Practical
Cider faults
What has gone wrong, what caused it, and what can be done about it — which, for most of these, does not include putting it back.
Most cider faults cannot be reversed. On 35 of the 52 records here, the thing a reader would try first — taking the fault back out of the drink — is recorded as not possible: the compound is already formed, the organism has already done what it does, and no treatment puts the batch back. Across all 52 of them CiderHQ lists 244 corrective options, of which 38 cannot be done at all and a further 46 are unlikely to work. That is stated plainly rather than softened, because an honest “this batch is what it is” is more useful than a procedure that will not work and costs a weekend.
The value of this section is therefore not repair. It is understanding why a fault happened, which is the only thing that prevents the next batch from repeating it. Every record sets out the chemistry or microbiology involved, the causes with the stage each originates at and how often it is the real explanation, and what has to change upstream. A fault understood at the level of mechanism is one you can design against; a fault known only by its name is one you meet again.
A small number of these are not quality problems at all. 5 carry a genuine hazard — over-pressurised glass above all — and those are marked below and again at the top of their own pages, before any chemistry. If you are holding a bulging or gushing bottle, read the safety note before you do anything else with it.
The fault finder takes the signs you can actually observe — what it smells of, what it looks like, how the bottles are behaving — and returns the candidates in order with what separates them. It ranks rather than diagnoses, because several faults share signs and a tool that gave one confident answer would be wrong a good part of the time.
Described in full
- Layout
- Three parallel columns, each running downwards: the condition, the organism or reaction it permits, the faults that follow, and the practice that prevents it.
- Oxygen
- Air in a part-empty vessel or at every transfer. It permits acetic acid bacteria to work, and it drives chemical oxidation of phenolics independently of any organism.
- What oxygen produces
- Volatile acidity and, at higher concentration, frank acetification — cider turning to vinegar. Alongside it, oxidation gives sherry, walnut, bruised-apple and cardboard notes as acetaldehyde and browning products accumulate.
- Wild organisms
- Present on the fruit and in old wood. Brettanomyces and certain lactic bacteria decarboxylate hydroxycinnamic acids to volatile phenols; some lactic bacteria also form the tetrahydropyridines behind mousiness.
- What wild organisms produce
- Phenolic character — leather, smoke, sticking plaster — which is a signature at low levels and a fault above them. Mousiness is not detectable on the nose and appears only as a lingering aftertaste, which is why it is so often missed.
- Residual sugar
- Any fermentable sugar left in a sealed container is a fuel supply for whatever yeast survives filtration or arrives afterwards.
- What residual sugar produces
- Refermentation in the bottle, and with it over-carbonation, gushing on opening and, in the worst case, a bottle that fails under pressure. This is a safety matter, not only a quality one.
- Prevention
- Keep vessels full and cool, and minimise transfers, for oxygen. Sulphite and sanitation for wild organisms. For residual sugar, either stabilise and filter, or leave the cider genuinely dry — the only condition that cannot referment is one with nothing left to ferment.
By how serious it is
Safety first. A cosmetic fault and a pressure hazard are not the same kind of problem, and sorting them alphabetically would imply that they are.
Safety — there is a real hazard here (4)
These are not quality problems. Over-pressurised glass injures people, and the guidance on these pages comes before any account of the chemistry.
Hazard
Bottle over-carbonation
More dissolved carbon dioxide in the bottle than intended or than the glass is rated for — a presentation problem at the mild end and a physical hazard at the severe one.
Hazard
Unwanted refermentation
Fermentation restarting in a sealed container, generating carbon dioxide that was not planned for and pressure that a bottle may not withstand.
Hazard
Gushing
Cider that erupts from the bottle on opening, either because it is over-pressurised or because something in it is nucleating the dissolved gas violently.
Hazard
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.
Serious — the batch may not be salvageable (14)
The drink is substantially altered and, in most of these, permanently. The page will say which.
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.
Hazard
Stuck fermentation
A fermentation that has stopped before the sugar is gone and will not restart, leaving a sweet, low-alcohol cider that is vulnerable to everything.
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.
Safety note
Excess sulphur dioxide
A struck-match or burnt-match aroma and a prickle at the back of the nose from too much free sulphur dioxide, with a real health consideration for sulphite-sensitive people.
