Science
Cider science
Cider is fruit juice that something lived in. Almost every question about why one tastes different from another resolves, eventually, into a question about what is dissolved in it and what put it there.
This section holds 80 compounds, 39 organisms and 138 sensory descriptors, and it exists to connect them. A compound record that could only give a formula would be a glossary entry; what makes this layer worth building is the chain that runs from a molecule, through the organism or process that makes it, to something a person can taste, smell or measure.
Figures appear only where they can carry their context — the property, the unit, the source and the conditions the measurement was taken under. Where a genuinely useful number has no home in that structure, it is stated in prose with the institute or method named rather than presented as analysis. And nothing here is a recommendation: what a compound does is a fact, what to do about it in your cellar is not.
Described in full
- Layout
- Four rows, one per component. The left column is what is in the pressed juice; an arrow crosses to the right column, which is what is there after fermentation.
- Sugar
- Apple juice carries glucose, fructose and sucrose, with fructose the largest. Nearly all of it becomes ethanol and carbon dioxide; roughly half the sugar mass leaves the vessel as gas.
- Acid
- Malic acid is almost the whole acid content of apple juice. Fermentation itself changes it little. If malolactic fermentation follows, the malic becomes lactic acid, acidity falls and pH rises.
- Phenolics
- Procyanidins extracted from skin and flesh. Fermentation does not create or destroy them so much as rearrange them: chains polymerise, some bind to yeast and precipitate, and the perceived balance shifts from bitterness towards astringency and then softens.
- Nitrogen
- Amino acids and ammonium, together the yeast-assimilable nitrogen. It is consumed almost entirely, converted into yeast biomass. Whatever is left at the end is a food supply for anything that follows.
- Why nitrogen decides the aroma
- Yeast short of nitrogen produces hydrogen sulphide and mercaptans — rotten egg, drains, rubber. Yeast with plenty ferments fast and clean but leaves less of the fruit’s own character. Keeving works precisely by removing nitrogen deliberately.
- What the table omits
- Pectin, sorbitol, potassium and the trace compounds that decide most of the aroma. These four are the ones a cidermaker measures and can act on.
Chemistry — what is actually in the glass
Molecules grouped by where they enter the drink: what the fruit arrives carrying, then what the ferment makes of it, then what a maker adds deliberately. Start here if you want to know what something is, what it does, or what removes it.
3 compounds
Sugars
What the ferment starts with and what a sweet cider still holds.
1 compound
Sugar alcohols
Sweet, and mostly unfermentable — the reason perry behaves differently.
8 compounds
Acids
Sharpness, and the drink’s own microbiological defence.
Acetic acid, Malic acid, Lactic acid, Citric acid, Galacturonic acid and 3 more
17 compounds
Phenolics
Tannin, bitterness, astringency and colour.
Procyanidins, 4-Ethylphenol, Total phenolics, Chlorogenic acid, Epicatechin and 12 more
5 compounds
Polysaccharides
Cloudiness, press behaviour and what keeving acts on.
7 compounds
Nitrogen compounds
Yeast food, and the shortage behind most stuck ferments.
Yeast-assimilable nitrogen, Amino acids, Ammonium nitrogen, Biogenic amines, Ethyl carbamate and 2 more
3 compounds
Enzymes
Catalysts that change the juice without being consumed by it.
6 compounds
Alcohols
The preservative, and the solvent that carries aroma to the nose.
Ethanol, Glycerol, Higher alcohols, 2-Phenylethanol, Isoamyl alcohol and 1 more
11 compounds
Esters
Most of what a cider smells of, and the first thing time takes away.
Ethyl acetate, Isoamyl acetate, Decadienoate esters, Ethyl butanoate, Ethyl hexanoate and 6 more
6 compounds
Aldehydes
Cut apple at one end, bruised and papery at the other.
Acetaldehyde, Acrolein, Hexanal, Vanillin, Furfural and 1 more
2 compounds
Ketones
A short list, but it holds the butter note of diacetyl.
3 compounds
Sulphur compounds
Detectable in traces, and both a fault and a preservative.
2 compounds
Gases
One of them is a texture; the other is a clock.
6 compounds
Additives and processing aids
What is put in deliberately, and what each is for.
Sulphur dioxide, Patulin, Potassium sorbate, Sorbic acid, Ascorbic acid and 1 more
Microbiology — what made it
A spontaneous cider ferment is a succession rather than an organism: what arrives from the press is a mixed population, and what finishes the job is rarely what started it. These records say what each organism does and the conditions that decide whether it gets the chance.
19 recorded
Yeasts
They make the alcohol and most of the aroma, and hand over to each other as the ferment goes on.
Dekkera bruxellensis, Hanseniaspora valbyensis, Saccharomyces cerevisiae, Brettanomyces anomalus and 15 more
13 recorded
Bacteria
The group holding both the softening of a cider and its conversion into vinegar.
