Sensory descriptor
Peppery bitterness
A harsh, burning bitterness from acrolein formed when lactic bacteria degrade glycerol.
Also called Amertume, Acrolein bitterness, Bitter cider disease.
- Aroma family
- Volatile and fault-related
- Does it indicate a fault?
- Usually, yes
What causes it
Lactobacillus collinoides and related bacteria can dehydrate glycerol to 3-hydroxypropionaldehyde and thence to acrolein. Acrolein itself is sharply irritant rather than bitter, but it reacts readily with the cider’s phenolic compounds — procyanidins in particular — to form adducts with an intensely bitter, burning quality. The fault is therefore specific to tannic cider: the same bacterial activity in a low-phenolic drink produces far less of it. It was described in French cider literature as amertume long before its chemistry was understood, and it remains a recognised problem in traditional bittersweet production.
No level is acceptable, and it is distinguished from ordinary tannin bitterness by its burning, persistent quality and by the fact that it appears during storage in a cider that did not have it before.
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.
Acrolein
A sharp aldehyde made by lactic bacteria from glycerol, which reacts with tannin to produce an intense, lingering bitterness in cider that was sound when it was bottled.
Glycerol
A syrupy three-carbon alcohol yeast produces as a side reaction of fermentation, which adds weight to a dry cider and is the raw material for one of its more obscure faults.
Procyanidins
The condensed tannins of cider fruit, whose chain length — not their quantity — decides whether the mouth registers bitterness or astringency.
Lactic acid
The softer acid that replaces malic when malolactic fermentation runs, halving the acid a cider carries and changing its texture as much as its sharpness.
The organisms that make it
Where a specific organism is implicated rather than the fruit. Naming one answers a different question from naming a molecule: what is in the cellar, rather than what is in the glass.
What raises it
Processes that increase this character, or preserve it where it would otherwise be lost.
Sulphite stabilisation
Managing free sulphur dioxide through maturation and at packaging so that a useful antimicrobial and antioxidant fraction survives into the bottle.
Racking
Moving cider off the sediment it has thrown, which both cleans the liquid and — by taking yeast and nitrogen away with the deposit — slows what is left of the ferment.
Acid adjustment
Correcting the acidity of low-acid juice before fermentation, usually with malic acid, and the difference between the pH question and the titratable acidity question.
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
Filtration
Passing cider through a porous medium to reach a stated visual brightness, at a real cost in colloidal material, body and aroma.
The fault it points at
Meeting this descriptor above a certain intensity is how the fault below is usually noticed first.
Fault
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.
About Peppery bitterness
This fault is a good illustration of why cider needs its own fault vocabulary rather than a borrowed one: it requires both glycerol-degrading bacteria and a high procyanidin content, and the combination is far more characteristic of traditional cider than of wine.
It is not reversible. Prevention is the same set of controls as for the other lactic faults — adequate sulphite, sound pH, prompt racking off gross lees.
Others in the volatile and fault-related family
Vinegar, glue, mousiness, sourness out of place.
Vinegar
Acetic acid from acetic acid bacteria oxidising ethanol in the presence of air — the classic cider spoilage.
Glue
Ethyl acetate at fault concentration, past the solvent stage and into adhesive.
Mousy
A retronasal-only taint of mouse cage and stale grain, from tetrahydropyridines produced by lactic bacteria and Brettanomyces.
Flat and lifeless
The absence of aroma and lift where both were intended — a fault defined by what is missing rather than present.
Metallic
A blood-and-tin taste from dissolved iron or copper, which also catalyses oxidation.
Ropy
An oily, viscous, pouring-in-a-thread texture from bacterial exopolysaccharide, with little aroma of its own.
Acetone
A harsher, more chemical solvent note than ethyl acetate alone, from ketones alongside high volatile esters.
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.
- How do i sterilise cider bottles — Wash them clean first, then sanitise with a no-rinse sanitiser or a sulphite solution, and fill while still wet with it. Bottles that look clean but have dried deposits inside are the usual source of bottle spoilage.
- What is racking in cider making — Racking is siphoning cider off the sediment it has thrown into a clean vessel, leaving the lees behind. It clarifies the cider and, in traditional practice, is also used to slow a ferment by removing yeast with the lees.
- 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.
- Why does cider contain lactic acid — Because malolactic bacteria converted the malic acid into it. Malic acid has two acid groups and lactic acid has one, so roughly half the titratable acidity disappears and the cider tastes softer.
- Do i need a filter to make cider
- How do you adjust the acidity of cider
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.
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.
Institut Français des Productions Cidricoles (IFPC)
IFPC · research institute · retrieved 2026-08-24
The French technical institute for cider production. The authority for the French cultivar classification families, for keeving as an industrial process, and for the pectin and nitrogen chemistry that keeving depends on.
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.