Science

The compounds in cider

A cider is a few hundred grams of dissolved apple and a few grams of things the yeast made. Almost every question about why one tastes different from another has an answer at this level.

CiderHQ holds 80 compound records. Each one says what the compound does, how it is perceived and at roughly what concentration, what forms it, what removes it and which faults it is implicated in. A record that could only list a molecular formula would not be worth writing.

Numbers appear only where they can carry their context — a property, a unit, a source and the conditions the figure was taken under. A good many real and useful concentrations in cider chemistry have no home in that structure, and those are stated in prose with the institute or instrument named rather than dressed up as analysis.

The ones you can smell or taste

Compounds with a recorded sensory effect, and the words most often used for them. These are the entries to start from if you are trying to put a name to something in the glass.

What each compound is perceived as. The words are the ones in general use, not a controlled vocabulary — the descriptor pages under Sensory are where a word is tied back to its cause.
Compound	Class	Perceived as
Acetaldehyde	Aldehydes	bruised apple, sherry, green nut, cut grass at low level, flat and papery in combination with oxidation
Acetic acid	Acids	vinegar, sharp, nail varnish when accompanied by its ester, sour finish, nose prickle
Carbon dioxide	Gases	prickle, fizz, sharpening, foam, lifted aroma
Ethanol	Alcohols	warming, faintly sweet, full, spirituous at high strength
Malic acid	Acids	sharp, green apple, mouth-watering, crisp, lingering sourness
Pectin	Polysaccharides	fullness, slight viscosity
Polyphenol oxidase	Enzymes	browning, loss of fresh aroma, softened tannin, nutty depth in deliberately oxidised juice
Procyanidins	Phenolics	drying, grippy, bitter, chewy, walnut skin, tea-like
Sorbitol	Sugar alcohols	soft sweetness, roundness, cooling
Sulphur dioxide	Additives and processing aids	struck match, burnt rubber at high free levels, suppressed aroma, bleached colour
4-Ethylphenol	Phenolics	horse, stable, sticking plaster, leather, smoke, medicinal, barnyard
Dissolved oxygen	Gases	bruised apple, sherry, cardboard, flat, nutty depth in controlled exposure
Ethyl acetate	Esters	pear drop, nail varnish, solvent, glue, lifted fruit
Fructose	Sugars	sweet, clean, fruit-sugar sweetness
Lactic acid	Acids	soft acidity, yoghurt, milky, rounded sourness
Total phenolics	Phenolics	structure, grip, bitterness
Chlorogenic acid	Phenolics	mild bitterness, faint astringency
Citric acid	Acids	bright, citrus, immediate sourness
Diacetyl	Ketones	butter, butterscotch, popcorn, cream, rancid at high level
Epicatechin	Phenolics	bitter, faintly astringent, green
Glucose	Sugars	clean sweetness
Glycerol	Alcohols	weight, slight viscosity, faint sweetness
Higher alcohols	Alcohols	solvent, marzipan, nail varnish, warming, rose, whisky-like
Hydrogen sulphide	Sulphur compounds	rotten egg, drains, struck flint at trace level, sewage
Hydroxycinnamic acids	Phenolics	mild bitterness, slight astringency
Isoamyl acetate	Esters	banana, pear drop, boiled sweets, juicy fruit
Potassium sorbate	Additives and processing aids	neutral at working concentrations, crushed geranium leaf where bacterial conversion has occurred
Sorbic acid	Additives and processing aids	neutral at working concentrations, faint plastic or waxy note at high addition
Sucrose	Sugars	plain sweetness
Tannin–protein complexes	Phenolics	drying, rough, chalky, grippy, cumulative across sips
2-Phenylethanol	Alcohols	rose, honey, blossom, lilac
4-Ethylguaiacol	Phenolics	smoke, clove, bacon, spice, medicinal
4-Vinylguaiacol	Phenolics	clove, spice, smoky, medicinal
Acrolein	Aldehydes	intense bitterness, acrid, peppery, lingering
Beta-glucan	Polysaccharides	oily texture, slimy, thick, thread-forming
Biogenic amines	Nitrogen compounds	coarse, metallic, faintly putrid at high concentration
Catechin	Phenolics	mild bitterness, slightly drying
Decadienoate esters	Esters	pear, pear flesh, ripe orchard pear
Ethyl butanoate	Esters	pineapple, ripe apple, sweet fruit, bubblegum
Ethyl hexanoate	Esters	green apple, aniseed, fruit gum, brandy
Ethyl lactate	Esters	milky, creamy, soft, buttery-adjacent
Ethyl octanoate	Esters	ripe pear, apricot, waxy, soap at high concentration
Gallic acid	Phenolics	sour astringency, dry, inky
Hexanal	Aldehydes	cut grass, green apple, leafy, green
Hexyl acetate	Esters	apple skin, pear, fresh fruit, sweet green
Isoamyl alcohol	Alcohols	marzipan, solvent, malt, warming
Mercaptans	Sulphur compounds	onion, garlic, cooked cabbage, burnt rubber, drains
Oak lactones	Esters	coconut, wood, cedar, creamy, sawn timber
Phloridzin	Phenolics	bitter, apple pip
Quinic acid	Acids	drying, faintly astringent, sour
Succinic acid	Acids	salty, bitter-sour, savoury
Terpenes	Phenolics	elderflower, rose, citrus peel, pine, lavender, hop
Tetrahydropyridines	Nitrogen compounds	mouse cage, stale popcorn, cracker, corn chips, delayed and lingering aftertaste
Vanillin	Aldehydes	vanilla, custard, sweet wood, cream
Acetoin	Ketones	cream, yoghurt, faint butter
Anthocyanins	Phenolics	colour only
Benzoic acid	Additives and processing aids	neutral at low addition, faintly acrid or medicinal at high addition
Dimethyl sulphide	Sulphur compounds	cooked sweetcorn, cabbage, asparagus, tinned vegetable, savoury depth at trace
Ethyl decanoate	Esters	waxy, oily, faint floral, soapy
Eugenol	Phenolics	clove, allspice, warm spice, medicinal at high level
Furfural	Aldehydes	almond, toast, caramel, cooked, burnt sugar
Lactones	Esters	peach, apricot, coconut, creamy stone fruit
Quercetin glycosides	Phenolics	fine astringency, faint bitterness
trans-2-Hexenal	Aldehydes	leaf, green stem, sharp green, unripe

