Raw honey is naturally shelf-stable because its water activity (aw) — the amount of "free" water available to microbes — normally sits around 0.50–0.56, far below the level osmophilic yeasts need to grow and ferment. Adding herbs, spices, fresh fruit or citrus peel introduces extra moisture from the ingredient itself. Enough of it, and the water activity of the finished jar creeps upward until it crosses the point where fermentation becomes possible — bubbling, off-flavours and gas pressure in a sealed jar.
This is a simplified teaching model, not a lab-grade predictor — real water activity depends on sugar profile, exact moisture content and mixing, so always test infused batches with a calibrated water-activity meter before selling them, and label accordingly.
A 3D jar of honey shows how adding herbs, spices, zest or fresh fruit raises the mix's water activity, and at what point that dilution crosses from shelf-stable into fermentation risk.
Fresh, wet ingredients carry far more moisture than dried ones. Blended into honey at even modest inclusion rates, that moisture pushes water activity up — and once it clears roughly 0.60, osmophilic yeasts already present in honey can start fermenting it.
Pick an ingredient, set how much of the jar's weight it makes up, and see the water-activity gauge and risk reading respond. Try drying the ingredient first, straining it out after infusing, or raising storage temperature to see how each choice shifts the outcome.
Commercial producers routinely test infused batches with a calibrated water-activity meter rather than guessing — a reading is cheap insurance against a jar that quietly builds gas pressure on the shelf.