Why does honey rarely spoil?

Answer

Few microbes survive in it. Sealed honey can stay edible for a very long time.

Context

Mature honey is a concentrated sugar solution. Typical honey has a water content of roughly 17 to 18 percent, with most of the rest made up of the sugars fructose and glucose. Such a mixture is strongly hygroscopic and has low water activity, which means that microbes that land in it lose water to the sugar and cannot grow. This osmotic effect is probably the most important protection.

Honey is also acidic, with a pH commonly reported at around 3.5 to 4.5, due to organic acids such as gluconic acid. The acid is produced by an enzyme from bees, glucose oxidase, which converts glucose to gluconic acid and also forms hydrogen peroxide. The peroxide is made mainly when honey is diluted, so its role in sealed, undiluted honey is smaller than the popular summary suggests. Reviews of the topic also point to other antibacterial features, including plant-derived compounds and, in some honeys such as manuka, additional non-peroxide activity.

The practical result is that sealed honey stored away from moisture can stay free of spoilage for very long periods. Popular accounts mention edible honey in ancient Egyptian tombs; such stories are widely repeated but are hard to verify, so they should be taken as anecdotes. Honey can still change. If it absorbs moisture, wild yeasts can ferment it, and it often crystallizes as glucose separates out, which affects texture but is not spoilage. Infant botulism is a recognized concern linked to honey because of bacterial spores; this is a reported finding, not guidance.