deposit in the bottle or vessel than the presentation intends, ranging from a normal conditioning yeast layer to a loose sludge that clouds every pour.
Unwanted refermentation
Fermentation restarting in a sealed container, generating carbon dioxide that was not planned for and pressure that a bottle may not withstand.
Yeast haze
Cloudiness from yeast cells that have not settled out, usually because the strain flocculates poorly or the cider has not been left alone long enough.
Styles it produces
Categories in which this step is characteristic or required. Some name it in their definition; for others it is simply how they have always been made.
Pétillant cider
Lightly carbonated cider in which the gas is felt as a prickle rather than a stream of bubbles, the level most traditional bottle fermentation reaches on its own.
Cidre doux
The sweet tier of the French cider scale, defined since 2025 by a density at or above 1.024 together with an acquired strength no greater than 3% vol, so that the sweetness is demonstrably unfermented juice sugar.
Cidre de Normandie
Protected Normandy cider made from the region’s bitter and bittersweet fruit, characteristically low in alcohol, sweet-edged and lightly sparkling.
Cidre Pays d’Auge
The controlled appellation cider of the Pays d’Auge in Calvados, made by keeving from bitter Norman fruit and bottle-conditioned to a low alcohol and a high residual sugar.
Sidra espumosa
Sparkling Asturian cider made by a second fermentation under pressure or in bottle, presented as a fine sparkling drink rather than in the still poured tradition.
Keeved cider
Cider clarified before fermentation by a pectin gel that strips nutrients from the juice, producing a slow ferment that stops naturally with sugar still in solution.
More on natural carbonation
The whole method rests on one judgement: when to bottle. Bottle too early and the yeast has a large sugar reserve still to work through, and the pressure keeps rising until either the closure vents or the glass fails. Bottle too late and the ferment finishes in the bottle before it has generated enough gas, leaving a flat, dry cider. Between those lies a window that depends on how much fermentable sugar is left, how vigorous the yeast still is, how cold the store will be, and how much of the sugar is actually fermentable at all. Gravity gives a reading but not an answer, because unfermentable sorbitol — abundant in perry pears and present in apples — sits in the same measurement as the sugar that will ferment.
The traditions that rely on it have each found a way of making the yeast weak before the bottle rather than trusting the timing alone. In Normandy and the Pays d’Auge keeving is the mechanism: the chapeau brun takes nitrogen and much of the suspended matter out of the must, so the fermentation is slow and undernourished from the start and will stall of its own accord well short of dryness. That is why a cidre doux can be bottled with real sweetness and only reach a modest pressure. In Asturias and the Basque Country the bottled sparkling styles work from a different base — the same fruit and cellar as sidra natural, bottled to retain gas — and the modern pétillant naturel movement in cider has adopted the approach as a stylistic position: nothing added, sediment left in, the bottle presented as it comes.
What goes wrong falls into two categories, and only one of them is a quality problem. The quality failures are variability — bottles from the same batch finishing at different pressures and different sweetness because the yeast in each is a slightly different population — cloudiness, and a deposit that is disturbed by handling. The safety failure is bottle rupture, and it is not rare in careless hands. Because the pressure is generated by an ongoing fermentation whose end point was estimated rather than set, an underestimate has no natural limit: the yeast keeps working and the pressure keeps climbing. Cold storage, pressure-rated glass, secure closures and periodic opening of sample bottles are not refinements of the method. They are what makes it safe to practise at all.
Related processes
Steps that sit alongside this one, replace it, or depend on it having been done.
Fermentation
Keeving
Forming a floating pectin gel that lifts nutrients and solids out of the juice, so that the ferment starves before it finishes and leaves natural sweetness behind.
Carbonation
Bottle conditioning
Carbonating cider by letting a second fermentation finish inside the sealed bottle, so the gas is generated where it is going to stay.
Carbonation
Priming
Adding a measured, calculable quantity of fermentable sugar at bottling so that the fermentation which follows generates a predictable volume of carbon dioxide.
