Fruit preparation
Pomace conditioning
Letting milled pomace stand before it goes to the press so that it drains better, presses faster and gives more juice.
Also called Mash resting, Pomace resting, Standing the pomace.
- Stage
- Fruit preparation
- Traditional in
- Normandy, Pays d’Auge
- What it most changes
- Astringency down, oxidative character up
- Safety
- None recorded
What it is
A short, deliberate rest between the mill and the press — from a few minutes in a hopper to a few hours in a tank — during which nothing is added and nothing is removed, but the physical character of the pomace changes. The mass loosens, free juice appears and begins to drain, and the pomace stops behaving like wet sawdust and starts behaving like something a press can work. Most operations do it without naming it, because the pomace has to wait for the press anyway; the distinction between accidental and deliberate conditioning is whether the maker chose the interval and the temperature.
Why it is used
- Freshly milled pomace is a dense, sticky mass that resists drainage, and pressing it immediately produces a slow, high-pressure cycle with juice trapped in the cake.
- A rest lets free juice separate and form channels through the mass, so the press works with the pomace instead of against it and cycle times shorten.
- Where a maker wants the softer, less astringent phenolic profile that partial pre-press oxidation gives, the rest is when that oxidation happens.
- A short hold evens out the mismatch between a mill running continuously and a press working in batches, which is a real constraint in any operation with more than one press cycle a day.
How it works
- Milling ruptures cells and releases their contents; the rest allows the released juice to migrate out of the disrupted tissue under gravity and capillary action rather than being forced out under pressure.
- The fruit’s own pectin methylesterase continues to act on cell-wall pectin, and partial de-esterification reduces the water-holding capacity of the mass so it releases juice more readily.
- Polyphenol oxidase, brought into contact with hydroxycinnamic acids and procyanidins by milling, oxidises them to quinones which then couple and polymerise; much of the resulting material is bound in the pomace and leaves with the cake rather than entering the juice.
- Warmth accelerates all of this and also accelerates the growth of Acetobacter, Gluconobacter and wild yeasts already on the fruit, so the same rest that improves the press run also starts a fermentation and an acetification the maker has not chosen.
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 |
|---|---|---|
| Astringency | Lowers | Quinone-mediated coupling converts soluble procyanidins into larger polymers that bind to cell-wall material and leave with the pomace, so less of the protein-precipitating fraction reaches the juice. |
| Oxidative character | Raises | Enzymic oxidation in the pomace consumes oxygen and generates quinones before the juice ever sees a vessel, so the resulting cider carries an oxidised phenolic signature laid down before fermentation. |
| Body | Either way | A longer rest extracts more soluble pectin and cell-wall polysaccharide into the juice, which adds colloidal weight, while the same rest removes phenolic material that would also have contributed structure. |
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
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.
Pectin methylesterase
The enzyme that strips methyl groups from pectin, exposing the charged sites that calcium bridges — which is the reaction the whole of keeving is built on.
Polyphenol oxidase
The copper enzyme that turns cut apple brown within seconds, and the reason a cidermaker has to decide, at the press, whether to let the juice oxidise or to stop it.
Procyanidins
The condensed tannins of cider fruit, whose chain length — not their quantity — decides whether the mouth registers bitterness or astringency.
Total phenolics
The single number used to summarise everything phenolic in a juice, useful for comparing fruit and misleading whenever it is used to predict how a cider will taste.
Galacturonic acid
The sugar acid that pectin chains are built from, released as they break down, and a significant part of why juice from rotten fruit binds so much of the sulphite added to it.
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.
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.
Hanseniaspora uvarum
The apiculate yeast most often reported from grapes and widely present on apples too, whose anamorph name Kloeckera apiculata still appears throughout older cider literature.
Kloeckera apiculata
The anamorph name for Hanseniaspora uvarum, still in wide use in cider writing, and often used loosely as a collective term for all apiculate yeasts.
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
Particle size, yield and phenolic extraction
Milling finer raises the juice that can theoretically be extracted and the phenolic load carried into it, but past a point the pomace stops draining and yield collapses — so the right particle size is set by the press, not by the mill.
The pomace belt, and what becomes of pomace
Pressed cake leaves a modern press on a belt or an auger and goes to stock feed, to land, to anaerobic digestion or to pectin extraction; on a farm it usually goes to cattle or back on the orchard, and neither is as simple as it is usually described.
