Maturation
Topping up
Refilling a maturing vessel as evaporation and racking losses lower the level, so that no significant surface of cider is ever left in contact with air.
Known as ouillage where it originates. Also called Ouillage, Keeping the cask full.
- Stage
- Maturation
- Traditional in
- Normandy, Pays d’Auge, Somerset, Herefordshire and 1 more
- What it most changes
- Oxidative character down
- Safety
- None recorded
What it is
Topping up is the routine of adding cider to a vessel that has lost volume, keeping it filled to the bung or to the top of the tank. Losses come from evaporation through the wood, from the small quantity left behind at every racking, and from sampling. The cider added is normally the same batch or a compatible one held for the purpose. It is unglamorous, it costs a keeping stock that could otherwise be sold, and in a wooden cellar it is close to non-negotiable, because an air space above cider in a cask is a habitat rather than an inconvenience.
Why it is used
- Acetic acid bacteria need oxygen at the liquid surface to oxidise ethanol to acetic acid, and denying them a surface in contact with air is the most effective control there is.
- Film-forming yeasts colonise a still, exposed cider surface as a visible skin, metabolising ethanol and leaving the drink thin and flat well before any vinegar character appears.
- Wood loses liquid continuously to evaporation, so a cask that was full when it was closed will not be full six months later unless somebody attends to it.
- A full vessel has almost no headspace for volatile aromatics to partition into, which limits aroma loss over long maturation.
How it works
- Oxygen enters a headspace far faster than it can diffuse into a static liquid, so the reaction zone for both acetic acid bacteria and film yeasts is the thin surface layer — eliminating the surface eliminates the zone.
- Acetobacter and Gluconobacter species oxidise ethanol first to acetaldehyde and then to acetic acid, and the acetic acid then esterifies slowly with ethanol to give ethyl acetate, which is the solvent note that usually announces the problem before the vinegar does.
- Film yeasts such as Pichia membranifaciens and Candida species form a hydrophobic pellicle at the interface and respire ethanol and organic acids, so their damage is depletion rather than off-flavour production.
- Where topping up is impractical, displacing the headspace with carbon dioxide, nitrogen or argon achieves the same end by removing the oxygen instead of removing the space.
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 |
|---|---|---|
| Oxidative character | Lowers | Removing the air space removes the interface at which dissolved oxygen is continuously replenished, so oxidative reactions run only on what is already in solution. |
| Freshness | Preserves | A vessel with negligible headspace loses very little volatile aroma to partitioning, and the cider that comes out resembles the cider that went in. |
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
Acetic acid
The vinegar acid, made by bacteria oxidising ethanol whenever air reaches a cider, and the one fault in cider that no later processing can undo.
Ethyl acetate
The most abundant ester in cider, giving lift and pear-drop at low concentration and nail varnish at high, and the earliest audible warning that acetic bacteria are at work.
Dissolved oxygen
Essential to a healthy yeast population at the start of fermentation and the principal enemy of a cider from the moment fermentation ends.
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.
Acetaldehyde
The compound sitting one step short of ethanol, which smells of bruised apple and sherry, binds most of the sulphite added to a cider, and is the chemical signature of oxidation.
Organisms involved
Acetobacter aceti
An acetic acid bacterium that oxidises ethanol to acetic acid wherever cider meets air, and the organism behind most volatile acidity in cider.
Acetobacter pasteurianus
The film-forming acetic acid bacterium of traditional vinegar production, and a common cause of surface growth and volatile acidity in cider.
Gluconobacter oxydans
A sugar-preferring acetic acid bacterium abundant on damaged fruit and in fresh juice, which oxidises glucose to gluconic acid before fermentation begins.
Film yeasts
A functional grouping rather than a taxon: the oxidative yeasts that form a skin on cider exposed to air and consume its alcohol and acid.
Pichia membranifaciens
A film-forming yeast that grows as a skin on the surface of cider left in contact with air, consuming ethanol and acid and leaving the cider thin.
Candida species
A large, historically artificial grouping of yeasts that appears throughout cider microbiology, containing organisms with little in common beyond the absence of a sexual stage.
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
The floating lid and the variable-capacity tank
A floating lid is a disc that rests on the surface of the cider and seals against the tank wall with an inflatable gasket or a liquid-filled channel, so a part-full vessel carries no headspace at all — which is the only problem the design exists to solve, and a large one.
Inert gas: carbon dioxide, nitrogen and argon
Gas is used to push air out of tanks, bottles, kegs and lines, and the three common gases are not interchangeable: carbon dioxide dissolves readily and will carbonate a cider, nitrogen barely dissolves at all, and argon is heavy enough to lie on a surface.
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.
Acetification
The active conversion of a cider’s ethanol into acetic acid by acetic acid bacteria at an air interface — the process, running in the vessel, that produces volatile acidity.
Volatile acidity
The measurable fraction of acidity that can be steam-distilled off, dominated by acetic acid and read as vinegar sharpness in the nose and a hard, hot finish.
Film yeast growth
A pale, powdery or wrinkled film of aerobic yeast growing on the surface of a standing cider, consuming alcohol and acid and producing acetaldehyde.
Oxidation
The cumulative effect of oxygen on finished cider: fruit aroma flattens, colour deepens towards amber, and a bruised-apple or sherry-like character replaces the fresh one.
Flat and lifeless
A cider with nothing obviously wrong and nothing to say: aroma faded, acidity dulled, finish short — usually the cumulative result of over-processing or slow oxidation.
Acetaldehyde excess
A bruised-apple, green-nut or sherry aroma from acetaldehyde, produced by oxidation, by film yeast, or left behind by a ferment that was interrupted.