Acetobacter aceti, Oenococcus oeni, Acetobacter pasteurianus, Lactiplantibacillus plantarum and 9 more
7 recorded
Moulds
Mostly finished before the mill, and judged by what they left in the fruit.
Penicillium expansum, Botrytis cinerea, Monilinia fructigena, Neonectria ditissima and 3 more
| Role | Recorded | For example |
|---|---|---|
| Primary fermentation | 13 | Saccharomyces cerevisiae, Hanseniaspora valbyensis, Saccharomyces uvarum |
| Secondary fermentation | 6 | Saccharomyces cerevisiae, Dekkera bruxellensis, Zygosaccharomyces bailii |
| Malolactic conversion | 6 | Oenococcus oeni, Lactiplantibacillus plantarum, Lactobacillus collinoides |
| Spoilage | 26 | Dekkera bruxellensis, Acetobacter aceti, Zygosaccharomyces bailii |
| Surface film | 6 | Film yeasts, Acetobacter pasteurianus, Pichia membranifaciens |
| Present throughout | 8 | Saccharomyces cerevisiae, Acetobacter aceti, Acetobacter pasteurianus |
| Orchard pathogen | 0 | None recorded |
Sensory — why it is perceived that way
The bridge between the two sections above and the glass in front of you. Thirteen structural dimensions describe what a cider is made of; twenty aroma families describe what it smells of, and every descriptor filed under them names its cause.
13 dimensions
Structure
Sweetness, acidity, tannin, body and the rest, each scored one to five as a band rather than a point, with the mechanism behind the sensation and the dimensions it is routinely mistaken for.
Sweetness, Acidity, Bitterness, Tannin, Astringency, Body, Carbonation, Alcohol, Freshness, Fruit character, Phenolic character, Fermentation character, Oxidative character
20 families · 138 descriptors
Aroma and flavour
From fresh apple to the volatile faults, each family stating where its aromas come from and whether meeting one usually indicates a problem. A descriptor that cannot say what produces it is not published.
Fresh apple, Ripe apple, Cooked and baked apple, Pear, Citrus, Stone fruit, Tropical fruit, Berry and 12 more
Explainers
Longer pieces that cut across the records: a question, a direct answer, and then the depth.
The acids in cider
Malic acid supplies nearly all the acidity of apple juice; lactic acid replaces part of it if malolactic fermentation runs; acetic acid indicates spoilage; citric acid matters in pears and not in apples. Each tastes different.
The chemistry of apple juice
What is dissolved in pressed apple juice, in what proportions, and which components matter to fermentation. Mostly water and sugar, with acid, phenolics, pectin, nitrogen and minerals in the fractions that decide everything else.
What cider science does not yet know
The genuine open questions: whether measured phenolics predict perceived astringency in finished cider, what non-Saccharomyces yeasts actually contribute, whether regional wild-yeast populations leave a reproducible signature, and how little modern analysis exists for most cultivars.
What fermentation actually does
Yeast converts sugar to ethanol and carbon dioxide by glycolysis, and in doing so runs a whole metabolism whose by-products — glycerol, esters, higher alcohols, acids and sulphur compounds — become most of what a cider tastes of.
Where cider flavour comes from
Four sources: the fruit, the fermentation, the microbial activity that follows it, and time with air. Most of what a cider smells of was made by yeast rather than carried in from the apple.
Why tannin is both bitter and astringent
Bitterness is a taste and astringency is a tactile sensation, and the same phenolic material produces both. The split is governed chiefly by chain length: short procyanidin oligomers taste bitter, long polymers precipitate salivary protein and dry the mouth.
Oxidation, from the mill to the bottle
Two different processes share the name. Enzymatic browning happens in minutes in fresh juice and is driven by polyphenol oxidase; chemical oxidation happens over months in finished cider and generates acetaldehyde and sherry character.
Perry chemistry, and what is actually different
Four things genuinely separate pear juice from apple juice — sorbitol, citric acid, nitrogen and the way pear tannin is perceived. Two more are repeated constantly and do not survive the evidence.
pH versus titratable acidity
Titratable acidity measures how much acid is present; pH measures how strongly it is dissociated. Sourness tracks the first, microbial risk tracks the second, and buffering capacity means neither predicts the other.
Reading a juice analysis
What each figure on a juice analysis actually governs, in what order to read them, and which pairs of numbers are the ones that decide how a ferment will go.
Sorbitol and why perry behaves differently
Pears carry substantial sorbitol, a sugar alcohol that yeast does not ferment. It survives into the finished perry, tastes sweet, adds body, and makes a fully fermented perry something a fully fermented cider cannot be.
Sugar and the perception of sweetness
How sweet a cider tastes is not a readout of its sugar content. Acid suppresses sweetness, tannin opposes it, carbonation sharpens the palate, alcohol and glycerol add sweetness of their own, and aroma can create the impression without any sugar at all.
