Reviewed by Elena P. · Last Updated September 29, 2026 · How we review
Fermented honey smells sour, yeasty or winey, keeps forming foam or fine bubbles after you skim or stir it, and often pushes up its lid. It is usually runnier than it should be, and in a partly granulated jar the fermenting part is the wet liquid layer on top. Any one of these signs alone can have an innocent explanation, so the reliable way to identify fermentation is to look for two or more of them together and then rule out the common lookalikes.
This guide covers the signs in the three places beekeepers and honey buyers actually find fermenting honey (in the comb, in a bucket or drum, and in a jar), the four lookalikes that get mistaken for it, and how a moisture reading or a lab test turns a suspicion into a diagnosis.
Key Takeaways
- The core signs are a sour, yeasty, beery or vinegar smell, foam or bubbles that keep coming back, gas pressure under the lid, and a thinner, runnier texture.
- Fermentation is caused by sugar-tolerant (osmophilic) yeasts that are present in all honey but can only grow when the honey is too wet, typically above about 17 to 19% moisture.
- Air foam from bottling, granulation “frosting,” wax and pollen scum, and small hive beetle slime can all look like fermentation. Smell and whether the foam returns are the fastest ways to tell them apart.
- A refractometer reading confirms the cause: honey below 17.1% moisture is very unlikely to ferment, and honey above 19% can be expected to ferment within a year, according to USDA figures.
- Honey that has begun to ferment does not meet the international Codex honey standard, so it should not be sold as table honey, though lightly fermented honey is often still usable for cooking or mead.
Table of Contents
- The Six Signs of Fermented Honey
- Signs by Where You Find It: Comb, Bucket, or Jar
- Four Lookalikes to Rule Out First
- How to Confirm It: Moisture Reading and Lab Tests
- Why Honey Ferments, in Brief
- How Far Has It Gone? Early, Active, and Advanced
- What to Do Once You Know
- Frequently Asked Questions
The Six Signs of Fermented Honey
Check these in order. The first two are the most telling, and they take less than a minute with the lid still on the jar or bucket.
- Smell first. Open the container and smell before you stir. Fermenting honey smells yeasty, like bread dough or beer, or winey and slightly alcoholic. As it goes further, it picks up a sharp vinegar note, because acetic acid bacteria convert the alcohol to acetic acid when oxygen is present. Normal honey, even dark or strongly flavored honey, smells of flowers, caramel, or malt, never of yeast or vinegar.
- Foam that comes back. A layer of fine, off-white foam or froth on the surface is common. The telling part is that it keeps re-forming after you skim it, and that small bubbles keep rising through the honey days or weeks after bottling, when any air trapped during extraction should long since have risen out.
- Pressure. A domed lid, a bulging plastic bucket or pail, a hiss when you loosen the cap, or honey that wells up out of the opening are signs of carbon dioxide building inside. In commercial storage the same thing shows as drums with rounded ends, and honey gushing out when the cap comes off.
- A thinner texture. Fermenting honey is often noticeably runnier than it was when you packed it, or runnier than other honey from the same harvest. That is both a cause and an effect: extra water lets yeast grow, and the growing yeast produce more liquid.
- A liquid layer on granulated honey. In a jar or bucket that has only partly set, look for a runny layer on top of the crystals. That layer is wetter than the original honey, and it is where fermentation usually starts, so smell it specifically.
- A sour, fizzy, or boozy taste. If the smell is borderline, a small taste settles it. Fermented honey tastes tangy or sour behind the sweetness, sometimes with a faint prickle on the tongue from dissolved carbon dioxide.
One sign on its own is a reason to look closer, not a verdict. A foamy surface with a normal honey smell is usually just air. A sour smell plus foam that returns plus a domed lid is fermentation.
Signs by Where You Find It: Comb, Bucket, or Jar
Most guides describe only a jar on a kitchen shelf. Beekeepers meet fermentation in three different settings, and it looks different in each.
In the comb, before extraction
Fermentation can begin in the hive or in stored supers, almost always in uncapped cells, where the bees have not finished drying the nectar. The US BeeMD diagnostic key lists the field signs as excessively liquid honey, honey running out of the comb cells, and a smell of spoilage when you open the colony or the honey container. Up close, fermenting cells look full of tiny bubbles instead of clear, glassy honey, and in heavier cases foam oozes out of the cells and collects on the bottom bars or under the frames.
