Why honey never spoils: The sticky science behind the golden liquid

Honey is one of those foods that feels almost too good to be true. You can leave a jar in the cupboard for years, forget all about it, come back later, and it will probably still be fine. It might have gone cloudy or turned grainy or solid. It might even look a bit less golden than it once did, but in most cases, it hasn’t spoiled.

That is strange when you think about it; honey is sweet and microbes love sugar. Bacteria, yeasts and moulds are usually quick to move in when food gives them the chance. Leave fruit juice out too long and it starts to ferment. Open a jar of jam with a dirty spoon and you may soon get a furry surprise, but honey is different.

Honey begins as nectar, the sweet liquid that bees collect from flowers and is much waterier than honey. On its own, it wouldn’t last in the same way because it contains plenty of sugar and enough moisture to make life easier for microbes.

But bees do not simply collect nectar and store it, they process it. They pass it between bees, add enzymes, place it into honeycomb and then fan it with their wings. That fanning helps evaporate water from the nectar until it becomes thick, concentrated honey.

By the time the bees are finished, honey has become a very difficult place for most microbes to live.

Most bacteria and moulds need water to grow. Honey contains water, but not much of it is available for microbes to use, that’s because honey is packed with sugar which holds tightly onto water molecules.

Any bacteria or yeast that lands in it can have water pulled out of its cells, so, instead of feeding happily on the sugar, it struggles to survive.

Honey has another trick: it’s acidic. Not sour like vinegar, but acidic enough to make life harder for many bacteria.

Bees help create this acidity when they add enzymes to nectar. One of those enzymes helps produce gluconic acid, which contributes to honey’s flavour and its ability to resist spoilage.

Bees also add enzymes that can help produce tiny amounts of hydrogen peroxide. That may sound odd, but hydrogen peroxide is a known antimicrobial substance.

This doesn’t mean honey is some kind of miracle medicine - and different honeys vary a lot - but it does help explain why honey is so good at defending itself. It has several barriers working at once: sugar, low water, acidity and antimicrobial compounds.

One of the most common worries about honey is crystallisation. You open the jar and instead of runny golden honey, you find something thick, cloudy and grainy.

Honey contains different kinds of sugar, especially glucose and fructose. Over time, glucose can separate out and form crystals. Some honeys crystallise quickly, while others stay runny for much longer. It depends on the flowers the bees visited and how the honey has been stored.

Crystallised honey is usually perfectly fine to eat, and to make it runny again, place the jar in warm water and stir it gently. There is no need to throw it away just because it has changed texture.

Archaeologists have found traces of ancient honey in old vessels, including honey residues from Bronze Age Georgia dating back thousands of years. There are also many stories about honey found in Egyptian tombs.

Some versions of the story say the honey was still edible. That idea is possible in principle if the honey was perfectly sealed and kept dry, but it’s often repeated in a way that’s a bit too simple. The safer claim is that honey can remain preserved for an astonishingly long time when the conditions are right.

Yes, but it usually needs help.

If moisture gets into the jar, the balance changes. A wet spoon, a loose lid, a humid kitchen or honey that was harvested with too much water in it can all make fermentation more likely.

When that happens, sugar-loving yeasts can start to wake up. The honey may smell sour, boozy or fizzy. You might see bubbles, foam or pressure building in the jar. At that point, the honey has started to ferment.

But here is the funny part: honey going “off” is not always a disaster. Give honey enough water, add the right yeast, and control the process properly and you get mead - the ancient alcoholic drink made from fermented honey.

Keeping honey in good condition is simple. Store it in a clean, dry jar with the lid tightly closed and keep wet spoons out of it. Do not add water unless you are deliberately making something fermented. Room temperature is fine, and refrigeration is unnecessary.

If it crystallises, warm it gently. If it smells alcoholic, sour or starts bubbling, fermentation has probably begun.

There is also one important safety note: honey shouldn’y be given to babies under 12 months old. It can contain spores of Clostridium botulinum. These spores do not normally grow in honey, but they can be dangerous for infants