By what kind of molecule it is

Ordered by where the compound enters the drink: what the fruit arrives carrying, then what the ferment makes of it, then what a maker puts in deliberately.

Sugars (3)

What the yeast is given to work with, and what is left when it stops. Fructose predominates in apple juice, which matters because it is the sugar yeast leaves until last.

Sugar alcohols (1)

Sweet to taste and largely unfermentable, which is why a perry can read as sweet on the palate and dry on the hydrometer.

Sorbitol

Acids (8)

The sharpness, and the thing that keeps the drink microbiologically safe. Malic acid comes from the fruit; lactic and acetic acid are made after it.

Phenolics (17)

Tannin, bitterness, astringency and colour. The chain length of a procyanidin decides whether the mouth registers a taste or a texture.

Polysaccharides (5)

Pectins and their relatives: what makes juice cloudy, what makes it hard to press, and what keeving works on.

Nitrogen compounds (7)

Yeast food. Apple juice is nitrogen-poor compared with grape must, and most stuck ferments and most sulphur smells trace back to that fact.

Enzymes (3)

Catalysts carried in the fruit or added deliberately, which change the juice without being consumed by it.

Alcohols (6)

Ethanol and the higher alcohols alongside it — the preservative, the solvent that carries aroma, and a set of by-products the ferment cannot avoid making.

Esters (11)

Most of what a cider smells of. Formed by yeast from alcohols and acids, and lost steadily to time and hydrolysis.

Aldehydes (6)

Cut apple at one end and bruised, papery oxidation at the other. Several are made by the act of milling the fruit rather than by the ferment.

Ketones (2)

A small family, but it contains diacetyl — the butter note that malolactic fermentation brings with it.

Sulphur compounds (3)

Perceptible at vanishingly small concentrations, and responsible both for the drink’s commonest reductive fault and for its commonest preservative.

Gases (2)

Carbon dioxide and oxygen: one of them is a texture and the other is a clock.

Additives and processing aids (6)

Things put in on purpose. CiderHQ records what each does and why it is used, and gives no dosages — that is a food-safety decision that belongs to a regulator and a supplier.

Every compound

All compound records on CiderHQ, alphabetically, for the reader who arrived knowing the name.

On dosages and limits

No page in this section gives an addition rate. What a compound does, how it behaves and what regulators limit are all recorded; the figure to actually use depends on the juice in front of you and on the law where you are, and it comes from your supplier or your regulator rather than from a general reference.

Microbiology — the organisms that make most of these compounds, and the conditions that decide which ones.
Sensory — the perception each compound produces, and the words for it.
Troubleshooting — what happens when one of these is present in the wrong quantity.