Weak colonies and stored supers left on or off the hive too long are the usual settings. If you see this, check the frames closely for small hive beetle larvae before assuming it is simple fermentation (see the lookalikes below).
In a bucket, pail, or drum
Bulk honey shows fermentation mainly as pressure and surface change: a lid that bows upward, a foamy or crusted top layer, a separated liquid layer on granulated honey, and a sour or alcoholic smell as soon as the lid lifts. A 2018 New Zealand Beekeeper article by Steve Howse of Analytica Laboratories, drawing on USDA data, describes drums with rounded ends and honey gushing out when the cap is removed as the telltale signs in bulk storage. Buckets kept in a warm garage or shed through summer are the classic case.
In a jar
In retail or kitchen jars, watch for a domed or popped lid, persistent fine bubbles streaming up through the honey, a foam ring that returns after you wipe it away, honey seeping around the lid threads, and the sour or winey smell when the jar is opened. A jar that was bottled weeks ago and is still getting more bubbly, not less, is the clearest jar-level warning.
Four Lookalikes to Rule Out First
Most “is my honey fermented?” worries turn out to be one of these. The two questions that separate them fastest are: does it smell sour or yeasty, and does the foam come back after you remove it?
| What you see | Fermentation | Harmless or different cause | How to tell them apart |
|---|---|---|---|
| White foam on top of a new jar | Foam keeps re-forming; bubbles keep rising for weeks; sour smell | Air foam from extraction and bottling rises to the top in the first days and stops | Skim it. Air foam does not return and smells like normal honey. See foam on honey after bottling. |
| White streaks or patches on the glass | Rarely looks like this | Frosting: normal granulation pulling slightly away from the glass | Frosting is dry, feathery and fixed in place, with no smell change and no bubbles. See granulation vs fermentation. |
| Scum or specks on the surface | Foamy, bubbly, often off-white | Wax, pollen, and debris floating up from lightly strained honey | Debris is flecked and particulate, sits still, and does not fizz or smell sour. |
| Frothy, runny honey in the hive or honey house | Yeasty or winey smell; honey intact otherwise | Small hive beetle slime-out: beetle larvae and their frass make honey ferment and froth | Look for white larvae and slimy, weeping comb. The University of Georgia Bee Program notes that beetle-fermented honey smells like rotting oranges. See small hive beetle slime-out. |
The beetle case matters most, because it is a pest problem in the hive, not a storage problem in the jar, and it needs a different response. Honey from a beetle slime-out should never be fed back to colonies.
How to Confirm It: Moisture Reading and Lab Tests
Smell and foam tell you something is happening. A moisture reading tells you why, and whether the rest of the same batch is at risk.
Take a refractometer reading
Put a drop of the suspect honey on a calibrated honey refractometer (if the honey is granulated, test the liquid layer, since that is where the water collects). Our step-by-step guide to testing honey moisture with a refractometer covers calibration and temperature correction.
USDA figures from Beekeeping in the United States (Agriculture Handbook 335), as summarized in the New Zealand Beekeeper article above, give the working thresholds:
- Below 17.1% moisture: honey will not ferment within a year, even though yeast is present.
- 17.1 to 19%: risk rises with moisture and with the number of yeasts in the honey.
- Above 19%: honey can be expected to ferment in the year after harvest, even with low yeast levels.
For comparison, the USDA’s extracted honey grade standards require 18.6% moisture or less for Grade A. A reading above about 19% on a jar that smells sour is a confirmed diagnosis. A reading below 17% on a jar that smells normal means the foam or bubbles you saw almost certainly have another cause. For a band-by-band risk table, see what causes honey to ferment after bottling.
When to use a lab
For bulk honey you plan to sell or store for a long time, a lab can run an osmophilic yeast count, which targets only the sugar-tolerant yeasts that can grow in honey. Howse’s article gives these benchmarks: more than 100 yeasts per gram is high, more than 1,000 per gram is very high, and even 10 per gram is a meaningful risk if moisture is above ideal. Labs can also measure ethanol or acidity if you need documented proof that a batch has started to ferment, for example in a dispute with a buyer.
