Sensory descriptor
Butterscotch
Diacetyl at higher concentration with a caramel edge, sitting at the boundary between character and fault.
Also called Buttered popcorn, Toffee-butter.
- Aroma family
- Dairy and lactic
- Does it indicate a fault?
- It depends on the style it is met in
What causes it
Butterscotch is diacetyl above the level at which it reads simply as butter, generally in company with acetoin and with residual sugar or with caramel-type compounds from thermal processing. Acetoin itself has a much higher threshold than diacetyl and is far less aromatic, but at the concentrations produced by extended bacterial activity it contributes a creamy sweetness that shifts the perception from dairy towards confectionery. The route to these levels is prolonged contact with lactic bacteria after the malic acid has been consumed, particularly in warm cellars with oxygen ingress.
This descriptor marks the turn. Where a taster reaches for butterscotch rather than butter, diacetyl has passed the point at which any style framework treats it as characteristic, and the cider is being assessed as faulty in all of them.
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.
Diacetyl
The butter compound, made mainly by lactic acid bacteria and perceptible at very low concentration, which is a defining part of some traditional ciders and an obvious fault in others.
Acetoin
The intermediate between diacetyl and odourless 2,3-butanediol, far less aromatic than the compound it comes from and a useful marker of how far lactic and acetic activity has run.
Fructose
The dominant sugar of apple juice and the sweetest of the common sugars, which is why apple juice tastes sweeter than its total sugar figure implies and why a stuck ferment leaves sweetness behind.
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.
Oenococcus oeni
The acid-tolerant lactic acid bacterium that carries out most deliberate malolactic fermentation, converting malic acid to lactic acid after the yeast has finished.
Pediococcus species
Homofermentative lactic acid bacteria that grow in tetrads, associated in cider with ropiness, diacetyl and slow spoilage during maturation.
What raises it
Processes that increase this character, or preserve it where it would otherwise be lost.
Malolactic fermentation
A bacterial conversion of sharp malic acid into softer lactic acid, which lowers acidity, changes aroma, and in most traditional cider happens whether it was planned or not.
Lees ageing
Deliberately holding a cider or perry on its fine yeast deposit so that autolysing cells release material that changes texture and foam behaviour.
Tank maturation
Resting cider in stainless steel or a lined vessel, where the point of the container is that it contributes nothing and admits almost no oxygen.
Sulphite stabilisation
Managing free sulphur dioxide through maturation and at packaging so that a useful antimicrobial and antioxidant fraction survives into the bottle.
The fault it points at
Meeting this descriptor above a certain intensity is how the fault below is usually noticed first.
Fault
A butter, butterscotch or popcorn character from diacetyl, produced by lactic acid bacteria metabolising citric acid, and by yeast under stress.
About Butterscotch
Butterscotch is useful precisely because it names the threshold. A panel that agrees on butter and a panel that agrees on butterscotch are describing the same compound and reaching opposite verdicts, and that is the honest structure of the judgement.
The remedy once it has formed is limited: yeast contact can reduce diacetyl to acetoin, but a cider already racked, filtered and sulphited has no mechanism left to lower it.
Others in the dairy and lactic family
Butter, butterscotch, yoghurt, cream.
Butter
The buttery note of diacetyl, produced by lactic acid bacteria during malolactic conversion.
Cheesy
A rancid, sweaty note from short-chain fatty acids, chiefly butyric and isovaleric, produced by bacteria.
Cream
A soft, rounded dairy impression from acetoin and lactic acid without the sharpness of free diacetyl.
Soured milk
A sharp, unclean dairy note from uncontrolled lactic activity, recorded as a fault in every style.
Yoghurt
A tangy fermented-dairy note from lactic acid with acetaldehyde, indicating vigorous bacterial activity.
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 is malolactic fermentation — Malolactic fermentation is a bacterial conversion of sharp malic acid into softer lactic acid, releasing carbon dioxide. It lowers total acidity and raises pH, and in cider it is often the source of a farmyard or buttery note as well.
- Which bacterium carries out malolactic fermentation in cider — Oenococcus oeni, in cider as in wine. Genome studies find that the cider strains are genetically distinguishable from the wine ones and that the strain most basal to the whole species was isolated from cider.
- Which sugar is most of the sugar in apple juice — Fructose, by a long way. Apple juice carries roughly twice as much fructose as glucose, with a smaller amount of sucrose, and fructose is the sweetest of the three on the tongue.
- How is cider matured
- How long can cider sit on its lees
- What is acetoin in cider — A buttery-smelling ketone made by both yeast and lactic acid bacteria, and the compound diacetyl is reduced to. It is far less potent than diacetyl, so acetoin forming is usually the butter character fading.
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.
Cider and perry production technical training material
Peter Mitchell / Cider and Perry Academy · reference work · registered as competent for this subject
Searched again on 2026-08-25 and it remains the one printed source here that a bibliographic check cannot fix, because it is not a published work with an edition. It is course material issued to participants of a training programme, so there is no catalogue record to verify, no ISBN, and no lawful public copy. Its state stays `registered` for that reason rather than through inattention.
BJCP Beer Style Guidelines — cider and perry categories
Beer Judge Certification Program · classification framework · retrieved 2026-08-24
Opened on 2026-08-24, and the edition matters. CiderHQ registered the 2015 cider guidelines; BJCP has since published a 2025 cider edition, and the old URL now redirects into the current guidelines index. A competition style guide is a dated framework rather than a standing definition, and citing the wrong edition of one is the same class of error as citing a superseded specification. CiderHQ treats BJCP as one competition framework among several and never as the universal cider taxonomy.