feeding bees

Hydroxymethylfurfural in sugar syrup

HMF molecule png

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

HMF molecule png

HMF molecule



  • Good to know. This fall I fed a swarm that was a little light and I added a little lemon juice to the heavy syrup to bring the acidity down, as an experiment. It would be worth getting some ph measurements of various stages of unripe honey for future experiments.

  • I am confused. Should i just leave cane sugar in its natural state in a bowl when my bees need feeding, or make a 1:1 syrup? which is better?

  • So disappointed. You don’t know the ph of nectar? You’re slipping, Rusty. Lazy, lazy, lazy.

    Come on. If you’re going to advise and entertain the world you need to do ALL our work for us, not just most of it.

    I’ll sit and wait while you research it. Let me know when it’s ready.

  • Sigh…I waited 15 minutes and you didn’t reply. Hopeless.

    So I did some research. It is jolly interesting. I found one person from Lincolnshire (I corrected her terrible northern spelling):
    oliver90owner Queen Bee says “Nectar is 2.7 – 6.4. There will always be a range but three to four is typical.”

    I have no idea if she knows what she is talking about but Michael Bush discusses it at length and he does tend to know an awful lot. He doesn’t answer the question though, as far as I can tell. Instead, he seems to say (these are not his words) “Get a tester for your own nectar because it varies from place to place and during any one season” which, if you think about it) is blindlingly obvious. And testers are super cheap and testing is super easy. So, bingo, we can now make perfect winter food that takes account of invetase and the whole problem.

    Oh but hang on…

    If we start from the premise that feeding is a bad idea unless the bees are actually going to die if you don’t (and even then, there is an argument that fitter bees can only come from survival of the fittest) and if we assume that bees and nature generally knows best, then surely you have to be right that nectar is the ph to match.

    But is matching ph the only factor? It seems to me that messing about with ph tester strips cut to fit the cells of nectar, taking an average across the frame and then the hive, laying out syringes of carefully measured vinegar and other acidifiers/alkaliners and spending hours getting the ph of our syrup perfectly in line with the seasonal nectar may have knock on effects that we really can’t understand unless we wear a white coat and numerous pairs of glasses. Is it really a good idea?

    Maybe ph isn’t the only balancing factor. And maybe that’s why Michael doesn’t answer the question. Maybe the answer is a little too complex to let loose on a world of eager beekeepers who do tend to latch onto half-baked ideas and poor science and then recommend it to anyone with slightly less experience than them?

    • Richard,

      Thanks. I always think about amino acids in pollen, but never give much thought to how many are in nectar. Good article.

  • Wow. Complicated stuff. Do I understand correctly that you make sugar syrup by just letting sugar dissolve in cold water?

    A few years ago I tried to find out (online) the pH of nectar for the purpose of adding something to sugar syrup to bring its pH closer to that of nectar. I forget the details of what I was able to find out (probably variable, as you say), but the upshot was that while I was already adding lime juice to syrup to prevent mold, I was now also adding it to bring its pH closer to nectar’s, at least on average. After reading your article, I’ll quit doing that.

    Thanks for the info!

  • Since heated sugar produces HMF, are we damaging our bees by feeding 2:1 sugar syrup in the fall? Would 1:1 syrup be safer? How hot does the sugar temperature need to be in order to produce HMF? This summer I am planning on extracting less and freezing a lot more frames of honey and putting them back on the hives as winter sets in.

    • Angie,

      It increases with the amount of heat, but it doesn’t take much. I will try to find a chart of values that I can post. As I told another reader, I’ve been feeding 1.5:1 syrup in the fall because I can dissolve it without any heat.

  • Wish I’d a known that before I went to the work of making candy boards. So a pile of sugar on top is looking like not only the easiest, but also the best idea for winter emergency stores??

  • Just reading the article about HMF, and its possible assistance in producing an increase in bee mortality. Obviously simply adding hydrogen gas would allow the process to reverse, but in a hive with capped honey it would not. And the bees wouldn’t like the hydrogen much anyway.

    What is it about the HMF that harms the bees? And more importantly what about human consumption? Have any tests been conducted to see if “old” honey or other sugars containing HMF may harm humans.

    I recall storyies of stored honey being eaten after many years.

    And keep up the good work with the web site.

  • I understand the winter implications, and have seen a number of recipes with unheated sugar. What does this mean for 1:1 or 2:1 syrup in the spring or fall? Does using heated water increase the occurrence of HMF?


    • Erik,

      Heating the water increases the formation of HMF, so the question is how much. It seems that HMF poses some amount of harm to colonies, but the amount varies. I can make 1:1 syrup easily without heating the water, 2:1 is trickier. So I think it comes down to asking if the benefit of 2:1 syrup it greater than the detriment of increased HMF? This year I fed 1.5:1 syrup in the fall (unheated) followed by no-cook candy boards. Personally, I want to get away from heating any bee food, but I realize this could create other problems.

