Pressing
Twin-screw pressing
Continuous pressing in which an auger drives pomace along a perforated barrel against a restriction, extracting juice under high shear and compaction.
Also called Screw press (continuous), Auger press, Decanter screw press.
- Stage
- Pressing
- Traditional in
- No single tradition — used wherever it suits
- What it most changes
- Phenolic character up, bitterness up
- Safety
- None recorded
What it is
Not to be confused with the hand-turned screw of a farm press, a continuous screw press uses one or two rotating augers inside a perforated barrel or screen. The flight of the auger conveys pomace forward while the free volume ahead of it is progressively reduced — by a decreasing pitch, a tapering shaft, or a cone or choke plate at the discharge — so material is squeezed as it travels. Juice escapes radially through the screen; the compacted cake extrudes past the restriction at the far end. Twin-screw configurations intermesh two augers, which self-clean the flights and handle fibrous material that would pack solid around a single screw.
Why it is used
- Volume per unit of floor space and per operator is high, and the machine runs continuously without the dead time of loading and stripping a batch.
- It handles difficult feedstock — fibrous perry pear pomace, poorly milled fruit, material with stalk and skin content — that would blind a cloth or a belt.
- The discharge restriction is adjustable, so the trade-off between recovery and cake dryness can be tuned during a run rather than fixed by the equipment.
- It works acceptably on pomace that has not been enzyme-treated, which a belt press does not.
How it works
- Reduction of free volume along the barrel imposes an axial compaction gradient: each element of pomace is at higher pressure than it was a moment earlier, and juice is squeezed out of the shrinking pore space through the screen.
- The auger is simultaneously conveying and compressing, so the pomace is being sheared against the barrel wall and against the flight faces while it is under load — a fundamentally different mechanical history from the pure compression of a batch press.
- That shear tears cell walls and skin tissue, releasing intracellular and wall-bound material that compressive pressing alone leaves in the cake.
- Back-pressure at the discharge choke sets the residence time and the terminal compaction; opening it raises throughput and leaves the cake wetter, closing it dries the cake and raises the extracted solids load in the juice.
- Mechanical work is dissipated as heat, so juice leaving a hard-running screw press is warmer than it went in, which accelerates both enzymatic and non-enzymatic reactions in it.
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 |
|---|---|---|
| Phenolic character | Raises | Shear against the barrel and flights disrupts skin and cell-wall tissue, liberating wall-bound flavanols and hydroxycinnamic acids that compressive pressing leaves behind. |
| Bitterness | Raises | The additional extraction is weighted towards lower-molecular-weight flavanols such as epicatechin and short procyanidin oligomers, which are perceived as bitter rather than drying. |
| Astringency | Raises | Larger polymerised procyanidins released from disrupted tissue bind salivary proteins readily, so the juice arrives with a tactile grip the free run does not have. |
| Oxidative character | Raises | High phenolic substrate levels, entrained air and the frictional heat generated by the auger together speed enzymatic browning in the juice as it leaves the machine. |
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
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.
Procyanidins
The condensed tannins of cider fruit, whose chain length — not their quantity — decides whether the mouth registers bitterness or astringency.
Epicatechin
The flavan-3-ol that apple procyanidins are almost entirely built from, and the most bitter of the phenolic monomers a cider contains.
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.
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.
What it is done with
The continuous screw press
A tapering auger turning inside a perforated cage that conveys mash forward while progressively reducing its volume, forcing juice out through the screen; high throughput and high shear, usually reserved for volume and for second pressings.
Press types compared
A side-by-side account of how the common press types differ in yield, in oxygen exposure, in the phenolic load they put into the juice, in labour and in what they demand of the mill.
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.
Excessive bitterness
Bitterness that dominates the palate rather than supporting it, usually from a blend weighted too heavily towards high-tannin fruit or extracted too hard.
Excessive astringency
A drying, roughening, mouth-puckering sensation that outstays its welcome, produced by larger phenolic polymers precipitating salivary proteins.
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.
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 twin-screw pressing
The distinguishing feature of a continuous screw press is shear, and shear is what makes its juice different. A pack or membrane press separates phases: it drains liquid out of a solid matrix. An auger press does that too, but it also grinds. Skin, seed coat, core fragment and cortical tissue are worked against metal under pressure, and the juice that comes off carries a substantially higher load of fine solids and of phenolic material that was bound in cell walls rather than dissolved in the vacuolar sap. Bitterness and astringency both rise, the colour is darker, and the juice is turbid enough that clarification is not optional.
That makes it a poor choice for anything where juice character is the product, and a reasonable one where it is not. Screw presses are found in bulk juice and concentrate operations, in second-pass recovery from cake that a primary press has already worked, and in some perry-pear handling, where the fibrous stone-cell tissue of a perry pear defeats gentler machines. They are also used where the cake matters: a screw press leaves a drier pomace than a batch press, which reduces the volume and weight going to disposal or feed and makes the residue easier to handle.
What the operator actually manages is the choke setting against the feed rate, and the honest description of that decision is that it trades juice quality for recovery in both directions at once. Tightening the restriction wins volume and dries the cake, but at the cost of more heat, more shear, more extracted solids and a coarser phenolic profile. Because that cost lands squarely on the sensory result, twin-screw pressing sits at the volume-over-clarity end of pressing choices — which is a legitimate position for a producer whose juice will be enzymatically clarified, filtered and blended, and the wrong one for a maker whose fermentation is meant to do the clarifying itself.
Related processes
Steps that sit alongside this one, replace it, or depend on it having been done.
Pressing
Belt pressing
Continuous pressing in which enzyme-treated pomace is carried between two converging porous belts and progressively dewatered around a series of rollers.
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.
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.
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.
Juice treatment
Juice clarification
The deliberate use of enzyme, fining agents or mechanical separation to produce a bright juice before fermentation, and what that costs the ferment.
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 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.
- Which type of cider press should i use — No press is best. Each one sits at a different point on four trade-offs: how much juice it recovers, how much air the juice meets, how hard it works the solids, and how much labour and capital it needs.
- 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.
- 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.
- What is oxidation in cider
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.