Juice treatment
Juice pasteurisation
Heat treatment of juice before fermentation, which inactivates enzymes and microorganisms, and in doing so removes the wild flora that would otherwise ferment it.
Also called Flash pasteurisation of juice, Tunnel pasteurisation, Heat treatment of juice.
- Stage
- Juice treatment
- Traditional in
- No single tradition — used wherever it suits
- What it most changes
- Fruit character down, oxidative character down
- Safety
- Carries a safety consideration — see below
Where juice is sold unfermented rather than fermented, pasteurisation is a recognised process control for vegetative pathogens that can be present on fruit, especially where windfalls are used; producers selling unfermented juice should work to the food safety requirements of their own jurisdiction rather than to general practice. Pasteurisation does not remove patulin, which is heat-stable, so it is not a remedy for mould-affected fruit. Operationally, hot juice, steam and hot surfaces present a scald hazard, and glass containers passing through a tunnel can fail on thermal shock, so gradual heating and cooling stages and appropriate guarding matter.
What it is
Pasteurising juice means holding it at a raised temperature long enough to inactivate the organisms and enzymes in it, then cooling it. Two configurations dominate: flash pasteurisation, in which the juice passes continuously through a heat exchanger and is held briefly at a higher temperature before immediate cooling, and tunnel pasteurisation, in which filled and sealed containers pass through a heated tunnel and are treated more slowly at a lower temperature. In cider making the treatment is applied to juice destined for fermentation, to juice sold as juice, and to juice being held before fermentation, and the consequences differ in each case.
Why it is used
- It inactivates polyphenol oxidase, which stops enzymic browning permanently rather than merely inhibiting it as a sulphite addition does.
- It removes the wild yeasts and bacteria present, giving an inoculated fermentation a clean start in which the chosen strain has no competition.
- Where juice is being held before fermentation, or sold as juice, heat treatment is the practical route to a shelf-stable product without relying on sulphite alone.
- For juice sold unfermented it is the recognised process control for vegetative pathogens that may be present on fruit, particularly where windfalls form part of the intake.
How it works
- Heat denatures proteins, which is what inactivates both the enzymes and the organisms: enzyme active sites lose their conformation and microbial membranes and enzyme systems fail.
- Time and temperature trade against one another, so flash treatment at a higher temperature for seconds and tunnel treatment at a lower temperature for minutes can achieve equivalent lethality with quite different effects on flavour.
- Juice proteins that were soluble at ambient temperature denature, aggregate and drop out, which is why pasteurised juice often clears somewhat and why it is less prone to a later protein haze.
- The flavour changes by two mechanisms at once: cooked character is generated by Maillard reactions between reducing sugars and amino compounds and by acid-catalysed dehydration of sugars to furfural, while the fresh volatile esters and aldehydes are simultaneously lost to thermal degradation and to stripping during heating and flash cooling.
- Patulin is heat-stable, so pasteurisation is not a control for it and does not reduce a contaminated juice to a safe one.
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 |
|---|---|---|
| Fruit character | Lowers | Volatile esters and six-carbon aldehydes are thermally labile and are additionally stripped by the heating and cooling steps, so the fresh-fruit top of the aroma is diminished before fermentation begins. |
| Fermentation character | Either way | Removing the wild flora eliminates the non-Saccharomyces contribution of the early ferment, so character depends entirely on the strain subsequently pitched rather than on the fruit’s own population. |
| Oxidative character | Lowers | Permanently inactivating polyphenol oxidase prevents further enzymic browning, so a heated juice resists the colour and aroma changes an untreated juice continues to undergo. |
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
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 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.
Furfural
A toast-and-almond aldehyde formed whenever sugars are heated, arriving in cider either from a toasted barrel or from heat treatment, and a reliable marker of cooked character.
Patulin
A mycotoxin produced by the blue mould that rots stored apples, regulated in apple juice worldwide, and the clearest food-safety reason not to press rotten fruit.
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
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.
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.
Metschnikowia pulcherrima
An early-succession yeast that suppresses competitors by locking up iron, and is used commercially as a controlled non-Saccharomyces partner rather than as a fermenter.
Saccharomyces cerevisiae
The yeast that finishes essentially every cider, whether it arrives in a sachet or from the fruit, the press and the vessel.
What it is done with
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.
Cooked character
A stewed-apple, caramel or jam-like character from heat applied to juice or cider, most often through pasteurisation or hot storage.
Protein haze
A fine haze that forms as protein and tannin combine into insoluble complexes, often appearing in a cider that had already been clear.
Colour loss
A cider left noticeably paler than it should be, usually because fining, filtration or sulphite has removed the phenolic material that gave it colour.
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.