Why Honey Ferments, in Brief
All honey contains dormant osmophilic yeasts, picked up from flowers, the hive, and extraction equipment. At normal moisture, honey is too concentrated for them to grow. When the water content rises, they start converting sugars into alcohol and carbon dioxide, and with oxygen present the alcohol then turns to acetic acid. The usual reasons honey ends up too wet are harvesting uncapped frames, extracting or storing in humid air, and partial granulation, which leaves a wetter liquid layer behind.
Temperature decides the speed. According to the New Zealand Beekeeper summary, yeast growth in honey occurs between about 10 and 27°C (50 to 80°F), which covers most room and shed storage. Below 10°C, fermentation stops, but only while the honey stays that cold. The full list of causes is covered in what causes honey to ferment after bottling, and the harvest side in ripe honey moisture content.
How Far Has It Gone? Early, Active, and Advanced
Once you are sure it is fermentation, how far it has progressed decides what the honey is still good for.
| Stage | What you notice | What it usually means |
|---|---|---|
| Early | Faint yeasty or fruity note, a few persistent bubbles, lid only slightly domed, taste mostly normal | Caught in time; stopping it now keeps most of the flavor |
| Active | Clear sour or winey smell, foam that returns daily, obvious lid pressure, runnier honey | Flavor already changed; not sellable as table honey, often fine for cooking or mead |
| Advanced | Strong vinegar or alcohol smell, heavy froth, seeping or gushing containers, any mold | Largely spoiled; discard anything with mold or off, solvent-like smells |
What to Do Once You Know
First, move the container somewhere cold (below about 50°F) to pause the yeast while you decide, and loosen the lid slightly so pressure can escape. Then:
- To stop it and salvage what you can, including heat treatment and the best uses for lightly fermented honey, follow can fermented honey be saved.
- If you sell honey, take affected batches off sale. The Codex Alimentarius honey standard states that honey “shall not have begun to ferment or effervesce”. In the US, the extracted honey grade standards require Grades A, B, and C alike to be free from objectionable flavor caused by fermentation, so noticeably fermented honey fails even Grade C (more in our guide to USDA honey grading).
- Check the rest of the batch. Jars filled from the same bucket share the same moisture, so test and smell them too.
- Prevent a repeat with the steps in how to prevent honey fermentation, including its fermentation risk checklist before bottling.
Fermenting honey on purpose is a different subject. If you are making fermented garlic honey or other honey ferments, see honey fermentation and its uses, and for honey wine, our guide to making mead from your own honey.
Frequently Asked Questions
What does fermented honey smell like?
It smells yeasty, like bread dough or beer, or winey and faintly alcoholic. In later stages it develops a sharp vinegar smell as acetic acid forms. Normal honey smells floral, caramel-like, or malty and never has a yeast or vinegar note.
Is foam on top of honey always a sign of fermentation?
No. Most foam on newly bottled honey is air that was whipped in during extraction and bottling, and it rises to the top within a few days. If you skim it and it does not come back, and the honey smells normal, it is not fermentation.
Why is the lid on my honey jar bulging?
A domed lid means gas is building inside, which in honey almost always means yeast is producing carbon dioxide. Smell the honey when you open it; a sour or winey smell confirms fermentation. Move the jar somewhere cold and loosen the lid slightly.
Can honey ferment in the comb before it is extracted?
Yes. Uncapped, unripe honey can ferment in the hive or in stored supers, showing bubbly cells, foam oozing from the comb, runny honey leaking from cells, and a sour smell. Always check for small hive beetle larvae too, since beetle activity causes the same frothing.
Is fermented honey safe to eat?
Lightly fermented honey is not generally considered dangerous, but its flavor has changed and it should not be sold as honey. Discard any honey with mold, a strong solvent-like smell, or heavy froth. As with all honey, do not give it to infants under 12 months old.
Can I feed fermented honey back to my bees?
It is best avoided, especially in large amounts, because of the alcohol it contains. Never feed back honey from a small hive beetle slime-out, which carries the beetles’ yeast and larvae with it.
Does crystallized honey mean it has fermented?
No. Crystallization is a normal physical change and does not affect safety or flavor. However, a jar that has only partly crystallized has a wetter liquid layer on top, and that layer can ferment, so smell it and check it for bubbles.
Image credits: Photo: Einebillion, CC BY 4.0.
