Fault
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.
Also called colloidal haze, protein-tannin haze.
- Severity
- Cosmetic — looks wrong, tastes fine
- Where it starts
- Juice treatment, Stabilisation, Storage, Maturation, Fermentation
- Can it be fixed?
- Yes, if caught in time
- When you notice it
- Maturation, Stabilisation, Storage
- Signs
- 5 recorded
What it is
Protein haze arises when soluble proteins carried over from the fruit associate with phenolic compounds to form particles large enough to scatter light. Its characteristic behaviour is delayed appearance: a cider bottled bright develops a haze weeks or months later, often after a change in temperature. In cider it is less prominent than in beer or white wine, because cider’s phenolic content tends to remove much of the protein during fermentation, but it occurs and it is a common cause of the bright-then-hazy pattern.
What you notice
Grouped by sense, because that is how the fault presents itself rather than how it works.
To look at
- A fine haze appearing in a cider that was clear when bottled
- A light, powdery deposit rather than a compact yeast sediment
How the batch behaves
- Haze that comes and goes with temperature, worse when cold — Chill haze that clears on warming is the classic protein signature.
- A sample that clears when heated and rehazes on cooling
On the palate
- A slightly dulled, softer palate as tannin is removed with the protein
When it appears. Often only on chilling, and often only after packaging — which is why it is so commonly discovered by a customer rather than in the cellar.
The chill-and-warm test is diagnostic and costs nothing, and it is also the test that predicts whether a cider will haze in a customer’s fridge — which is the practical question behind the fault.
Hochschule Geisenheim, Peter Mitchell / Cider and Perry Academy
What it is mistaken for, and how to tell
One observation per rival, chosen because it separates them rather than because it describes either. Several of these are not faults at all — a style feature, a normal outcome, or the fruit behaving as it does.
- Pectin haze — Chill a sample hard and then let it warm. A protein haze appears and then clears; a pectin haze does neither.
- Metal haze — A metal haze usually comes with a metallic note on the palate and a history of contact with the wrong alloy.
- Microbial haze — A protein haze is stable and odourless; a microbial one increases and brings a smell with it.
What is actually happening
The chemistry or microbiology behind it. Understanding the mechanism is what makes the prevention make sense rather than being a list of rules.
Proteins from the fruit survive pressing and fermentation in small quantities. Under cider conditions they carry a net positive charge, since the pH is well below their isoelectric points, and they associate with negatively charged phenolic material — principally the procyanidins — through hydrogen bonding and hydrophobic interaction.
The complexes formed are initially small enough to stay dispersed, and grow over time until they scatter light. Growth is accelerated by temperature change, by agitation and by slow oxidation of the phenolics, which increases their capacity to bind protein. This is why the haze appears late and why chilling makes it worse.
The same reaction is the basis of tannin fining and of protein fining, used deliberately. Gelatin, isinglass and other proteinaceous finings are added to precipitate excess tannin; bentonite, a clay, adsorbs positively charged protein and removes it. Which one is appropriate depends on which component is in excess, and using the wrong one makes the cider worse.
Traditional cider is less prone than white wine, because the high phenolic content of cider fruit removes most of the available protein during fermentation and settling. Ciders made from low-tannin dessert fruit, or those with added protein-based fining that was overdosed and not fully removed, are more exposed.
How it happens
| Cause | Stage | How often |
|---|---|---|
| Temperature swings in storage, driving complex formation | Storage | common |
| Protein carried through from the fruit and not removed during settling | Juice treatment | occasional |
| Over-fining with a proteinaceous agent, leaving unreacted protein in the ciderThe commonest avoidable cause: fining without a bench trial can leave more protein than it removes. | Stabilisation | occasional |
| Slow oxidation of phenolics increasing their protein-binding capacity | Maturation | occasional |
| A low-tannin cider in which the protein was never precipitated during fermentation | Fermentation | occasional |
Can it be put right?
Most cider faults cannot be reversed. Where that is the answer it is given plainly — an honest 'this batch is what it is' is more useful than a procedure that will not work.
| Option | Effectiveness | What it involves |
|---|---|---|
| Accept the haze | Reliable | It has no effect on flavour beyond a slight softening, and an unfiltered cider is not expected to be brilliant. |
| Fine with an adsorbent clay such as bentonite | Partial | The standard treatment for excess protein, and effective. It also strips some aroma, so bench trial and use the smallest effective dose from the supplier’s guidance. |
| Chill the cider to force the haze out, then rack or filter | Partial | Cold stabilisation precipitates the complexes so they can be removed before packaging. Requires the ability to hold the cider cold for a period. |
| Filter the finished cider | Partial | Removes the haze present. Does not stop further complexes forming from the protein and tannin still in solution, so a bottled cider can rehaze. |
| Wait for it to clear | Unlikely to work | The complexes settle very slowly and continue to form. Time alone rarely produces a bright cider. |
CiderHQ gives no additive dosage figures. An addition is a food-safety decision that depends on legal limits, on the juice in front of you and on what you are protecting against, and the right figure comes from your supplier’s or regulator’s own guidance rather than from a general reference.
