1. Honey Is Very Dry: Only About 20 Percent Water
The main components of honey are two types of sugar, glucose and fructose, and water. The water content is generally around 17 to 20 percent. In Japan, fair competition rules set the limit at 20 percent or less, though domestic honey is allowed up to 22 percent [1]. The Japan Beekeeping Association also sets a standard for domestic natural honey at 22 percent water or less at 20°C [2].
Another interesting fact is how easily honey absorbs water. A Japanese review paper states that honey with 17.4 percent water balances with air at 58 percent humidity, while honey with 21.5 percent water balances with air at 66 percent humidity [3]. This suggests that if honey is exposed to air more humid than the level corresponding to its water content, it tends to absorb water. Molds and many bacteria do not grow well in places with little water. Honey, being a low-water food, fits this condition closely [3].
2. Honey Is Acidic: It Is More Sour Than Flower Nectar
Honey is an acidic food. The average pH is 3.9, with a range of 3.4 to 6.1 depending on the type [4]. pH is a measure where lower numbers indicate stronger acidity. A Japanese review notes that in one example, flower nectar has a pH of 5.1, but it becomes 3.7 when it turns into honey [3]. While this is just one example, it aligns with English sources suggesting that nectar becomes more acidic as it transforms into honey. An acidic environment is explained as one reason bacteria struggle to grow [4]. But where does this acid come from?
3. Enzymes From Bees Add Acid: How Glucose Oxidase Works in Nectar
The main cause of the sourness is an enzyme from bees called glucose oxidase. When this enzyme acts on the glucose in nectar, it creates two substances: gluconic acid and hydrogen peroxide. Gluconic acid is one reason honey is acidic, and hydrogen peroxide helps inhibit the growth of bacteria [4]. Interestingly, a paper notes that this enzyme is in an active state within the nectar, but becomes active only when the honey is diluted with water. In thick, undiluted honey, hydrogen peroxide does not increase much [5].
Around 1937, researchers named a substance in honey that stopped bacterial growth "inhibin." Later, White and others showed that this substance was the hydrogen peroxide produced by the enzyme [3]. The authors of the review conclude that the suppression of bacterial growth is likely due not just to high sugar concentration and low pH, but also to the production of hydrogen peroxide [3].
4. When Honey Can Spoil: Extra Water Lets It Ferment
Honey can ferment if water increases. According to a Japanese review, fermentation depends on moisture content and temperature. If moisture is 19 percent or higher, it will eventually ferment, and it ferments more easily at temperatures above 10°C. Fermentation causes bubbling, produces alcohol, and then acetic acid, making it sour. This change happens very slowly and often occurs after crystallization [3].
English sources explain that honey is practically shelf-stable indefinitely if moisture does not significantly exceed 18 percent, but fermentation begins easily if it significantly exceeds about 25 percent [4]. The difference in numbers compared to the Japanese figure of 19 percent may be due to different dates, yeast amounts, or temperatures in the studies. Here, we focus on the main idea: more water makes fermentation more likely. Crystallization also needs attention. Honey crystallizes because some sugar components harden. Rules and standards note that honey may crystallize [1][2]. When partial crystallization occurs, water collects in the liquid part, making that area more prone to fermentation [3].
5. Was Ancient Egyptian Honey Really Preserved? Why Keeping Water Out Matters
The story that "jars of honey thousands of years old were found in ancient Egyptian tombs" is widely known. A magazine article mentions archaeologists finding jars of honey in tombs that were still preserved [6]. However, while stories of finding jars exist, whether edible honey was actually excavated is often just what is reported. In a magazine interview, immunologist Amina Harris lists three reasons for this longevity: low moisture, a pH of around 3 to 4.5, and hydrogen peroxide. She says, "If you keep the lid on and do not add water, honey will not spoil. If you add water, it may spoil" [6]. Thus, honey's resistance to spoilage comes with the condition that it remains dry.
6. How to Investigate Honey Further: Checking the Jar and Label at Home
Try observing the label and the inside of the lid of the honey jar at home. Check the origin, any moisture information on the label, if there are crystallized parts, and if there are bubbles or a sour smell. Do this together with an adult. If the honey is crystallized, see whether fermentation may have started in that part. If you have a crystallized jar, compare it with an adult to see if the non-crystallized part remains smooth and free of bubbles or odors. For those who want to read more, the Japan Beekeeping Association's "Quality Standards" page briefly summarizes rules like moisture standards [2].