  • According to Herbert G. Baker (https://hal.archives-ouvertes.fr/file/index/docid/890439/filename/hal-00890439.pdf), the pH value of nectars varied from 4.2 to 8.5.
    If you look at “How It’s made Sugar” (https://www.youtube.com/watch?v=0QRmJQoI-xU) at about 3:01, it mentioned that lime is added. And that makes table sugar to about neutral (7). But Boca in UK beekeeping forum said it good (http://www.beekeepingforum.co.uk/showthread.php?t=14964):

    “I know that there is no need to invert the sugar before fed to the bees. Actually it makes things worse.

    What I’m interested in is not the inverting of sugar with acid, but make the inversion easier to the bees in autumn when they have to do it as quickly as possible. According to my calculations the pH of 0.00001 M of citric acid is 4.7, ideal to do the job. That means about 0.2 g citric acid in 10 litres of sugar syrup. Lemon juice contains about 5 g citric acid in 100mL.

    Therefore, theoretically 5 ml lemon juice in 10 L syrup makes the optimal pH for inverting the sugar. That is so little, I think, that it would hardly change the taste. Usually juices of a plant are slightly acidic, probably the nectar too.”

  • Very difficult positions to understand. I add ACV to my cooked fondant (240°F) to increase acidity and to make invert sugar syrup. My 2:1 syrup I heat only until sugar is dissolved and add a little ACV. My 1:1 syrup gets a little ACV as well.
    So does this mean no more cooking and no more ACV?

    I don’t want to harm my hard working girls.

    • Hi Debie,

      It’s a complicated subject. The conventional wisdom is to heat sugar to make fondant or heat the water to make syrup. And people have been inverting the syrup with acid for years. I did too. But we keep learning more and more, and now we know that increases in HMF (caused by inverting with acid and heating) increases bee mortality. In many cases, we lose hardly enough bees to notice, which is why for so long we didn’t think it was an issue.

      And maybe it wasn’t an issue in the past. If you lost a certain percentage of your bees overwinter, the colony probably did okay anyway. But now there are so many other problems, including modern insecticides, poor forage, habitat loss, climate changes, and new pathogens that we may be seeing additive problems. So if you lose a small percentage to HMF, and another small percentage to Nosema, and another to mites, and another to bad weather, you soon have a colony at the breaking point.

      My feeling is that if there is anything I personally can change, I will. So even though I don’t know how many bees I may have lost to heating and inverting sugar, I am not going to do it anymore. You or others may feel differently. I offer up the discussion so beekeepers are aware of the issue, but how (or if) they change is up to them.

      And we still don’t have all the facts. New information comes to light almost every day, and we have to evaluate each piece as it comes along.

  • Rusty, perhaps a good alternative is Dr. Dale Hill’s (University of Montana) no-cook Crabby Patties recipe. He fills ziploc bags with the mixture below, puts in two lengths of 1″ x 1″ wood (to prevent the bag collapsing on the bees as they consume the pattie mixture), cuts a slit in the bag and puts the filled bag cut side down on the top bars…a bag is there all winter and replaced as needed until the first nectar flows:
    3 lb. sucrose (white table sugar)
    1.5 lb. protein supplement
    Corn syrup to make batch sticky and just holding together.

    • Janet,

      I can’t remember, but did Dr. Hill ever say why he called them “crabby?” Was that a nod to Peanuts?

      My only objection to his system is that some bee researchers (and I will have to check my notes because I don’t remember who wrote it or where I read it) believe that by mixing protein supplement with the sugar, bees are more-or-less forced to eat the protein, even when all they need is the sugar. This is most likely a problem in late fall and early winter when brood rearing is low and so the requirement for a full battery of amino acids is also low. Some of these folks felt that unnecessary consumption of protein could cause gastrointestinal distress (i.e. honey bee dysentery) if given too early in very cold climates where cleansing flights were rare. When you think about, an overwintering bee normally makes a choice whether to eat protein or carbohydrates (or both) because they are stored in different cells.

      The answer to this was to provide the protein separately from the sugar (as a protein patty embedded in the sugar) so the bee could make a decision. This “free choice” feeding is used with many animals, such as free choice feeding of oyster shells to poultry, or the free choice feeding of mineral salts to rabbits.

      I have evolved from mixing them together to feeding them separately, and this year I had excellent success with a pollen patty embedded in a no-cook candy board. All of my hives polished off the sugar, about a third ate the entire patty, and the other two thirds each ate a portion of the patty, but left the rest. It was interesting to note the pollen patties did not dry out and were still nice and moist by spring. I attribute this to mixing the pollen sub with sugar. I believe the sugar absorbed water from the hive, keeping the patty moist.

      Of course the need for year-round protein will vary with the amount of winter brood rearing, which will vary with local climate. But for here, I will definitely use the no-cook candy board with embedded free-choice pollen patty again this winter.

