Hydroxymethylfurfural (HMF) is a naturally-occurring organic acid with the formula C6H6O3. It is often formed during the dehydration of sugars, especially fructose, and is known to be toxic to honey bees.
Much has been written during the past few years about the occurrence of HMF in high-fructose corn syrup* (HFCS), but that is certainly not the only place where it is found.
Regular table sugar (sucrose) is a disaccharide, meaning it is composed of two monosaccharides. In the case of sugar, those monosaccharides are glucose and fructose. Sugar is easily broken down into its components parts. The process is called inversion, and the resulting product is called invert sugar. Once the sugar is inverted, the fructose portion can dehydrate and form HMF.
Honey bees do it with invertase
The honey stomach contains invertase, an enzyme that inverts sucrose into glucose and fructose. Invertase by itself does not increase the production of HMF. However, the inverted product becomes acidic because the fructose donates a proton during the reaction and thus behaves like an acid.
The production of HMF from fructose can be enhanced in a number of ways. Heat, for example, increases the production of HMF. Honey that was heated contains more, HFCS that was heated contains more, and sugar syrup that was heated contains more. Acids that are used to invert sugar also speed up the process. Citric acid, vinegar, or cream of tartar (potassium bitartrate) added to sugar syrup can rapidly increase the formation of HMF. And time alone can increase HMF as well. Old HFCS contains higher levels of HMF, as does old honey.
High HMF equals high mortality
You can find many articles detailing the numbers, but basically the higher the HMF levels, the higher the bee mortality. Low levels of HMF may be such that we can’t easily recognize the increased mortality. For example, if you have a 10-15% bee mortality due to HMF, you may not notice it. But if you couple that with mortality due to mites or a pathogen, the extra bee deaths may be enough to push the colony over the edge.
I can’t say that I ever noticed extra bee deaths when I was feeding cooked fondant. I switched to uncooked sugar several years ago out of sheer dislike for the process. But when I look at the science behind the production of HMF, I can’t see any reason for heating sugar. Why take the risk? Bees are equipped to invert the sugar themselves without producing HMF.
On the other hand, is feeding old honey worse than feeding newly cooked fondant? The answer is a moving target—a complex subject with no easy answers.
Isn’t the pH of sugar bad for bees?
Related to the discussion of HMF is the often heard admonition that feeding syrup or granulated sugar is bad because the pH of sugar is about 7 (neutral) whereas the pH of honey is down around 3 or 4 (quite acidic). This argument assumes that the pH of nectar is the same as the pH of honey, but I don’t believe that is a safe assumption.
When bees process sugar syrup, they treat it like nectar, adding enzymes, storing it, and drying it. So the pH of syrup should be compared to the pH of nectar, not the pH of honey (the finished product).
Since many nectars contain sucrose, it is most likely that honey bees will make the nectar more acidic by inverting the sucrose, just as sugar syrup
becomes more acidic after inversion into glucose and fructose. I don’t know the pH of nectar, although I assume there is a wide range. But the pH of nectar is the number we need to know before we can conclude that the pH of sugar is somehow harmful to bees.
*LeBlanc, B. W.; Eggleston, G; Sammataro, D; Cornett, C; Dufault, R; Deeby, T; St. Cyr, E (2009) Formation of Hydroxymethylfurfural in Domestic High-Fructose Corn Syrup and Its Toxicity to the Honey Bee (Apis mellifera). Journal of Agricultural and Food Chemistry 57: 7369-7376
Honey Bee Suite