Compound
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.
Also called Glycerine, Propane-1,2,3-triol.
- Class
- Alcohols
- Formula
- C3H8O3
- How often it matters
- Regularly encountered
What it does in cider
- Balances the yeast cell’s internal chemistry early in fermentation, when it must dispose of excess reducing power before ethanol production is fully under way.
- Adds body and a slight sweetness that survives to complete dryness, so a fully fermented cider is not as thin as its residual sugar figure suggests.
- Rises when yeast is osmotically stressed — in very high-gravity juice, in ice cider, or where fruit carried Botrytis infection.
- Serves as substrate for Lactobacillus collinoides, which dehydrates it to acrolein and sets up the bitterness fault of long-stored cider.
How it is perceived
What the compound registers as, and at roughly what concentration. Perception is not a property of the molecule alone: sugar, tannin and carbonation all change where a threshold falls.
- weight
- slight viscosity
- faint sweetness
Detection in a complex drink is poor: glycerol is usually credited with more textural effect than controlled trials support, and in cider it typically sits well below the concentration at which it can be reliably picked out on its own.
Descriptors it is responsible for
Sensory records that name Glycerol as a cause. Each states the perception and the mechanism behind it.
- Beeswax — A dry, waxy, faintly sweet note from long-chain fatty acids and their esters, associated with lees contact.
- Cream — A soft, rounded dairy impression from acetoin and lactic acid without the sharpness of free diacetyl.
- Peppery bitterness — A harsh, burning bitterness from acrolein formed when lactic bacteria degrade glycerol.
- Ropy — An oily, viscous, pouring-in-a-thread texture from bacterial exopolysaccharide, with little aroma of its own.
- Soured milk — A sharp, unclean dairy note from uncontrolled lactic activity, recorded as a fault in every style.
- Yeast extract — A savoury, umami, meaty-broth note from yeast autolysis during extended lees contact.
- Bacon — A savoury smoked-meat note from 4-ethylguaiacol with residual sweetness, met in tannic ciders with Brett character.
The structure it moves
| Dimension | What it is |
|---|---|
| Body | How much weight and viscosity the drink has in the mouth. |
| Sweetness | How sweet the drink tastes, which is not the same as how much sugar it contains. |
Measured figures
Shown as they were measured, with the context each was taken in. They are not averaged: a concentration recorded in one country's fruit in one decade is not a constant.
Glycerol3.6–4.8 g/L
Villaviciosa, Asturias, Spain, 2001–2002 · 4 samples · HPLC · Suárez Valles, Pando Bedriñana, Fernández Tascón, Querol Simón and Rodríguez Madrera, Food Microbiology 24(1):25–31
Cider fermented at cellar temperature, 12–15 °C. The authors note that cold fermentation raises glycerol, so a warm ferment of the same juice would be expected to finish lower; the figure belongs to the temperature as much as to the fruit.
A fermentation by-product that adds weight and a faint sweetness without being a sugar. Measured in grams per litre.
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
Wild fermentation
Letting the microflora already present on the fruit and in the press house carry the ferment, in a succession rather than as a single organism.
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.
Ice concentration
Freezing pressed juice and drawing off the unfrozen fraction, so that water is removed as ice and everything else in the juice is left behind more concentrated.
Cryoextraction
Milling and pressing fruit that has frozen on the tree or in store, so the ice stays behind in the pomace and only concentrated juice runs from the press.
Faults it is implicated in
Being implicated is not the same as being a fault. Several of the compounds on this site are ordinary constituents of a sound cider and define a named fault only above a concentration.
Acrolein bitterness
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.
Thin body
A cider with no weight or texture in the mouth, most often from over-watered pomace, low-gravity juice or a blend with nothing to give it substance.
Film yeast growth
A pale, powdery or wrinkled film of aerobic yeast growing on the surface of a standing cider, consuming alcohol and acid and producing acetaldehyde.
Excessive astringency
A drying, roughening, mouth-puckering sensation that outstays its welcome, produced by larger phenolic polymers precipitating salivary proteins.
Flat and lifeless
A cider with nothing obviously wrong and nothing to say: aroma faded, acidity dulled, finish short — usually the cumulative result of over-processing or slow oxidation.
Organisms that produce it
Which organism is responsible usually decides whether the compound is a feature or a symptom.