Film yeast growth
A pale, powdery or wrinkled film of aerobic yeast growing on the surface of a standing cider, consuming alcohol and acid and producing acetaldehyde.
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.
Safety note
Mould taint
Musty, earthy, cellar-damp or rotten-fruit character carried in from mouldy fruit or from mouldy equipment, and a marker that the patulin question needs asking.
Mousiness
A retronasal taint of mouse cage, stale popcorn or crackers that appears only after swallowing — and that a substantial fraction of people cannot detect at all.
Vinegar fly contamination
Small flies carrying acetic acid bacteria and spoilage yeasts directly into juice and cider, and depositing them wherever they land.
Acrolein bitterness
An intense, lingering bitterness quite unlike tannin, produced when lactic acid bacteria convert glycerol to acrolein and the acrolein reacts with the cider’s phenolics.
Geranium taint
A sharp, unmistakable crushed-geranium-leaf smell produced when lactic acid bacteria metabolise sorbic acid added as a preservative.
Mercaptan taint
Onion, garlic, burnt rubber and cooked-cabbage aromas from thiols and disulphides formed when hydrogen sulphide is left in cider long enough to react onwards.
Framboise
A raspberry-and-rotten-fruit character with sulphurous overtones, produced by Zymomonas mobilis in sweet ciders that still contain sugar.
Smoke taint
Ashtray, burnt and medicinal character in cider made from fruit exposed to wildfire smoke, which enters the fruit as bound precursors and is released later.
Quality — the drink is worse for it (27)
Drinkable but diminished. Several of these are also characters that some traditions accept or seek deliberately, and the pages say where that line falls.
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.
Acetaldehyde excess
A bruised-apple, green-nut or sherry aroma from acetaldehyde, produced by oxidation, by film yeast, or left behind by a ferment that was interrupted.
Brettanomyces character
Farmyard, horse-blanket, smoky and sticking-plaster aromas from Brettanomyces yeast converting hydroxycinnamic acids into volatile phenols.
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.
Ethyl acetate taint
A solvent, nail-varnish or pear-drop aroma from ethyl acetate, the most abundant ester in cider and the one that turns from lift to fault over a narrow range.
Hydrogen sulphide
A rotten-egg or drain smell from hydrogen sulphide produced by stressed yeast, usually the first visible consequence of a nitrogen-short juice.
Low acidity
A cider without enough acid to give it definition, tasting soft, heavy and dull — and sitting at a pH that leaves it exposed to spoilage organisms.
Nitrogen deficiency character
The set of characters a nitrogen-starved fermentation produces together — sulphide, a stalled or dragging ferment, harsh higher alcohols and a thin, hard cider.
Sluggish fermentation
A fermentation that is still moving but far more slowly than it should, extending the period during which the cider is weak, sweet and exposed.
Cooked character
A stewed-apple, caramel or jam-like character from heat applied to juice or cider, most often through pasteurisation or hot storage.
Cork taint
A damp-cardboard, wet-newspaper mustiness from trichloroanisole, usually carried by a natural cork but capable of reaching cider by other routes.
Excess diacetyl
A butter, butterscotch or popcorn character from diacetyl, produced by lactic acid bacteria metabolising citric acid, and by yeast under stress.
Excessive acidity
Acidity high enough to dominate everything else, leaving a cider that is thin, hard and sour rather than fresh.
Excessive astringency
A drying, roughening, mouth-puckering sensation that outstays its welcome, produced by larger phenolic polymers precipitating salivary proteins.
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.
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.
Lactic off-flavours
Sauerkraut, sour milk, silage or cheesy notes from lactic acid bacteria working on sugars and other substrates rather than on malic acid alone.
Light strike
A skunky, cooked-cabbage or drain-like aroma produced when light acting on riboflavin generates sulphur compounds in a bottle.
Plastic and packaging taint
Plastic, rubber, adhesive or chemical notes picked up from unsuitable containers, liners, hoses, gaskets or cleaning residues.
Reduction
A closed, stale, slightly sulphurous character in cider held under strongly oxygen-free conditions, sometimes clearing with air and sometimes not.
Ropiness
Cider that pours thick and pulls into an oily thread, caused by lactic acid bacteria secreting long-chain glucan polymers into the drink.
