Science Monday: Why Does Honey Last (Literally) Forever?

Sam Westreich, PhD
May 11 · 6 min read

3,000 year old honey, from the tombs of pharaohs, is still edible. How can a food last thousands of years without spoiling?

honey dripping from a wooden utensil held between fingers
honey dripping from a wooden utensil held between fingers
“Yeah, this is some good bee goop, right here. Can’t wait to leave this out on the counter for 2,000 years, and then eat it. Sounds like a good plan to me.” Photo by Arwin Neil Baichoo.

What’s the oldest food that you’ve ever eaten? If you look in your fridge and cupboards, what food has been in there the longest? Would you still consider it safe to eat?

Ignoring spices and some condiments, most of the food in my house is less than two years old. There are a couple tins of canned meat that are probably still safe to eat, despite being purchased a few years ago, and it’s hard to ever imagine a box of kosher salt actually “going bad.” I wouldn’t feel much concern over adding a splash of year-old soy sauce to my food, or eating some canned food from a couple years ago (as long as it was still in a sealed can, of course).

But what about food that was way, way older?

What if that bit of food was more than 3,000 years old?

If you were an archaeologist exploring a pyramid, and you found some of the pharaoh’s preserved snacks, would you feel comfortable taking a bite (putting aside the whole “damaging a dig site and destroying ancient artifacts” angle)?

For almost any food, I’d turn down the chance to eat a 3,000 year old sample.

But if we’re talking about honey, on the other hand…

Honey is one of the very few foods that lasts forever.

How?

Honey, Delicious Bee Puke That’s Great On Toast

First off, where does honey come from? How is it made?

Honey is made by bees, and starts with sweet nectar that’s produced by flowers. Flowers produce nectar, a sugar-rich liquid, in order to attract insects to visit. While insects are greedily lapping up this sugary nectar, they accumulate bits of pollen, a fine dust that contains the plant’s genetic material. Once the insect moves on to the next flower, some of the pollen from previous flowers is deposited.

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Pictured: nectar slut, pickin’ up all kinds a’ pollen. Photo by Dmitry Grigoriev.

In other words, nectar is just the bait that lures insects, so they’ll track the pollen from flower to flower and spread the plant’s genes. Nectar is the “free appetizer with any order” that might be offered at a restaurant, in order to lure in patrons so they’ll buy a meal.

Bees are eager to consume this nectar — but they don’t burn all of it for energy inside their little bee bodies. Instead, they store most of it in their “honey stomach,” carrying up to half their weight in nectar back to the hive!

Back in the hive, worker bees repeatedly regurgitate (spit up) the nectar, blowing bubbles to evaporate the water. They also mix it with their digestive enzymes, which break down the sugar, starch, and protein in the nectar, making it more acidic.

Once the nectar has thickened and gone through this process, the bees deposit it into honeycomb, where it continues to get thicker as more water evaporates. Once it’s mostly evaporated, the bees add caps to the honeycomb to seal the honey inside, ready for later consumption by larvae or by adults when food is scarce.

This is where humans come in, literally. Beekeepers remove some of the honeycomb from hives, slice it open, and spin it to extract the thick, liquid gold from inside. They filter out any beeswax or other debris, pour it into bottles, and voila! Honey!

It’s weird to think about how we get this food, but it’s undeniably delicious — and used in many foods, including meats (honey baked ham), desserts (honey cakes), as a spread on bread, and even for fermented drinks (honey mead).

But why doesn’t it spoil?

Honey, You Gonna Last Forever (If Kept Away From Moisture, Baby)

There are three secrets to why honey doesn’t spoil: its acidity, its sugar-to-water ratio, and its antimicrobial properties.

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Acid: despite its bright and cheery color, not a preferred home for bacteria. Photo by Alex Kondratiev.

Acidity

First, let’s talk about the acidity. Most bacteria prefer to grow in neutral conditions, neither acidic nor basic. In acidic conditions, many of the basic proteins that make up the molecular machines inside cells break down.

The enzymes that bees use to break down the sugar in honey also makes it more acidic, making it less appealing for bacterial growth.

Sugar content

Second, honey has a lot of sugar — but very little water, thanks to the bees’ work to evaporate most of it to thicken the nectar. In fact, honey has so much sugar that it’s hygroscopic — that is, it has the ability to absorb water out of the air!

Think about that box of baking soda that’s probably somewhere in your house, maybe in the back of your fridge. Ever notice how the powder forms clumps after a while? That’s because the powder absorbs water from the air, especially in humid conditions.

Honey is the same way. Honey normally contains around 18% water, which isn’t enough for most bacteria to grow. They’re trapped in a desert! It’s only if more water is added, such as if the honey is exposed to humidity, that bacteria will eventually be able to grow. Once the water content rises above 25%, bacteria may grow — this is why it’s important to keep a container of honey closed.

Antimicrobial compounds

Third, there are a couple molecules in honey that fight bacteria.

The first is hydrogen peroxide, which is produced as a product of some of the enzymes used by bees to digest the more complex sugars. Hydrogen peroxide breaks down the cell walls of bacteria.

But some honey types also contain other antimicrobial compounds, such as defensin-1, an antibiotic that bees produce as part of their immune system. For millennia, honey has been used to treat wounds as an antiseptic, but now researchers are starting to look towards honey as a potential source of new antibiotics.

Combined, these properties — acidic, low moisture content, and antimicrobial compounds — mean that honey is incredibly stable and, as long as it’s not exposed to outside moisture or humidity, won’t change or degrade.

So, what’s the oldest honey around?

Thanks to preserved samples of beeswax, we know that humans and bees have been interacting in some form for more than 9,000 years — but until 2003, the oldest collected, preserved samples of honey are about 3,000 years old, from inside ancient Egyptian pyramids. In 2003, archaeologists uncovered honey samples from the country of Georgia that dated back 4,700–5,500 years.

Given that these discoveries are important artifacts, no one’s going to be spreading these samples on toast — but it’s amazing to think that tiny insects produce one of the very few foods that can last for thousands of years without degrading.

Honey can spoil — if it absorbs too much water. Be sure to keep any honey on hand in a sealed container. It may also change color or crystallize, but this is fine, as long as the moisture level stays low.

That’s some sweet knowledge, right there.

Sam Westreich holds his PhD in genetics, focusing on methods for studying the gut-associated microbiome. He currently works at a bioinformatics-focused startup in Silicon Valley. Follow on Medium, or on Twitter at @swestreich.

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Sam Westreich, PhD

Written by

PhD in genetics, bioinformatician, scientist at a Silicon Valley startup. Microbiome is the secret of biology that we’ve overlooked.

The Startup

Medium's largest active publication, followed by +717K people. Follow to join our community.

Sam Westreich, PhD

Written by

PhD in genetics, bioinformatician, scientist at a Silicon Valley startup. Microbiome is the secret of biology that we’ve overlooked.

The Startup

Medium's largest active publication, followed by +717K people. Follow to join our community.

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