Fermentation
Arrested fermentation
Deliberately halting a ferment while sugar remains, to obtain natural sweetness from the fruit rather than from an addition — and accepting the instability that follows.
Fermentation
Gravity measurement
Measuring the density of juice or fermenting cider to follow sugar depletion and estimate alcohol, with the instrument limits and the perry complication that make the number less simple than it looks.
Packaging
Bottle pressure management
Matching the pressure a carbonated cider will actually generate to glass that can contain it, taking account of temperature and of any fermentable sugar left in the bottle.
What people ask next
Questions readers ask about the things this page mentions. Each one goes to the section that answers it rather than to a page written to receive the question.
- How do i know when my cider has finished fermenting — Take two hydrometer readings several days apart: if the gravity has not moved, the ferment is over. Airlock activity is not a reliable test, because a slow ferment can produce gas too slowly to see.
- How do you stop cider from fermenting — By removing the yeast, by chilling, by filtering it out, by pasteurising, or by a combination — and in practice a home maker cannot reliably stop a ferment mid-way with chemicals alone. Sorbate prevents yeast multiplying but will not stop an active ferment.
- How is sparkling cider made
- How much pressure builds up in a bottle of cider — Enough to matter. Every gram of sugar fermented in a sealed bottle produces gas, and a bottle not rated for it can fail. The French cider appellations require a minimum of 1.0 to 1.5 bar at 20 °C, and a bottle-conditioned cider can go well beyond that if it was filled with more sugar than intended.
- What is keeving — Keeving is a technique for starving a ferment of nitrogen so that it stops before all the sugar is gone, leaving a naturally sweet cider. Pectin is made to gel and float as a brown cap, carrying nutrients and yeast out of the juice with it.
- What is priming sugar — Priming sugar is a measured dose of sugar added at bottling so that the remaining yeast produces carbon dioxide inside the sealed bottle. Too much of it is the usual cause of burst bottles.
Where to go next
- How cider is made — The whole sequence, stage by stage, with the choices open at each one.
- Cider science — The chemistry and microbiology the methods on this page rest on.
- Troubleshooting — What goes wrong, how to recognise it, and whether it can be reversed.
Sources
What this page rests on. Where a source is marked as registered rather than read, CiderHQ is recording that the body is authoritative on the subject without claiming to have worked through the document itself. See our evidence policy for what each state means.
The New Cider Maker’s Handbook: A Comprehensive Guide for Craft Producers
Claude Jolicoeur, Chelsea Green Publishing, 2013. ISBN 9781603584739 · reference work · bibliographic record verified, not opened 2026-08-25
Bibliographic record verified on 2026-08-25 against the Open Library union catalogue: Chelsea Green Publishing, 2013, ISBN 9781603584739, one edition recorded. That establishes the citation points at a real book in a stated edition, which is what a citation needs and is all it establishes. No copy was opened and nothing is quoted from it. The book itself is in print and not digitised in any open collection; where CiderHQ needs a figure from this territory it uses an accessible research source instead and says so.
Institut Français des Productions Cidricoles (IFPC)
IFPC · research institute · retrieved 2026-08-24
The French technical institute for cider production. The authority for the French cultivar classification families, for keeving as an industrial process, and for the pectin and nitrogen chemistry that keeving depends on.
Servicio Regional de Investigación y Desarrollo Agroalimentario (SERIDA)
Principado de Asturias · research institute · retrieved 2026-08-24
The Asturian regional agri-food research service, and the technical authority behind the Asturian cultivar classification and the analysis of sidra natural. SERIDA’s own site has not been opened; what CiderHQ has read is SERIDA’s varietal characterisation as republished by the Consejo Regulador of DOP Sidra de Asturias, which credits it explicitly. The Asturian measurements therefore cite the Consejo rather than SERIDA — citing the body that did the work, at a document CiderHQ has not seen, would be exactly the kind of borrowed authority this register exists to prevent.