Cider science

The chemistry of apple juice

What is apple juice actually made of?

In short

By mass, apple juice is around 85–90% water. Most of the rest is sugar — fructose predominantly, with glucose and sucrose — and it is that sugar which sets how much alcohol the juice can produce.

The minority components decide almost everything else. Malic acid supplies nearly all the acidity; phenolic compounds supply bitterness, astringency and colour; pectin governs clarity and makes keeving possible; and nitrogen, present in small and highly variable quantities, governs how the fermentation runs.

None of these is constant. Every one varies with variety, season, orchard, ripeness and how the fruit was handled, which is why a single figure for any of them is only ever a figure for a particular pressing.

Sugar, acid, phenolics and nitrogen as they arrive in the juice and as they leave the ferment.

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.

What is in it, by fraction

The principal components of pressed apple juice and what each governs. Proportions are indicative and vary widely by variety and season.
Component	Roughly how much	What it governs
Water	About 85–90% by mass	The solvent; everything else is dissolved or suspended in it
Sugars — fructose, glucose, sucrose	The great majority of the dissolved solids: roughly 100–130 g/L in a juice reading the usual 11.5–14 °Brix	Potential alcohol, and sweetness in juice and in any cider fermented short of dryness
Malic acid	The dominant acid, with traces of quinic, citric and others. The middle half of the apple juices measured here titrate at about 3.5–7 g/L as malic	Acidity, pH, microbial safety, and the perception of freshness
Phenolics — procyanidins, chlorogenic acid, phloridzin, others	Under about 2 g/L (0.2%) in sweets and sharps; above it, by the Long Ashton definition, in bittersweets and bittersharps	Bitterness, astringency, colour, browning and ageing capacity
Pectin	A small but significant fraction	Viscosity, clarity, press yield, and whether keeving is possible
Nitrogen compounds — amino acids and ammonium	Small and highly variable: 108 Virginia juices ranged from 9 to 249 mg N/L of assimilable nitrogen, mean 59	Fermentation speed and completion, and whether the yeast produces sulphide off-flavours
Sorbitol	Small in apples; large in pears	Unfermentable sweetness and body
Minerals, chiefly potassium	Trace	Buffering capacity, and therefore how much acid a given pH corresponds to
Starch	Present in under-ripe fruit, absent when fully ripe	Haze in the finished cider where fruit was pressed too early

What the juices measured on this site actually read

Ranges in a textbook are someone’s summary. The table below is not: it is every apple-juice measurement held on this site, drawn from the cultivar records at the moment the page was built, with the quartiles of each distribution and a count of how much evidence stands behind it. The programmes behind it pressed fruit in England, France, Spain and the United States across more than a century, so the spread is real variation between cultivars, sites and seasons rather than noise around one true juice.

Three things stand out. Gravity is the tightest property: the middle half of the juices fall within about ten points of each other, which is why most unadjusted ciders end within a couple of percentage points of strength of one another. Acidity is the widest, with the upper quartile roughly double the lower, which is the axis the cider apple classes are built on. And pH spreads further than acidity alone would predict, because the potassium that sets a juice’s buffering varies independently of its acid — two juices of the same titratable acidity can sit several tenths of a pH unit apart.

Titratable acidity is shown as malic acid throughout. Spanish figures are published as sulphuric acid and are restated here; leaving them as published would put two conventions a third apart into one distribution.

What the apple juices measured on this site actually read: every apple cultivar measurement in the corpus, by property, with the quartiles of the distribution. Each figure is one pressing in one place and season; the table describes the evidence, not an ideal juice.
Property	Lowest	Lower quartile	Median	Upper quartile	Highest	Readings (distinct)	Programmes
Specific gravity (SG)	1.040	1.047	1.051	1.057	1.079	77 (29)	4
Brix (°Bx)	8.1	11.7	12.8	13.6	18.7	117 (54)	4
pH (pH)	2.95	3.48	3.67	4.12	4.70	129 (81)	5
Titratable acidity (g/L)	0.9	3.7	5.3	7.0	12.1	120 (82)	3
Total acid (% w/v)	0.11	0.21	0.33	0.67	1.91	169 (75)	6

