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.
Also called Tunnel pasteurisation, Flash pasteurisation, Thermal stabilisation, Heat treatment.
- Stage
- Stabilisation
- Traditional in
- No single tradition — used wherever it suits
- What it most changes
- Freshness down, fruit character down
- Safety
- Carries a safety consideration — see below
Heating sealed glass generates over-pressure: the liquid expands, dissolved carbon dioxide comes out of solution and the headspace pressure rises, so containers must be rated for the treatment, correctly filled and correctly closed, and a tunnel must be guarded against breakage and flying glass. Hot water sprays, hot containers and hot pipework all present a scald risk. Pasteurisation does not address patulin: the toxin is heat-stable and survives the treatment intact, so control must be exercised at the fruit through sorting and rot exclusion.
What it is
Pasteurisation applies controlled heat for a controlled period so that the microorganisms capable of growing in the product are inactivated. Two arrangements are in general use. Tunnel pasteurisation carries filled and sealed containers through a chamber where they are warmed by water sprays, held, and cooled again, so the treatment happens inside the final package and nothing afterwards can recontaminate it. Flash pasteurisation heats the cider as a flowing stream through a plate exchanger, holds it briefly, cools it just as quickly, and delivers it to a filler — which must then be sterile, because the package is filled after the heat step rather than before it.
Why it is used
- It is the mechanism that makes mass-market sweet and medium cider stable on a shelf: the residual sugar cannot ferment because nothing is left alive to ferment it.
- In the tunnel form the whole sealed package is treated, so it forgives a filling operation that could not be held sterile — the commonest reason a producer chooses heat over membrane filtration.
- It arrests slow spoilage by acid-tolerant lactic acid bacteria and film yeasts in ciders that would otherwise go on changing in trade, which protects a long shelf life and a consistent product.
- It removes the need for a preservative declaration where a producer wants to avoid sorbate or a high sulphite level.
How it works
- Thermal inactivation is a rate process: the fraction of surviving organisms falls with time at a given temperature, and the rate rises steeply as temperature rises. Any treatment is therefore a trade between how hot and how long, and equivalent lethality can be reached along many combinations of the two.
- The design target in fermented cider is the spoilage flora of an acidic alcoholic drink — yeasts including Zygosaccharomyces and Dekkera, and acid-tolerant lactic acid bacteria — not food pathogens. Low pH and ethanol already exclude the vegetative pathogens that unfermented juice must be treated for, which is why juice pasteurisation is designed to a different and more demanding target.
- In a tunnel, lethality accumulates while the container is heating, holding and cooling, and the coldest point in the pack governs the whole. Container size, glass thickness and headspace all change how long that point takes to reach temperature.
- Heat drives off volatile esters and accelerates reactions between sugars and amino compounds, so the treated cider loses fresh fruit aroma and gains a faintly cooked, caramelised note that increases with the severity of the treatment.
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 |
|---|---|---|
| Freshness | Lowers | Fresh apple and pear aroma is carried by volatile esters that are driven off or degraded at pasteurising temperatures, and nothing replaces them. |
| Sweetness | Preserves | Residual and added sugar survives because the organisms that would consume it in the package have been inactivated. |
| Fruit character | Lowers | The same volatiles that read as fresh fruit are the most heat-labile fraction of the aroma, so fruit character falls while cooked and Maillard notes rise. |
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
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.
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.
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.
Glucose
The sugar yeast takes first and the smallest of the three in apple juice, which is why the last sugar left in a slow ferment is almost never glucose.
Fructose
The dominant sugar of apple juice and the sweetest of the common sugars, which is why apple juice tastes sweeter than its total sugar figure implies and why a stuck ferment leaves sweetness behind.
Organisms involved
Zygosaccharomyces bailii
A preservative-resistant spoilage yeast that refements sweetened cider and juice, and one of very few organisms able to grow through sorbate and benzoate at cider strength.
Dekkera bruxellensis
The yeast behind 4-ethylphenol, and the organism that a cider tradition may regard as its signature or its ruin depending on where and how it is made.
Saccharomyces cerevisiae
The yeast that finishes essentially every cider, whether it arrives in a sachet or from the fruit, the press and the vessel.
Lactobacillus collinoides
A lactic acid bacterium first described from cider, and the organism most closely associated with acrolein bitterness through its conversion of glycerol.
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.
What it is done with
Heat exchangers and chilling the juice
A heat exchanger puts two liquids either side of a thin wall so heat crosses and the liquids do not mix; in a cider house the same machine chills warm press juice, holds a tank at temperature, and carries out flash pasteurisation.
Bottling lines and fillers, small and large
Filling is where a finished cider is most exposed: oxygen picked up in the last two minutes can undo a year of care, and carbonated product needs a filler that keeps it under pressure until the closure is on.
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.
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.
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.
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.
Unwanted refermentation
Fermentation restarting in a sealed container, generating carbon dioxide that was not planned for and pressure that a bottle may not withstand.
Microbial haze
Cloudiness caused by a growing population of spoilage organisms, and therefore a symptom of something worse rather than a clarity problem in itself.
Geranium taint
A sharp, unmistakable crushed-geranium-leaf smell produced when lactic acid bacteria metabolise sorbic acid added as a preservative.