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.
Enzymatic browning
The rapid darkening of milled fruit and fresh juice as polyphenol oxidase converts phenolics to quinones, taking colour and some tannin structure with it.
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.
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.
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.
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.
More on pomace conditioning
The boundary with maceration is one of intent and duration rather than a bright line, and it is worth being explicit about it. Conditioning is a technological rest aimed at how the pomace behaves in the press: the maker wants drainage, yield and a manageable cake, and any phenolic change is a side effect to be tolerated or mildly exploited. Maceration is an extraction step, held longer and often temperature-managed, in which the objective is to pull phenolics, colour and aroma precursors out of the skins and into the juice. The same tank can be doing either depending on why it is being used and for how long, and a rest that begins as conditioning becomes maceration if it is extended with extraction in mind. Where this record describes conditioning, it means the short pre-press interval, not the long contact.
Practice varies with tradition and with what the phenolics are for. French cider making has long accepted, and in places sought, a degree of oxidation in the pomace and in the juice; the characteristic softness of a well-made cidre owes something to phenolic material that has been oxidised and removed before fermentation rather than left to assert itself in the glass. English rack-and-cloth practice on bittersweet fruit tends to the same result by the same route, simply because building a cheese takes time and the pomace oxidises while it waits. By contrast, a maker working with fresh, low-tannin fruit for an aromatic modern style has every reason to keep the interval short and the temperature low, because the same oxidation that mellows a bittersweet strips the delicate esters that style depends on, and there is little tannin to soften in the first place.
The failure is letting the rest run. Pomace is a warm, sugary, aerobic, heavily inoculated substrate, and a mass left standing overnight in a mild autumn does not merely oxidise — it ferments at the surface, acetifies where air reaches it, and attracts vinegar flies which move acetic acid bacteria through the rest of it. The result reaches the press as juice already carrying volatile acidity and ethyl acetate that no later treatment will remove. The other error is uneven conditioning: a hopper drawn down from the bottom means the pomace at the top has stood for hours while the pomace at the bottom has stood for minutes, so the press receives a mixture whose behaviour and phenolic state vary through the cycle.
Related processes
Steps that sit alongside this one, replace it, or depend on it having been done.
Fruit preparation
Milling
Reducing whole fruit to a pulp so that the press has cell walls it can drain, rather than intact apples it can only bruise.
Fruit preparation
Maceration
Holding milled pomace before pressing so that phenolics, aroma precursors and pectin have time to move out of the solid tissue and into the juice.
Fruit preparation
Enzyme addition to pomace
Dosing pectin-degrading enzyme into milled pomace rather than into juice, to raise press yield and change how the cake drains.
Pressing
Pressing yield
The proportion of a fruit charge recovered as juice, and why a single headline figure for it is not a meaningful number.
Juice treatment
Juice oxidation
The enzymic browning that begins the moment apple juice meets air, which some traditions deliberately allow and others suppress.
Pressing
Rack-and-cloth pressing
Building pomace into thin cloth-wrapped layers separated by racks, so that juice has a short path out and the stack can carry the pressure needed to force it.
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 are apples pressed for cider — The fruit is first milled to a pulp, then that pulp is squeezed — traditionally in cloth-wrapped layers under a screw or hydraulic ram, and industrially in a belt or bladder press. Whole apples cannot be pressed usefully; they must be broken first.
- How are apples milled for cider
- What is pressing yield — Pressing yield is the proportion of fruit weight recovered as juice. It varies from under half on a poorly loaded basket press to around seventy per cent on a well-run rack-and-cloth or belt press.
- 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.
- 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.
- What are procyanidins in cider — They are the condensed tannins of apples: chains of catechin-type units whose length decides how much of the phenolic load reads as bitterness and how much as astringency. Two ciders with identical total tannin can taste nothing alike.
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 Science of Cidermaking and associated technical writing
Andrew Lea · reference work · passage verified 2026-08-24
Written by a food chemist who worked at Long Ashton on apple phenolics. Unusual among specialist cider writing in that it is primary-research-adjacent: the author is describing work he did, and cites the literature. This is why it is registered at tier 1 for chemistry while a general cider book is not.
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.
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.