Preventing it
- Allow proper juice settling and racking before fermentation, which removes much of the protein along with the gross solids.
- Bench trial any fining before treating a batch, with a range of doses, and choose the smallest that works.
- Match the fining agent to the problem: an adsorbent clay for excess protein, a protein fining for excess tannin.
- Cold-stabilise before bottling where the cider will be sold or stored cold, so the haze forms in the tank rather than in the bottle.
- Store finished cider at a stable temperature rather than moving it between warm and cold.
Protein haze is defined more by its timing than by its appearance. Almost every haze looks alike; this is the one that was not there at bottling and is there three months later, and it is the one that responds to temperature.
Its most common cause in small-scale production is over-fining, which is an unfortunate irony: a treatment applied to make cider clear leaves behind material that makes it cloudy. The remedy is the bench trial that is so often skipped — a row of samples at different doses, left for a day, and the smallest effective one chosen.
Cider is somewhat protected by its own chemistry. A traditional bittersweet cider carries so much phenolic material that most of the protein is precipitated long before packaging, and protein haze is more a problem of low-tannin ciders made from dessert or culinary fruit.
It is worth keeping in perspective. Nothing about a protein haze indicates spoilage, and the drink is unchanged apart from a faint softening where the complexes have taken some tannin with them. The reason to deal with it is presentation, and the reason not to is that every treatment for it removes something else as well.
The compounds involved
Tannin–protein complexes
What astringency physically is: long tannin chains cross-linking salivary proteins and precipitating them, which is also the mechanism behind fining, protein haze and the classic cider-and-cheese pairing.
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.
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.
Amino acids
The largest usable nitrogen fraction in apple juice, and the raw material from which yeast builds both its own protein and most of the aroma compounds a cider carries.
Where in the process it arises
Fining
Adding a reactive agent that binds a target colloid and carries it to the bottom, chosen according to whether the problem is tannin, protein or a phenolic taste fault.
Juice settling
Letting freshly pressed juice stand cold and undisturbed so that gross solids fall, then racking the cleaner juice off the deposit before pitching.
Cold stabilisation
Holding cider cold before packaging so that anything which would fall out of solution in a cold warehouse falls out in the tank instead.
Filtration
Passing cider through a porous medium to reach a stated visual brightness, at a real cost in colloidal material, body and aroma.
Bench blending trials
Making small measured mixtures of candidate lots and tasting them before committing tanks, because how components behave together cannot be worked out from how they taste apart.
Faults it is confused with
These present similarly. What separates them is set out on each page.
Pectin haze
A persistent, slightly viscous haze that will not settle, caused by pectin from the fruit remaining in solution as a colloid.
Metal haze
A haze or dark cast caused by dissolved iron or copper picked up from equipment, forming insoluble complexes with phosphate or with the cider’s phenolics.
Yeast haze
Cloudiness from yeast cells that have not settled out, usually because the strain flocculates poorly or the cider has not been left alone long enough.
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.
Where this comes up in a guide
The link lands on the step where the fault arises rather than at the top of the pathway, because that is where the decision that causes it is taken.
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.
- Is cider vegan — Cider itself is a plant product, but some producers clarify it with animal-derived finings such as gelatine, isinglass or chitosan. Vegan status therefore depends on the fining regime, which is why some ciders are certified and others are not.
- How do i clear a cloudy cider
- 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.
- Do i need a filter to make cider
- Does cider contain antioxidants — Cider carries apple polyphenols, and tannic bittersweet ciders carry considerably more than pale ones made from dessert fruit. What that means for health is a clinical question this site does not adjudicate.
- Why does tannic cider feel drying rather than bitter — Because astringency is a physical event rather than a taste. Tannin cross-links the proteins that lubricate the mouth, and the loss of lubrication is what registers as drying; bitterness is a separate receptor event happening at the same time.
Where to go next
- The fault finder — Describe what you can smell and see, and narrow it down from the signs.
- All faults — Grouped by where they come from and how serious they are.
- Cider science — The chemistry and microbiology these faults come out of.
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.
Peer-reviewed literature on apple phenolics and cider sensory perception
Various journals · peer-reviewed literature · registered as competent for this subject
Registered as a class rather than as one paper, because the mechanisms CiderHQ describes — tannin chain length driving the split between bitterness and astringency, salivary protein precipitation, enzymatic browning — are established across many studies rather than resting on any single one. Individual papers are cited where a specific number is quoted.
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.