A reader asked this question yesterday and I thought it was worth writing about. Sugar syrup will mold very quickly, especially in the physical conditions of the hive. A white, fluffy growth may be seen in just a few days. A small amount of mold doesn’t seem to bother the bees, but if it gets thick and smelly the syrup should be discarded.
Beekeepers have come up with many methods to combat mold in syrup. One of my favorites is the baggie feeder because it severely limits the amount of syrup exposed to the air, and since the bees drink only from the slits in the bag, the syrup in those areas is quickly consumed.
Honey-B-Healthy contains essential oils which inhibit mold growth. This commercial product is effective because the emulsifier allows the oils to be blended into the syrup. Simply adding essential oils to syrup doesn’t work because the oil floats to the surface and accumulates in puddles, much like an oil spill in the ocean.
If you want to try making your own emulsion, the following recipe is used by some beekeepers for spring syrup:
- Heat 5 quarts (5 l) of water to nearly boiling and then add ½ teaspoon (2.5 ml) lecithin granules. (Lecithin is the emulsifier.)
- Stir until the lecithin is dissolved. (This may take a while; it tends to float.)
- Once the lecithin is dissolved, remove the water from the heat and add 10 pounds (4.5 kg) of granulated white sugar. Stir until dissolved.
- Add 1 teaspoon (5 ml) essential oil and stir thoroughly.
Lemongrass oil is reputed to have strong antifungal action. You can also use a combination of half lemongrass oil and half spearmint oil.
Other beekeepers prefer to use distilled apple cider vinegar or lemon juice. Both of these decrease the pH (increase the acidity) of the syrup. Honey is relatively acidic with a pH range of about 3.2 to 4.5 so bees tolerate the increased acidity very well while most molds do not. I have not tried this method, but I’ve read that 2 to 4 tablespoons/gallon of syrup is commonly used. Since the pH of water varies tremendously to start with, it is impossible to guess how much will be needed for any one water supply. If I were to try this method, I would start with the lesser amount and see how that worked.
Cream of tartar (related to tartaric acid but not the same) is sometimes used to increase acidity, but most beekeepers today stay away from it because of reports that it can cause bee dysentery.
All these methods can work to slow mold accumulation but none of them will stop it completely. If you have consistent mold problems, you may have to feed less syrup at each feeding so it is used up quickly.