Framboise
A raspberry-and-rotten-fruit character with sulphurous overtones, produced by Zymomonas mobilis in sweet ciders that still contain sugar.
Sorbate off-flavour
A faint plastic, candle-wax or celery-like note from sorbic acid used as a preservative, distinct from the geranium taint that bacteria produce from it.
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.
Modern mainstream cider
The industrially produced, consistent, carbonated cider that accounts for most of what is sold worldwide, generally made partly from concentrate and finished to a fixed specification.
Sweet cider
Cider in which sugar is the leading sensation, whether retained from an arrested fermentation, added after it, or produced by keeving.
Medium cider
Cider carrying enough residual or added sugar to be perceptible without dominating, the commonest sweetness level in British retail.
Cidre doux
The sweet tier of the French cider scale, defined since 2025 by a density at or above 1.024 together with an acquired strength no greater than 3% vol, so that the sweetness is demonstrably unfermented juice sugar.
Fruit cider
Cider with other fruit added as juice, purée or flavouring, a category that now accounts for a large share of the global market and spans a very wide range of practice.
Alcohol-free cider
A cider-derived drink at or near zero alcohol, distinct from apple juice in having been fermented, and facing the same problem of what replaces the ethanol.
Cider vinegar
Not a cider but its next stage: cider whose ethanol has been oxidised to acetic acid by bacteria, made deliberately as a condiment and arrived at accidentally as a fault.
Low-alcohol cider
Cider at a reduced strength, reached either by removing alcohol from a finished cider or by arranging for less to be produced, with different consequences for flavour.
More on pasteurisation
The most common misunderstanding about pasteurised cider is what the heat is aimed at. In milk or in unfermented apple juice, pasteurisation exists to inactivate pathogens, and the specification is written around organisms that can make people ill. Fermented cider is already hostile to those organisms: the pH is low, ethanol is present, and vegetative pathogens do not survive that combination in any case. The design target is therefore economic rather than public-health — the acid- and alcohol-tolerant spoilage yeasts and lactic acid bacteria that would restart a fermentation in a sweetened cider, throw a haze, or slowly turn it lactic in the trade. This is why a cider treatment is milder than a juice treatment and why the two should never be described as the same operation.
Choosing between the two arrangements is largely a choice about where the risk sits. Tunnel pasteurisation treats the sealed pack, so the filling line does not have to be sterile and any organism introduced during filling is dealt with afterwards; the penalties are a large and energy-hungry machine, the constraint that the container must survive the thermal and pressure cycle, and a treatment whose severity is set by the slowest-heating point in the biggest container. Flash pasteurisation is far gentler on the liquid, because a thin flowing stream heats and cools in seconds rather than minutes, and it treats bulk product before filling — but it then depends entirely on an aseptic filler, exactly as membrane filtration does. Many producers who install flash pasteurisation discover they have bought a filtration-shaped problem with a heat exchanger attached.
What it costs sensorially is not in dispute. The volatile esters that make a young cider smell of fresh fruit are the first thing lost, and reactions between sugars and amino compounds during the hold generate faintly cooked, caramel or baked-apple notes that were not there before. In a bittersweet cider with substantial phenolic structure this is comparatively easy to absorb; in a light, aromatic cider whose whole appeal is fresh fruit aroma it is not, which is one reason producers of aromatic ciders resist heat and accept the discipline of sterile filtration instead. Over-treatment compounds both problems: the cider tastes cooked, the colour dulls, and the shelf life gained beyond the point of stability is worth nothing.
Related processes
Steps that sit alongside this one, replace it, or depend on it having been done.
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.
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.
Stabilisation
Sorbate stabilisation
Adding potassium sorbate to prevent yeast from restarting a fermentation in the package — an inhibitor rather than a killer, and one that must never be used without sulphite.
Packaging
Bottling
Transferring finished cider into glass, where the dominant variable is how much oxygen the liquid picks up in the few seconds it takes to fill and close each bottle.
Storage
Shelf-life management
Establishing how long a cider stays acceptable in its package and setting a durability date that reflects evidence rather than convention.
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.
- How long does cider last — An unopened commercial cider is usually at its finest within a year of packaging, and filtered, pasteurised products carry a stated date. Strong, tannic, bottle-conditioned ciders can improve for several years.
- 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.
- How do i sweeten cider without it fermenting again — Either remove or kill the yeast — sterile filtration or pasteurisation — or use a non-fermentable sweetener. Sorbate alone is not enough: it prevents yeast multiplying but does not kill what is already there, and needs sulphite alongside it.
- 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.
- What is brettanomyces — *Brettanomyces*, correctly *Dekkera* in its spore-forming form, is a slow yeast that ferments sugars other strains leave behind and produces volatile phenols smelling of farmyard, leather or sticking plaster. In cider it is common and not always unwanted.
- What is sweet cider in america — In the United States and Canada, sweet cider means fresh, unfermented, usually unfiltered apple juice, with no alcohol in it. In Britain the same phrase means a fermented cider with residual sugar.
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.
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.
European Food Safety Authority scientific opinions
EFSA · regulator · retrieved 2026-08-24
Registered for the food-safety questions cider genuinely raises: patulin in juice from rotten fruit, sulphite sensitivity, and the toxicology behind additive limits.