Most of the natural food material whether it is from animal or plant origin quickly deteriorates due to microbial interaction. The nectar from flowers, vegetables, fruits, grains, verities of fish, meat etc all will deteriorate the only difference among them is the time taken for it is different. However the sweet “honey” is something of an oddity, it doesn’t spoil over time. The oldest known sample of honey, found in an Ancient Egyptian tomb dated back to approximately 3000 years was still found to fresh as extracted a few days back. What is the reason for unusual property of Honey?
Honey is derived from plant nectar, by the action of honey bees, sometime called as nature’s chemists. The nectar composition varies from plant to plant; the dominant component is the sugar sucrose or its hydrolysed product glucose and fructose in almost 70% water. Workers bees will collect the nectar from flowers, and store it in their honey stomach – distinct from their normal stomach. Enzymes mainly invertase secreted from their glands initiate the breakdown of the sucrose in the nectar to simpler sugars. Once the worker bee returns to the hive, it will regurgitate the nectar solution and pass it on to one of the house bees, who remain in the hive. The house bees will continue the hydrolysis process for up to 20 minutes, it will regurgitate and re-drink the nectar, whilst some sucrose will remain and the majority is broken down into glucose and fructose.
Once suitable breakdown has been achieved, the house bee deposits the nectar into the honeycomb in the hive; however it will not be stable with the large percentage of water present in it. The bees fan the nectar with their wings and the water content of the solution will drop to around 17% within three days eventually, the watery nectar converted to syrupy honey.
The very low water content of honey is a key factor for its long shelf life. The water content is much lower than that of bacteria or fungi, so that the water migrates from their body making them dry and eventually the death. Honey also has a low water activity; that is a measure of the amount of water in a substance that is available to support microbial growth. Water activity scale is of 0 to 1, honey has a water activity of 0.6 much lower than 0.75 the level at which most moulds and bacteria were unable to grow.
Another factor that helps honey avoid spoiling is its acidity with an average pH around 4; majorly due to presence of gluconic acid, the oxidized product of glucose by the action of bee enzymes. Honey may contain other acids like formic acid, citric acid, etc depending on the source of nectar. Common bacteria thrive to grow at neutral pH or near to pH 7. Hydrogen peroxide is also produce by the production of gluconic acid which further boosts honey’s antibacterial properties.
However a few reported the spoiling of honey, how?
The honey’s is a super-saturated solution of sugar in water so that over time, honey tends to crystallise and solidify there by increasing the water content in the liquid phase. This honey solution may spoil due to higher water activity.