Sensory descriptor
Grapefruit
A bitter-edged citrus note from volatile thiols released by yeast, distinct from acid-driven lemon character.
Also called Grapefruit peel.
- Aroma family
- Citrus
- Does it indicate a fault?
- No — a normal part of cider and perry aroma
What causes it
Apples carry cysteine- and glutathione-bound precursors of volatile thiols, chiefly 3-sulphanylhexan-1-ol and its acetate. These are odourless in the juice; certain Saccharomyces cerevisiae strains possess the β-lyase activity to cleave them during fermentation and release the free thiol, which has a grapefruit and passion-fruit odour at parts-per-trillion thresholds. Yeast strain selection therefore determines whether this note appears at all from identical fruit, which is why it is a marker of modern cultured fermentation rather than of a cultivar. Bitterness from procyanidins reinforces the peel-like impression on the palate.
Volatile thiols are welcome in the small quantities that read as grapefruit and passion fruit. Related sulphur compounds at higher concentration or in different oxidation states read as cat urine, drains or rubber, and the boundary is narrow enough that thiol-expressive yeasts are handled carefully.
The compounds responsible
Where the molecule is established. Some descriptors in this lexicon name a compound the compound register does not yet hold a record for; those are named in the cause above instead.
Mercaptans
What hydrogen sulphide becomes if it is left alone: onion, garlic and rubber notes that are far harder to remove than the gas they came from.
Procyanidins
The condensed tannins of cider fruit, whose chain length — not their quantity — decides whether the mouth registers bitterness or astringency.
Yeast-assimilable nitrogen
The nitrogen a yeast can actually use, which apple juice is chronically short of — the shortage behind both stuck fermentations and rotten-egg aromas, and the shortage keeving deliberately makes worse.
What raises it
Processes that increase this character, or preserve it where it would otherwise be lost.
Yeast selection
Choosing which cultured strain to pitch, on the basis of the temperature, nitrogen, alcohol and aroma behaviour that separates one commercial yeast from another.
Inoculated fermentation
Starting a ferment by pitching a chosen yeast culture so that one known strain, rather than the fruit’s resident population, does the work.
Fermentation temperature control
Managing the temperature at which a ferment runs, which sets not only how fast it goes but which aromatics survive it and what the finished cider tastes of.
Sulphiting
Adding sulphur dioxide to juice to suppress spoilage organisms and oxidative browning, at a level that only means anything once the juice pH is known.
Where it is usually met
Fruit and styles this character is recorded in. A record here is where the descriptor is commonly found, not a claim that every example shows it.
About Grapefruit
Grapefruit is a relatively new descriptor in cider and belongs squarely to modern cultured fermentation, where yeasts developed for Sauvignon Blanc and similar aromatic white wines have been adopted for cider. It is essentially absent from traditional wild-fermented production.
In hopped cider the same word covers a different cause entirely — hop-derived terpenes and thiols from the hop cone — and the two should be distinguished in any note where hops are involved.
Others in the citrus family
Lemon, grapefruit peel, lime zest.
Lemon
A sharp citrus impression built from high malic acid read alongside light esters and terpene traces.
Citrus pith
A dry, bitter citrus note where phenolic bitterness sits alongside sharp acidity rather than behind fruit.
Lime
A green, zesty citrus impression from very high malic acidity combined with the green aldehyde fraction.
Orange peel
A warmer, sweeter citrus note than lemon, usually from terpene traces in matured cider or from added botanicals.
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 temperature should cider ferment at — Most cider is fermented cool, commonly between about 12 and 18 °C. Cooler ferments keep more fruit aroma and run slower; above the low twenties the cider tends towards hot, solvent-like higher alcohols.
- What yeast should i use for cider — CiderHQ does not recommend brands. The choice is between a neutral, reliable strain that lets the fruit show, an aromatic wine strain that adds its own esters, and no addition at all. Alcohol tolerance, cold tolerance and nitrogen demand are the properties worth comparing.
- Can you make cider from shop bought apple juice — Yes, provided the juice contains no preservative — check for potassium sorbate or benzoate on the label. Pasteurised juice ferments perfectly well once yeast is added, because pasteurisation removes the organisms but not the sugar.
- Why is sulphite added to cider — Sulphur dioxide suppresses spoilage bacteria and wild yeast before fermentation and protects the finished cider from oxidation. How much of it is active depends strongly on pH, which is why low-acid juice is harder to protect.
- 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 is yan and why does cider juice run short of it — Yeast assimilable nitrogen is the nitrogen yeast can actually use. Apple juice is usually short of it — in one Virginia survey of 108 samples, 94 per cent fell below the level wine practice treats as a minimum — which is why cider ferments stall more readily than wine ferments.
Where to go next
- The sensory model — The thirteen structural dimensions and the twenty aroma families, in full.
- Compounds — The chemistry behind the words.
- Troubleshooting — When a perception turns out to be a problem, this is where it is diagnosed.
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.
Peer-reviewed literature on cider fermentation microbiology
Various journals · peer-reviewed literature · registered as competent for this subject
Covers the microbial succession of spontaneous cider fermentation, the role of non-Saccharomyces yeasts in the early stages, malolactic conversion by Oenococcus and Lactobacillus species, and the organisms behind the principal spoilage faults.
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.
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.