Measured by: Washington State University cider research programme; Typical Apple Juice Analysis (NACM Short Report 4.11); Caractérisation de jus de pomme à cidre et analyse comparative avec des jus de pomme commerciaux; Cornell Cider Research and Extension programme; Characterization of Malus Genotypes within the USDA-PGRU Malus Germplasm Collection for their Potential Use within the Hard Cider Industry; Characterization of the Polyphenol Composition of 20 Cultivars of Cider, Processing, and Dessert Apples (Malus × domestica Borkh.) Grown in Virginia; Denominación de Origen Protegida Sidra de Asturias; Cider Apple Compositional Data; Long Ashton Research Station cider fruit analyses; A Somerset Pomona: The Cider Apples of Somerset. The same distributions are what the juice analysis interpreter places your own readings against.

Juice analysis interpreter — place your own gravity, pH and acidity readings against these same distributions.
Titratable acidity — turn a titration into grams per litre in all three acid conventions.
How strong cider is — what the gravity distribution means for the strength a cider can reach.

What this table cannot tell youThe corpus over-represents what research stations chose to measure: heritage cider fruit in England, the Asturian varieties the designation lists, and germplasm collections in the United States. Commercial dessert-apple juice is in it, but not in proportion to how much of it is pressed. A reading outside these ranges is unusual for this evidence, not necessarily unusual for apples.

Sugar, and why the composition matters as well as the amount

Fructose is the largest single sugar in apple juice, with glucose and sucrose making up the rest; sucrose is hydrolysed to glucose and fructose early in fermentation. All three are fermented by Saccharomyces cerevisiae, though not at the same rate: glucose is consumed preferentially and fructose more slowly, which is why the last stages of a ferment are disproportionately fructose and why a stuck ferment leaves fructose behind.

That matters sensorially because fructose is the sweetest of the common sugars on a per-gram basis. A cider that has stopped short therefore tastes sweeter than its total sugar figure alone would suggest, because what is left is enriched in the sweetest component.

Total dissolved solids are measured as specific gravity or in degrees Brix, and both are used to estimate potential alcohol. The estimate is approximate rather than exact, because a hydrometer responds to everything dissolved rather than to sugar alone, and non-fermentable material — sorbitol, acids, phenolics — contributes to the reading.

The three sugars in forty-seven apples, in proportion

One programme assayed glucose, fructose and sucrose separately, by one enzymatic method, in forty-seven of the cultivars on this site: the United States apple collection at Geneva, New York, in 2017. In the published mean for every one of the forty-seven, fructose outweighed glucose. The median juice carried a little over three grams of fructose for every gram of glucose, and the middle half of the collection lay between about two and a half and four to one. The ends of the range are not quoted: they rest on single assays whose replicates disagree widely.

That ratio is what decides the sugar left in a ferment that stops early. Yeast takes glucose first, so the longer a ferment runs the more of what remains is fructose, and in a juice that already starts at three to one the residue of a stalled or arrested ferment is overwhelmingly the sweetest of the three. Two ciders stopped at the same gravity can therefore taste differently sweet, and the one made from a high-ratio juice is the sweeter.

Sucrose made up a median of three tenths of the fermentable sugar, and between a quarter and a little over a third in the middle half of the collection. Yeast splits it early and ferments both halves, so the share changes nothing about how far a juice can ferment. It changes what a quick test reports: sucrose is not a reducing sugar, so a reducing-sugar strip or tablet used on unfermented juice misses it, and in this collection that was a median of three tenths of the total.

The sugars Characterization of Malus Genotypes within the USDA-PGRU Malus Germplasm Collection for their Potential Use within the Hard Cider Industry assayed in 47 apple juices, one enzymatic method, one season. Proportions are computed per variety from the published means and then summarised; the ends of each range rest on single uncertain assays and are not shown. Drawn live from the cultivar records.
Measure	Lower quartile	Median	Upper quartile
Fructose to glucose, by mass	2.6:1	3.2:1	3.9:1
Fructose, share of the three fermentable sugars	48%	52%	55%
Sucrose, share of the three fermentable sugars	25%	30%	37%

The USDA-PGRU germplasm characterisation — every property the collection measured, and the cultivars behind each figure.
Sugar and the perception of sweetness — why the same sugar reads differently sweet against acid, tannin and aroma.
Sorbitol and why perry behaves differently — the sugar alcohol the yeast leaves behind, and how large a share of the sugar it is in apples.