Sulphur dioxide, and why pH governs it
Only the molecular form of sulphur dioxide is antimicrobial, and what fraction of the free sulphite is molecular depends steeply on pH. The same addition is several times more effective at pH 3.2 than at pH 3.8.
The aroma families and where each comes from
Twenty families cover what cider and perry smell of, and each is tied to the compound or process that produces it. A descriptor that cannot say why it arises is an adjective; one that can name a molecule is information.
The difference between a fault and a style feature
Most cider faults are compounds that are welcome somewhere. What makes something a fault is concentration relative to a threshold, and the expectations of the style it appears in. A handful of characters are faults everywhere.
The nitrogen problem in cider juice
Cider apple juice is often much poorer in assimilable nitrogen than wine must, which makes fermentations slow, prone to stalling, and liable to produce sulphide off-flavours. Traditional practice turns the same deficiency into a technique.
The sensory model CiderHQ uses
Thirteen dimensions, each scored as a band rather than a point, divided into structural, textural and aromatic families. The band is the honest shape, because a style covers a real range and a single number would assert a precision the evidence does not support.
What the press does to the juice
Milling decides how much juice can be released, maceration decides how much phenolic comes with it, and the press decides how much air the juice meets on the way out. The three are one decision, not three.
Why cider fermentations stall
A fermentation stops when the yeast cannot continue, and the usual reasons are nitrogen deficiency, cold, excessive sulphite, an unhealthy population from the start, or the combined stress of alcohol and low pH.
How a trained sensory panel works
A panel is an instrument. Assessors are screened, trained on a shared lexicon and calibrated with reference standards, then used to measure intensity or to detect difference under controlled conditions with replication.
How carbonation changes taste
Dissolved carbon dioxide is chemically and physically active. It forms carbonic acid on the tongue, stimulates the trigeminal nerve directly, suppresses perceived sweetness, and carries aroma out of the glass faster.
How temperature changes taste
Cold suppresses aroma release and blunts sweetness; warmth releases volatiles and increases the perception of alcohol and sweetness. Bitterness and astringency are relatively less suppressed by cold, so a chilled tannic cider reads as harsher.
What ageing does to cider
Tannins polymerise and eventually precipitate, esters slowly hydrolyse, oxidation products accumulate, and in bottle-conditioned cider the yeast autolyses. Bitterness declines, fruit aroma fades, and oxidative and honeyed characters rise.
The datasets behind the numbers
Every measured figure on this site came from one of eleven measurement programmes. These pages say what each one measured, where, when and by what method — and, crucially, which of them may be read in one column with which.
Kingston Black comes out at pH 3.51 in the Skagit Valley and 4.23 in the Finger Lakes, and neither figure is wrong. A measurement is a statement about a fruit and a place and a season and a method, and a site that averaged the two would be publishing a number nobody measured.
The DOP Sidra de Asturias varietal characterisation
The Consejo Regulador’s published characterisation of the apple varieties the Asturian designation admits, sorted into nine technological blocks rather than four English classes, and reported in a unit nothing else on the site uses.
The Long Ashton cider apple table
The acid and tannin figures behind almost every English cider apple classification, compiled from analyses made between 1905 and 1975 — and reaching CiderHQ third-hand, which is stated on every number.
The Three Counties perry pear survey
A modern survey of single-variety perry pear juices from Gloucestershire, Herefordshire and Worcestershire — the first dataset to separate the astringent phenolics from the ones that only brown, and the first to measure the nitrogen.
The USDA-PGRU germplasm characterisation
The largest single-season cider characterisation on the site: forty-seven accessions from the United States national apple collection, twelve properties each, all picked in one autumn.
The WSU Mount Vernon cider cultivar trial
Fifteen seasons of European cider fruit grown in the Skagit Valley, and the clearest evidence CiderHQ holds that a cider apple’s class is a statement about a place as much as about a fruit.
The Geneva finished-cider analyses
The only dataset on the site measured on finished cider rather than on juice, which makes it the clearest demonstration of why that distinction is not pedantry.
What this section will not do
CiderHQ gives no addition rates. What an additive does and what regulators limit are recorded; the figure to use depends on the juice in front of you and on the law where you are, and it belongs to your supplier and your regulator rather than to a general reference.
Species-level microbiology is reasonably well described in the literature. Strain-level behaviour within a species varies enormously and is not asserted here.
House populations in a working cidery are real and well evidenced. A wild yeast signature distinguishable from the next valley’s is a much stronger claim, and these records decline to make it.
- The evidence policy — what each confidence tier means and how sources are recorded.
- Making cider — the processes this chemistry is the explanation for.
- Troubleshooting — the same science, entered from a problem rather than from a molecule.