Compound
Glucose
The sugar yeast takes first and the smallest of the three in apple juice, which is why the last sugar left in a slow ferment is almost never glucose.
Also called Dextrose.
- Class
- Sugars
- Formula
- C6H12O6
- How often it matters
- Regularly encountered
What it does in cider
- Feeds the ferment. Saccharomyces transports glucose preferentially over fructose, so it disappears from the juice first.
- Sets the early pace of fermentation, since the vigorous phase runs while glucose is still abundant.
- Contributes sweetness at roughly three-quarters the intensity of fructose for the same weight, so a juice’s sweetness depends on which sugar dominates as well as how much there is.
- Is consumed by acetic and lactic bacteria as readily as by yeast, so leaving it in a finished cider without stabilising is an invitation to refermentation.
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.
- clean sweetness
Less sweet than fructose at equal concentration, and its perceived sweetness is strongly suppressed by the malic acid alongside it — the reason a juice at over 100 g/L of sugar can still taste sharp.
Descriptors it is responsible for
Sensory records that name Glucose as a cause. Each states the perception and the mechanism behind it.
- Pressed apple juice — The full, sweet, unfermented smell of fresh juice, met in cider where residual sugar and surviving fruit esters combine.
- Baked apple — Cooked apple with a browned, Maillard-derived layer over it, met in ice cider and in long-matured sweet styles.
- Caramelised apple — Burnt-sugar sweetness over cooked fruit, from sugar breaking down under heat or high concentration.
- Raspberry — A raspberry aroma arising in unfruited cider from bacterial spoilage — the French *framboisé* — as well as from added fruit.
- Russet apple — A dry, nutty, faintly pear-like apple character associated with russeted skin and high soluble solids.
The structure it moves
| Dimension | What it is |
|---|---|
| Sweetness | How sweet the drink tastes, which is not the same as how much sugar it contains. |
| Body | How much weight and viscosity the drink has in the mouth. |
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.
Sugar10.0–30.0 g/L
context not recorded · Glucose fraction of total juice sugars · Andrew Lea
The glucose share of apple juice sugar is the smallest of the three and varies with cultivar, maturity and how long the fruit was stored before milling. It is not a measure of total sugar, which is several times higher.
Fermentable sugar available to yeast, and therefore potential alcohol. Measured in grams per litre.
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
Ripeness assessment
Judging when cider fruit has converted enough starch, loosened enough on the spur and hardened enough for the store to be worth gathering.
Sweating the fruit
Deliberately heaping or storing gathered fruit so that it softens, loses water and finishes converting starch before it goes to the mill.
Sugar addition
Adding sugar or apple juice concentrate to raise potential alcohol before fermentation, and the regulatory and compositional consequences of doing so.
What removes or limits it
Processes that reduce it, hold it below a threshold, or stop it forming in the first place.
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.
Secondary fermentation
Any fermentative event that follows the primary ferment — residual sugar refermenting, a deliberate second alcoholic fermentation, or the malolactic conversion of the maturation phase.
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.
Unwanted refermentation
Fermentation restarting in a sealed container, generating carbon dioxide that was not planned for and pressure that a bottle may not withstand.
Stuck fermentation
A fermentation that has stopped before the sugar is gone and will not restart, leaving a sweet, low-alcohol cider that is vulnerable to everything.
Bottle over-carbonation
More dissolved carbon dioxide in the bottle than intended or than the glass is rated for — a presentation problem at the mild end and a physical hazard at the severe one.
Microbial haze
Cloudiness caused by a growing population of spoilage organisms, and therefore a symptom of something worse rather than a clarity problem in itself.
Sluggish fermentation
A fermentation that is still moving but far more slowly than it should, extending the period during which the cider is weak, sweet and exposed.
Cooked character
A stewed-apple, caramel or jam-like character from heat applied to juice or cider, most often through pasteurisation or hot storage.
Ropiness
Cider that pours thick and pulls into an oily thread, caused by lactic acid bacteria secreting long-chain glucan polymers into the drink.
Starch haze
A persistent haze caused by starch carried in from under-ripe fruit, which has not yet been converted to sugar and stays suspended in the cider.
Under-carbonation
A cider intended to sparkle that has little or no dissolved gas, usually because the bottle conditioning never started or the closure did not hold.
Framboise
A raspberry-and-rotten-fruit character with sulphurous overtones, produced by *Zymomonas mobilis* in sweet ciders that still contain sugar.
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.
Zygosaccharomyces bailii
A preservative-resistant spoilage yeast that refements sweetened cider and juice, and one of very few organisms able to grow through sorbate and benzoate at cider strength.
Acetobacter aceti
An acetic acid bacterium that oxidises ethanol to acetic acid wherever cider meets air, and the organism behind most volatile acidity in cider.
About Glucose
Apple juice carries three sugars in unequal proportion, and glucose is the minor partner. It matters out of proportion to its share because yeast prefers it: Saccharomyces hexose transporters handle glucose more readily than fructose, so the two are consumed at different rates and glucose runs out first. In a healthy ferment nobody notices. In a ferment that is struggling, the distinction is diagnostic, because the sugar still sitting in a stuck cider is overwhelmingly fructose, and fructose is the harder of the two for a stressed yeast to finish.
Glucose is also the unit that starch becomes. Unripe fruit stores its carbohydrate as starch, which yeast cannot use at all; as the fruit ripens, amylases dismantle it into simple sugars. This is why a starch-iodine test is a ripeness test and, indirectly, a potential-alcohol test — the black-staining starch in an underripe apple is alcohol that has not yet become available.
For anyone stabilising a sweetened cider, the relevant fact is that glucose is universally usable. Yeast, lactic bacteria and acetic bacteria all take it. A cider back-sweetened with glucose and bottled without sterile filtration, pasteurisation or an adequate preservative will referment given time and temperature, and the pressure that follows is a genuine hazard rather than a quality problem.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Sugars
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.
Sugars
Sucrose
The disaccharide of apple juice and the sugar most often added to it, split into glucose and fructose by the yeast’s own invertase before any of it is fermented.
Polysaccharides
Starch
The fruit’s carbohydrate store, unfermentable until ripening converts it to sugar, and the reason picking early costs alcohol and risks a haze that will not clear.
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.
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.
- Why did my cider stop fermenting — The usual causes are a shortage of yeast-available nitrogen, a temperature that has dropped, too much sulphite at the start, or a yeast that has reached its alcohol limit. Check the gravity before assuming anything is wrong: many ciders simply finish.
- 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.
- 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.
- Why did my sweetened cider start fermenting again — Live yeast met the sugar that was added back. Sweetening is only stable if the yeast has been removed by sterile filtration, killed by pasteurisation, or held in check by sorbate together with sufficient sulphite.
- 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.
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.
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.