Why only proportions are givenThe same programme also read every juice on a refractometer, and for several varieties the summed sugars do not fit the reading: Bramley’s Seedling is recorded at 139 g/L of the three sugars against 8.9 °Brix, which allows about 92 g/L of dissolved solids of every kind, and Brown’s Apple at 24 g/L against 8.3 °Brix. Whether the two analyses were run on different samples, or a figure was transcribed wrongly, has still to be checked against the original tables. A ratio between two sugars from the same assay does not depend on that answer, so ratios are what this page uses.

The phenolic fraction is where cider fruit is different

Apple phenolics fall into several classes. The procyanidins are polymers of catechin and epicatechin units and are the material usually meant by cider tannin; the hydroxycinnamic acids, chiefly chlorogenic acid and p-coumaroylquinic acid, are the principal substrates for enzymatic browning; phloridzin is a dihydrochalcone essentially specific to apple; quercetin glycosides sit in the skin; and anthocyanins appear in red-fleshed varieties.

The distribution across these classes differs by variety far more than the total does, and it is the distribution rather than the total that predicts the palate. In particular, the mean degree of polymerisation of the procyanidins — the average chain length — governs the split between bitterness and astringency, and two juices with identical total phenolics can behave quite differently if their chain-length distributions differ.

Phenolics are concentrated in the skin and in the tissue immediately beneath it, which is why milling fineness and maceration time have such a large effect on how much ends up in the juice. A gentle whole-fruit press extracts markedly less than a finely milled pomace left to stand.

The components that are easy to overlook

Nitrogen is the one that most often decides whether a fermentation works. Yeast requires assimilable nitrogen — free amino acids and ammonium — to build the machinery for consuming sugar, and cider apple juice frequently carries far less than a wine must. Traditional cider varieties from low-input orchards are often at the low end, which is a large part of why traditional ciders ferment slowly and why keeving works at all.

Pectin governs whether the juice will clarify and whether it can be keeved. It is a chain of galacturonic acid units with methyl groups attached; the enzyme pectin methylesterase removes those groups, which allows calcium to cross-link the chains into a gel. Commercially, pectinase preparations are added to do the opposite — break the pectin down so the juice clears and presses more freely.

Potassium, present as a mineral, sets much of the juice’s buffering capacity. Two juices with the same titratable acidity can sit at noticeably different pH values if their potassium content differs, which is one reason pH and titratable acidity have to be measured separately rather than inferred from one another.

Why this page gives ranges rather than numbersPublished analyses of apple juice come from particular cultivars, grown at particular sites, in particular seasons, by particular methods. Averaging them would produce an authoritative-looking figure that describes no real juice. Where a number is quoted on this site it carries the context that makes it meaningful.

Also answered on this page

Questions this page covers, so you can tell at a glance whether it is the one you want.

How much sugar is in apple juice?
What acid is in apples?
What are apple polyphenols?
Why is nitrogen important in cider juice?
What is Brix?

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.

What acids are in cider and what does each taste like — Malic acid is the dominant acid in apple juice and in most cider, and it tastes sharp, clean and persistent — the acidity of a green apple. Lactic acid, produced when bacteria convert malic acid, is softer and rounder and reads as creamy rather than sharp.
What is malic acid and why does it matter in cider — Malic acid is the acid of apples and supplies almost all the sharpness a cider has. It also sets pH, which decides how well sulphite works and how exposed the cider is to spoilage, so it does far more work than its taste suggests.
What is the difference between bitterness and astringency in cider — Bitterness is a taste, detected by receptors on the tongue. Astringency is not a taste at all: it is a mechanical sensation caused by tannins binding and precipitating the proline-rich proteins in saliva, which strips away the lubricating film in the mouth.
How do i know when cider fermentation has finished — Stable gravity readings several days apart, not the airlock going quiet. A ferment that has stalled and a ferment that has finished both stop bubbling, and only a hydrometer tells you which one you have.
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.
What does pectin do in cider — Pectin is the structural polysaccharide that holds fruit cells together. In juice it holds haze in suspension, and it is the molecule keeving depends on: strip its methyl groups and it will gel with calcium and float the nutrients out of the juice.