Ethyl acetate taint
A solvent, nail-varnish or pear-drop aroma from ethyl acetate, the most abundant ester in cider and the one that turns from lift to fault over a narrow range.
Vinegar fly contamination
Small flies carrying acetic acid bacteria and spoilage yeasts directly into juice and cider, and depositing them wherever they land.
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.
West Country farmhouse cider
Cider made on the farm from tannic bittersweet fruit, wild-fermented in wood and sold still and unfiltered, in a tradition whose variability is one of its defining features.
Cidre fermier
Farm-made French cider, pressed and fermented on the holding that grew the fruit, sold as an agricultural product of that farm rather than as a regional or industrial one.
Sidra natural
The still, dry, unfiltered cider of Asturias and the Basque Country, wild-fermented from local high-acid fruit and poured from a height to raise a momentary sparkle.
Barrel-aged cider
Cider matured in wood, where slow oxygen ingress, extraction from the staves and the barrel’s resident microflora all change the finished drink.
More on topping up
The reason a partly empty wooden vessel is dangerous and a partly empty steel one is merely careless comes down to what lives in the wood. Acetic acid bacteria are present in almost any cider cellar and are established in the staves of any cask that has held cider before. They are strict aerobes and they work at the interface, so a full cask keeps them effectively dormant and a three-quarters-full cask hands them a working surface, a food supply and a continuously replenished oxygen supply through the bung and the wood. The progression is predictable: a lift of ethyl acetate first, then rising volatile acidity, then a cider that is plainly on its way to vinegar. Nothing recovers it. This is why the French cellar vocabulary has a specific word for the operation, ouillage, and why it is treated as a scheduled task rather than an occasional tidying.
The practical difficulty is that topping up requires keeping stock of the same or a compatible cider, held sound, for exactly this purpose. A small maker who has bottled everything has nothing to top up with, and the usual improvisations — topping with a different batch, or with juice, or with water — each carry a cost, whether to the identity of the cider, to its microbial stability, or to its strength. The alternative is to consolidate: as levels fall, combine vessels so that fewer of them are full rather than several being part-full. Where neither is possible, inert gas is the modern answer, and it works, but it needs a vessel that will actually hold a blanket. A traditional cask will not hold gas for long, so in wood the volume, not the atmosphere, is what must be managed.
A wrinkle worth knowing is that in some traditions the exposure is deliberate. Certain oxidative styles are made in vessels held intentionally short, and the character sought is precisely the one that topping up prevents. That is a different process, undertaken with a cider chosen for it, and it is not what happens when an ordinary cask is neglected. The distinction is between a controlled oxygen exposure to a robust, tannic, alcoholic cider and an uncontrolled one to whatever happens to be in the cellar. Ordinary maturation, in every tradition surveyed here, assumes a full vessel.
Related processes
Steps that sit alongside this one, replace it, or depend on it having been done.
Maturation
Barrel ageing
Holding cider in wood — which may mean an old neutral vat used simply as a vessel, or fresh or spirit-seasoned oak used as a source of flavour, and the two are not the same operation.
Maturation
Racking
Moving cider off the sediment it has thrown, which both cleans the liquid and — by taking yeast and nitrogen away with the deposit — slows what is left of the ferment.
Maturation
Tank maturation
Resting cider in stainless steel or a lined vessel, where the point of the container is that it contributes nothing and admits almost no oxygen.
Storage
Cellar storage
Holding packaged cider in conditions that let it change slowly and predictably, where stability of temperature matters more than the temperature itself.
Juice treatment
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
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 sterilise cider bottles — Wash them clean first, then sanitise with a no-rinse sanitiser or a sulphite solution, and fill while still wet with it. Bottles that look clean but have dried deposits inside are the usual source of bottle spoilage.
- How should i store cider — Cool, dark and at a steady temperature. Light causes light-strike in clear glass, warmth accelerates oxidation, and temperature swings push cider past the closure of a bottle that is not tightly sealed.
- What is racking in cider making — Racking is siphoning cider off the sediment it has thrown into a clean vessel, leaving the lees behind. It clarifies the cider and, in traditional practice, is also used to slow a ferment by removing yeast with the lees.
- Why does my cider taste like vinegar — Acetic acid bacteria have reached the cider and, given air, are converting its alcohol into acetic acid. The cause is almost always oxygen — an unfilled vessel, a leaking bung, or a slow transfer.
- What are carbon dioxide, nitrogen and argon used for in cider making, and how dangerous are they — Air is what damages finished cider, and the cheapest way to remove air is to displace it with a gas that will not react with the cider. That is the whole purpose of inert gas in a cider house.
- Can you fix a cider that has gone vinegary — Not really. Volatile acidity cannot be removed at small scale, and blending it away only dilutes it. The realistic options are to accept it, to blend a lightly affected batch into a much larger sound one, or to let it finish becoming vinegar.
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.
Cider and perry production technical training material
Peter Mitchell / Cider and Perry Academy · reference work · registered as competent for this subject
Searched again on 2026-08-25 and it remains the one printed source here that a bibliographic check cannot fix, because it is not a published work with an edition. It is course material issued to participants of a training programme, so there is no catalogue record to verify, no ISBN, and no lawful public copy. Its state stays `registered` for that reason rather than through inattention.
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.
Peer-reviewed literature on cider fermentation microbiology
Various journals · peer-reviewed literature · registered as competent for this subject
Covers the microbial succession of spontaneous cider fermentation, the role of non-Saccharomyces yeasts in the early stages, malolactic conversion by Oenococcus and Lactobacillus species, and the organisms behind the principal spoilage faults.