Patulin contamination
Contamination of juice or cider with patulin, a mycotoxin produced by Penicillium expansum in rotting apples — a genuine food-safety question rather than a flavour 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 juice pasteurisation
Heat does several things to juice at once, and separating them is the key to understanding whether the treatment suits a given purpose. It kills the microflora. It denatures polyphenol oxidase, permanently ending enzymic browning in a way that no sulphite addition matches. It denatures soluble protein, which then aggregates and settles, so the juice tends to clear and is less prone to a later protein haze. And it generates flavour that was not there before: Maillard products from reducing sugars reacting with amino compounds, and furfural from acid-catalysed sugar dehydration. The last of these is the price, and how heavily it is paid depends on the time–temperature combination chosen. A brief flash treatment costs relatively little; a long hold at moderate temperature costs a great deal.
The point that is most often glossed over is that pasteurising juice destined for fermentation is a decision about who ferments it. Fresh juice carries a succession of organisms — Hanseniaspora and Kloeckera early, Metschnikowia, then Saccharomyces taking over as ethanol rises — and that succession contributes ester profile, glycerol, and much of what people describe as complexity in wild-fermented cider. Heat removes all of it. That is not an accident of the process to be regretted; it is often the reason for doing it, since a producer working to a consistent specification across many batches cannot afford a variable indigenous population. But a maker who pasteurises and then complains that the cider lacks the character of a traditional ferment has removed the mechanism that would have produced it.
Practice varies by what the producer is actually selling. Large-scale cider production and German juice technology treat pasteurisation as normal, often combined with depectinisation and filtration into a fully specified bright juice. Traditional English, Asturian and Normandy making does not pasteurise juice at all, since the whole method rests on the fruit’s own flora and, in the Normandy case, on native enzyme activity that heat would destroy — pectin methylesterase is denatured along with everything else, so a pasteurised juice cannot be keeved. North American practice is more divided than either, partly because juice sold unfermented is subject to food safety requirements that fermented cider is not, so a producer selling both from the same press run may pasteurise one stream and not the other.
When it goes wrong it usually goes wrong towards cooked character: an over-long hold, a slow cool, or repeated heat treatment of the same juice gives a stewed, caramelised note that fermentation reduces but does not remove. The other frequent error is treating pasteurisation as a general-purpose safety net. It is a control for organisms and enzymes, not for chemical contamination: patulin from rotted fruit survives it intact, and a juice pressed from bad fruit remains a juice pressed from bad fruit after heating. Fruit selection has to be right beforehand.
Related processes
Steps that sit alongside this one, replace it, or depend on it having been done.
Stabilisation
Pasteurisation
Heating cider enough to inactivate the organisms that would spoil it, either in the sealed package or in-line before filling, at a measurable cost in fresh aroma.
Stabilisation
Sterile filtration
Membrane filtration at a rating that retains viable yeast and bacteria, which is what allows a sweet cider to be shelf-stable without heat or preservative — provided the filling that follows is aseptic.
Juice treatment
Juice storage
Holding unfermented juice sound between pressing and fermentation, by chilling, sulphiting, gas blanketing, freezing or aseptic filling.
Juice treatment
Sulphiting
Adding sulphur dioxide to juice to suppress spoilage organisms and oxidative browning, at a level that only means anything once the juice pH is known.
Fermentation
Inoculated fermentation
Starting a ferment by pitching a chosen yeast culture so that one known strain, rather than the fruit’s resident population, does the work.
Juice treatment
Patulin control
Managing the mycotoxin produced by rot fungi in damaged apples, which is controlled by fruit selection rather than by any treatment applied to juice.
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.
- Can you make cider from shop bought apple juice — Yes, provided the juice contains no preservative — check for potassium sorbate or benzoate on the label. Pasteurised juice ferments perfectly well once yeast is added, because pasteurisation removes the organisms but not the sugar.
- How do cider makers keep patulin out — By sorting rotten fruit out before milling, because patulin comes from moulds growing on damaged apples. Fermentation reduces what gets through, so fermented cider carries no limit where juice does.
- Why is sulphite added to cider — Sulphur dioxide suppresses spoilage bacteria and wild yeast before fermentation and protects the finished cider from oxidation. How much of it is active depends strongly on pH, which is why low-acid juice is harder to protect.
- Which yeast ferments cider — Saccharomyces cerevisiae finishes almost every cider fermentation, whether it was pitched or arrived from the press house. In a spontaneous ferment it is not the first organism present, only the one that survives the alcohol it makes.
- How is cider pasteurised
- How long can apple juice sit before i ferment it — Only hours at room temperature before wild fermentation begins. Chilled and sulphited it can be held for a day or two; beyond that it needs freezing, pasteurising or fermenting.
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.
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.
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.
Codex Alimentarius food standards
FAO / WHO · standards body · retrieved 2026-08-24