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.
Long Ashton Research Station cider fruit analyses
National Fruit and Cider Institute / University of Bristol · research institute · registered as competent for this subject · covers 1903–2003
The foundational body of cider-fruit science in English. Long Ashton produced the acid-and-tannin classification that divides cider apples into sweet, sharp, bittersweet and bittersharp, and analysed hundreds of cultivars grown at its Somerset site. Its figures are historic measurements of specific fruit at a specific place, not universal constants — a distinction CiderHQ preserves in every measurement record that cites it.
Institut national de recherche pour l’agriculture, l’alimentation et l’environnement (INRAE)
INRAE · research institute · retrieved 2026-08-24
French national agricultural research. Its Angers programme produced much of the published work on apple procyanidin chain length and on the relationship between polymer size, bitterness and astringency.
Cornell Cider Research and Extension programme
Cornell University, School of Integrative Plant Science · university · passage verified 2026-08-24
Runs cultivar trials in New York State and publishes juice chemistry for European cider varieties grown in a North American climate — the single most useful counterweight to treating English figures as universal.
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.
Free amino nitrogen concentration correlates to total yeast assimilable nitrogen concentration in apple juice
Boudreau, Peck, O’Keefe and Stewart, Food Science & Nutrition 6(1):119–123 · peer-reviewed literature · passage verified 2026-08-24 · covers 2014–2015
Open access; read in full on 2026-08-24. The paper that gives cider its own nitrogen numbers instead of borrowing wine’s. A hundred and eight apple samples from Virginia over two seasons, with the two fractions of assimilable nitrogen measured separately — which matters, because the finding is that apple juice is short of ammonium specifically, and that the wine practice of measuring both fractions may be unnecessary for apples while the wine practice of assuming there is enough nitrogen is badly wrong.
Washington State University cider research programme
Washington State University Northwestern Washington Research and Extension Center · university · passage verified 2026-08-24
The single most useful open cider dataset CiderHQ has found. The programme’s cultivar performance database gives juice chemistry, orchard behaviour, bloom and harvest timing and cider-maker tasting notes for 73 cultivars grown at one maritime site over fifteen years, and — unusually — publishes its classification thresholds alongside its figures, so the classification can be checked rather than taken on trust. It also states outright that its results diverge from the English ones. Read in full on 2026-08-24 and transcribed into `data/trials/wsu-mount-vernon.ts`; four published figures were found to be impossible and are withheld there with their reasons.
Characterization of Malus Genotypes within the USDA-PGRU Malus Germplasm Collection for their Potential Use within the Hard Cider Industry
Cornell University / USDA-ARS Plant Genetic Resources Unit · university · passage verified 2026-08-25 · covers 2017 harvest
A Cornell masters thesis, open access, read in full on 2026-08-25 including the supplemental tables. The largest single-season cider characterisation CiderHQ holds: 158 accessions from the United States national apple collection, each measured for fruit weight and diameter, starch pattern index, firmness, soluble solids, titratable acidity, pH, total phenolics and the four sugars separately. Every mean is published with its standard deviation, which is why CiderHQ can store dispersion here and cannot for most historic tables. Forty-seven of the accessions correspond to cultivars the site already holds; the figures are transcribed for those and the accession identifier is recorded against each, because a germplasm label is a claim about identity rather than a proof of one.
Denominación de Origen Protegida Sidra de Asturias
Consejo Regulador de la DOP Sidra de Asturias · designation authority · passage verified 2026-08-24
The regulating council for Asturian cider. Read on 2026-08-24, and it turned out to carry far more than a permitted-variety list: an agronomic and technological characterisation of each admitted variety, with total acidity, total polyphenols, vigour, flowering, ripening, cropping and susceptibility to fungal disease. The characterisation is credited to SERIDA’s fruit-research programme. Two things it settles are corrections to what CiderHQ previously held: Asturias sorts cider fruit into nine technological blocks rather than five, and it publishes acidity as sulphuric acid rather than malic. The figures are transcribed into `data/trials/serida-asturias.ts` and cite this source, because this is where they were read.