Saccharomyces cerevisiae
The yeast that finishes essentially every cider, whether it arrives in a sachet or from the fruit, the press and the vessel.
Lactobacillus collinoides
A lactic acid bacterium first described from cider, and the organism most closely associated with acrolein bitterness through its conversion of glycerol.
Botrytis cinerea
Grey mould: a broad-host-range fruit rot whose laccase enzyme oxidises phenolics and whose glucans make a juice difficult to clarify.
Torulaspora delbrueckii
A non-Saccharomyces yeast that ferments further than most of its early-succession neighbours while producing notably little acetic acid.
About Glycerol
In the first hours of fermentation, before ethanol production is running freely, yeast has more reducing power than it can use and dumps the excess by making glycerol. The amount produced is therefore set by conditions at the start of the ferment rather than at the end, and it survives fermentation untouched because Saccharomyces has no reason to consume it again. A typical cider carries a few grams per litre — enough to matter alongside a residual sugar of zero, and one of the reasons a well-made dry cider has a rounder texture than the analysis predicts.
Anything that osmotically stresses the yeast pushes production up. Ice cider, where the juice may start at three times ordinary sugar concentration, ends with markedly more glycerol than an ordinary ferment; so does juice from fruit heavily infected with Botrytis cinerea, because the mould itself makes glycerol before the yeast ever arrives. Cool, slow ferments and certain non-Saccharomyces yeasts, Torulaspora delbrueckii among them, also raise it.
Its less welcome career begins in storage. Lactobacillus collinoides can dehydrate glycerol to acrolein, a sharply reactive aldehyde that then combines with procyanidins to give an intense, lingering bitterness quite unlike tannin bitterness. This is the amertume of old French and English cellar literature, and it explains why a cider can be sound at bottling and bitter two years later without any obvious spoilage having occurred.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Alcohols
Ethanol
The alcohol yeast makes from fruit sugar, which converts a perishable juice into a keepable drink and carries most of its aroma to the nose.
Aldehydes
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.
Sugar alcohols
Sorbitol
The unfermentable sugar alcohol that pears carry in quantity and apples carry only in trace, and the single reason a fully fermented perry keeps a sweetness a fully fermented cider cannot.
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 many calories are in cider — Roughly 40 to 60 kcal per 100 ml for most ciders, so a UK pint falls somewhere around 200 to 250 kcal. Alcohol contributes about 7 kcal per gram and residual sugar about 4, so both strength and sweetness matter.
- Which yeast ferments cider — Saccharomyces cerevisiae finishes almost every cider fermentation, whether it was pitched or arrived from the press house. In a spontaneous ferment it is not the first organism present, only the one that survives the alcohol it makes.
- Why is sorbitol important in perry — Sorbitol is a sugar alcohol that pears carry in quantity and that Saccharomyces cannot ferment. It passes through the whole fermentation untouched, so a perry can taste sweet while being dry by measurement.
- How does cider ferment — Yeast consumes the sugar in apple juice and produces roughly equal masses of ethanol and carbon dioxide, along with the esters and higher alcohols that give cider much of its aroma. In a wild ferment several yeast species take turns before *Saccharomyces* finishes the job.
- 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 my cider thin and watery — Thin body usually follows from dessert-fruit juice with little tannin, over-dilution, aggressive filtration, or a ferment that stripped everything out. Body in cider comes mostly from tannin, glycerol and residual sugar.
Where to go next
- All compounds — Grouped by what the fruit brings and what the ferment makes of it.
- Sensory — Every descriptor, with the compound or process that causes it.
- Microbiology — The organisms whose metabolism most of this chemistry belongs to.
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.
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.
The New Cider Maker’s Handbook: A Comprehensive Guide for Craft Producers
Claude Jolicoeur, Chelsea Green Publishing, 2013. ISBN 9781603584739 · reference work · bibliographic record verified, not opened 2026-08-25
Bibliographic record verified on 2026-08-25 against the Open Library union catalogue: Chelsea Green Publishing, 2013, ISBN 9781603584739, one edition recorded. That establishes the citation points at a real book in a stated edition, which is what a citation needs and is all it establishes. No copy was opened and nothing is quoted from it. The book itself is in print and not digitised in any open collection; where CiderHQ needs a figure from this territory it uses an accessible research source instead and says so.