Pressing
Pomace handling
What is done with the pressed cake once the juice is off it — feed, pectin extraction, composting, digestion or orchard spreading — and why a wet acidic heap beside the press is a problem.
Also called Spent pomace, Press cake, Apple pomace disposal.
- Stage
- Pressing
- Traditional in
- No single tradition — used wherever it suits
- What it most changes
- Not recorded as moving a sensory dimension
- Safety
- None recorded
What it is
Pomace is everything the press did not turn into juice: skin, flesh, core, pips and any stalk that came through the mill, still holding a substantial fraction of its original water. It leaves a batch press as slabs stripped off cloths, a belt or screw press as a continuous scraped stream, and a bladder press as a cake tumbled out of the drum. It is the bulkiest thing a pressing floor produces after the juice itself, and because it is wet, sugary, acidic and already carrying the microflora of the fruit, it starts changing the moment it is set down.
Why it is used
- Every pressing produces it, so having a destination arranged before the season starts is a practical necessity rather than an afterthought.
- It retains real value as stock feed, as a pectin feedstock and as an energy or soil input, so disposal is usually avoidable.
- Left unmanaged next to a working press it becomes a reservoir of acetic acid bacteria and vinegar flies at exactly the point where fresh juice is most exposed.
- Volumes are large enough that waste disposal costs, and in many jurisdictions waste regulation, apply if it is simply thrown away.
How it works
- Fresh pomace is a moist substrate with residual sugar at fruit pH, which is close to ideal for yeasts and then for acetic acid bacteria; fermentation and acetification begin within hours in warm weather and generate heat and volatile acidity.
- That volatile acetic and ethyl acetate signature is precisely the attractant Drosophila species orient to, so a warm heap builds a fly population that then moves onto open juice, press cloths and vessel headspaces nearby.
- Commercial pectin extraction depends on the cell-wall polysaccharide surviving intact, which is why pectin-grade pomace must come from fruit that has not been enzyme-treated and must be dried quickly before its own enzymes and microbes degrade the pectin.
- Composted or spread on land, the cake returns organic matter and potassium to the soil, but the same rapid acidification means fresh pomace applied in a thick layer goes anaerobic and sours rather than breaking down aerobically.
- In anaerobic digestion the residual sugars and soluble solids are the readily degradable fraction that yields biogas, while the fibrous skin and pip material contributes far more slowly.
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.
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.
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.
Malic acid
The acid of apples, which supplies almost all the sharpness a cider has and, through pH, decides how vulnerable that cider is to everything that could spoil it.
What it is done with
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.
Elevators, conveyors and hoppers
Fruit moves by gravity where the building allows it and by flume, belt, bucket elevator or auger where it does not; each method bruises the fruit to a different degree, and each is a machine capable of drawing a person into it.
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.
Vinegar fly contamination
Small flies carrying acetic acid bacteria and spoilage yeasts directly into juice and cider, and depositing them wherever they land.
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.
More on pomace handling
The oldest destination is livestock, and it is still the commonest at farm scale: fresh pomace is fed out to cattle, sheep or pigs, either directly during pressing or ensiled for later. The constraints are real ones rather than folklore. It is a low-protein, high-fibre feed that supplements rather than replaces a ration, it spoils quickly once out of the press, and it retains alcohol if it has begun to ferment, so quantity and freshness both matter. Where fruit has been treated in the orchard, or where the crop included substantially rotten material, the same questions about residues and mycotoxins that apply to the juice apply to the cake.
Industrially, pomace is a raw material rather than a residue. Dried apple pomace is a principal feedstock for commercial pectin, and it is also processed for dietary fibre and polyphenol extracts; that route requires the pomace to be dried promptly and to have come from fruit whose pectin was not deliberately degraded, which puts it in direct conflict with the enzyme treatment that continuous pressing relies on. A large press house therefore chooses its pressing route and its pomace route together. Where no processor is within economic reach, anaerobic digestion and composting are the usual alternatives, and returning composted pomace to the orchard closes a loop that spreading fresh cake does not.
The failure that concerns a cider maker most is not disposal cost but proximity. A wet acidic heap outside the press house door is a culture of acetic acid bacteria and a breeding site for vinegar flies within a day or two of warm weather, and both travel indoors on air and on people. Any pressing floor that has ever had an unexplained volatile acidity problem should look at where its cake goes first. The workable answers are unglamorous: move it out daily rather than accumulating it, keep it away from the doors and from anything open, and do not let the previous day’s pomace sit while the next day’s pressing runs. Where a second pressing is intended, the same clock applies with less slack, because the cake is being kept deliberately rather than removed.
Related processes
Steps that sit alongside this one, replace it, or depend on it having been done.
Pressing
Second pressing and watering
Re-wetting spent pomace and pressing it again to recover a weak second juice — historically the drink of the farm household, and the practice that minimum-juice-content rules now constrain.
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
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
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.
Orchard
Orchard nutrition
Deciding what the trees are fed and how much, a balance in which too little nitrogen shows up as a difficult fermentation and too much shows up as canker and soft growth.
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.
- 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.
- What is malic acid and why does it matter in cider — Malic acid is the acid of apples and supplies almost all the sharpness a cider has. It also sets pH, which decides how well sulphite works and how exposed the cider is to spoilage, so it does far more work than its taste suggests.
- 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 does pectin do in cider — Pectin is the structural polysaccharide that holds fruit cells together. In juice it holds haze in suspension, and it is the molecule keeving depends on: strip its methyl groups and it will gel with calcium and float the nutrients out of the juice.
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.
Hochschule Geisenheim University — beverage technology
Hochschule Geisenheim · university · retrieved 2026-08-24
German beverage-technology research covering apple wine and fruit juice processing, including the enzymology of clarification.