Thin body
A cider with no weight or texture in the mouth, most often from over-watered pomace, low-gravity juice or a blend with nothing to give it substance.
Under-carbonation
A cider intended to sparkle that has little or no dissolved gas, usually because the bottle conditioning never started or the closure did not hold.
Atypical ageing
A cider that loses its fruit unusually early and develops a flat, faintly acrid or naphthalene-like character — a syndrome described in white wine and less firmly established in cider.
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.
Metallic taint
A metallic, inky or blood-like taste from dissolved iron, copper or zinc picked up from equipment, usually accompanied by accelerated oxidation.
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.
Cosmetic — it looks wrong and tastes fine (7)
A haze or a deposit that has no effect on the drink itself. Worth identifying so that it is not treated as something worse.
Pectin haze
A persistent, slightly viscous haze that will not settle, caused by pectin from the fruit remaining in solution as a colloid.
Excessive sediment
More deposit in the bottle or vessel than the presentation intends, ranging from a normal conditioning yeast layer to a loose sludge that clouds every pour.
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.
Starch haze
A persistent haze caused by starch carried in from under-ripe fruit, which has not yet been converted to sugar and stays suspended in the cider.
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.
Pinking
An unexpected pink or salmon tint developing in a pale cider or perry, associated with oxidation of colourless phenolic precursors.
By where it starts
The same fault list, sorted by the stage its causes originate at. This is the ordering that matters for prevention: a problem introduced at harvest is not solved in the cellar, and a fault appears here under every stage that can produce it.
The ones that cannot be undone
Faults whose records include a course of action marked as not possible — almost always the one a reader would try first, which is taking the fault back out of the drink.
Being on this list does not mean nothing can be done. It means the direct repair cannot be done. What is left is usually blending into a much larger sound volume, stabilising the batch so it stops getting worse, or accepting the batch for what it has become — and each page says which of those applies rather than implying that a treatment exists.
- Acetification
- Acrolein bitterness
- Atypical ageing
- Bottle over-carbonation
- Brettanomyces character
- Colour loss
- Cooked character
- Cork taint
- Enzymatic browning
- Ethyl acetate taint
- Excess diacetyl
- Excess sulphur dioxide
- Film yeast growth
- Flat and lifeless
- Framboise
- Geranium taint
- Gushing
- Lactic off-flavours
- Light strike
- Mercaptan taint
- Mould taint
- Mousiness
- Nitrogen deficiency character
- Oxidation
- Patulin contamination
- Pectin haze
- Plastic and packaging taint
- Smoke taint
- Sorbate off-flavour
- Starch haze
- Stuck fermentation
- Under-carbonation
- Unwanted refermentation
- Vinegar fly contamination
- Volatile acidity
Every fault
All recorded faults, alphabetically.
- Acetaldehyde excess
- Acetification
- Acrolein bitterness
- Atypical ageing
- Bottle over-carbonation
- Brettanomyces character
- Colour loss
- Cooked character
- Cork taint
- Enzymatic browning
- Ethyl acetate taint
- Excess diacetyl
- Excess sulphur dioxide
- Excessive acidity
- Excessive astringency
- Excessive bitterness
- Excessive sediment
- Film yeast growth
- Flat and lifeless
- Framboise
- Geranium taint
- Gushing
- Hydrogen sulphide
- Lactic off-flavours
- Light strike
- Low acidity
- Mercaptan taint
- Metal haze
- Metallic taint
- Microbial haze
- Mould taint
- Mousiness
- Nitrogen deficiency character
- Oxidation
- Patulin contamination
- Pectin haze
- Pinking
- Plastic and packaging taint
- Protein haze
- Reduction
- Ropiness
- Sluggish fermentation
- Smoke taint
- Sorbate off-flavour
- Starch haze
- Stuck fermentation
- Thin body
- Under-carbonation
- Unwanted refermentation
- Vinegar fly contamination
- Volatile acidity
- Yeast haze
Next
- The fault finder — describe the signs, get the candidates in order with what distinguishes them.
- Microbiology — the organisms behind most of what goes wrong.
- How cider is made — the stages these faults are introduced at.
- The sensory vocabulary — telling a fault from a character somebody made on purpose.