  • The name comes from the original chef’s grandson, and is correctly Krabby Patties, as junior was a SpongeBob fan! Dr. Hill does advise using a much lower protein content for fall/winter, only switching to the full protein in January, when HRH should be laying well again, and certainly here on the coast we get lots of flight days, which should prevent the dysentery issue. And here, I see the bees haulin’ pollen all of our wet and rainy winter. Note that these patties are used in full on Eastern winters, and no one mentioned any issues with dysentery. That said, it would not hurt to provide a choice in the bag of Krabby Pattie mix both with and without the protein supplement…it would be easy to fill the bag 2/3 without and 1/3 with.

    I have always made fondant, which is as you say, not a fun task (messy, time consuming, and opens up the possibility of boiling sugar burns), and involves possible issues with creating an unhealthy food for the bees. I will be Krabby Pattie-ing this year.

    Original recipe here: https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiR-_3xj7fNAhUP4GMKHR59DJ8QFggdMAA&url=http%3A%2F%2Fwww.lincolnlandbeekeepers.com%2Fuploads%2F1%2F0%2F6%2F4%2F10649295%2Fkrabby_patty_recipe_v1.pdf&usg=AFQjCNFlnbaM4X4BC3SUJByoJiYlmW03_Q&cad=rja

  • Me too. Offering choice is a more prudent approach. But I will ask Dr. Hill about the ramifications of mixing the protein supplement in. I also saw on one site the beekeeper fed the KP’s by cutting off the ends of the ziplock bag, allowing the bees to nibble inward from the edges.

  • Hello folks. I’m used to produce syrup simply mixing sugar to tap water. No heating at all. I can dissolve up to 35Kg of granulated sugar in 20Kg of water. First I fill the “mixer” (an inox 100L can with bottom drain valve) with water. Than I pour 15kg sugar. I use a battery screwdriver to mix about 10 minutes reversing any minute. Than I leave it settle about 1 hour before adding 10Kg of sugar and stirring other 10 minutes and another hour to settle and finally other 10Kg of sugar and 2L vinegar. Last addition seems a little bit more difficult as sugar granules seems to float and pack but after 10 minutes I leave it overnight. Following morning you can find little amount of sugar in the bottom of the can. Now you can divide into smaller tanks and distribute to hives.

  • Rusty, I’m planning to feed my hives sugar for the first time this year and have a quick question about the no-cook sugar cake recipe related to vinegar and HMF. Your recipe (and most others I’ve seen) includes a small amount of vinegar, which I understand from one of your excellent posts is to prevent mold from forming on the cakes. In a presentation to the UK National Honey Show a couple of years ago (https://www.youtube.com/watch?v=R86DOPiX-3s), Ann Harman mentioned that invert sugar is not recommended for winter feeding because when it is made from sucrose with acid, HMF is formed. Since vinegar is mostly acetic acid, should I be worried about the potential for HMF, or more worried about the potential for mold? I am planning to add a small amount of Honey B Healthy to my sugar cakes and am wondering if this might retard the mold enough to allow elimination of the vinegar. What do you do think? Thanks, and keep up the GREAT work!

    • John,

      Great question and it just so happens I’ve been working on a post specifically detailing this issue. If you read this post however, the second section called “Honey bees do it with invertase” explains how the addition of an acid increases HMF production.

      I have stopped adding vinegar to any sugar preparation just as I have stopped cooking any sugar preparation because of the HMF. This is a case of me needing to update my old posts. I’ve been writing this blog for seven years, and as I’ve learned and studied more and more, many of my practices have evolved. So I will put this one on my (rather long) list.

      HBH is fine and the bees love it. I don’t worry about mold much. Mold won’t hurt the bees the way HMF can. When colonies are short of food, I have trouble keeping them stocked with sugar anyway, so in my experience, mold doesn’t stand a chance. If it starts for some reason, you can wipe it off. Like I said, it doesn’t hurt the bees and we shouldn’t apply our standards of palatability to them.

  • Regarding your point about updating your old posts… not sure if it’s possible, but it would help if the date of the post were at the top and larger. In fact, it would be great if the row with the date and links to related articles were at the top instead of the bottom. And possibly have an index by date? (Aging content is such a daunting problem all over the internet!)

    Regarding “the inverted product becomes acidic because the fructose donates a proton during the reaction and thus behaves like an acid”… is the HMF formed at this point? If this reaction happens in the honey stomach, why does HMF not form in their stomach?

    This is an interesting article about feeding. It also mentions sterilizing the jars between feeding – I didn’t realize that was necessary! http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0018/532260/Feeding-sugar-to-honey-bees.pdf

    Your articles (and beekeeping in general) are so insanely interesting! I’m completely obsessed with it and love reading your articles!

    • Kim,

      Well, I might be able to make the date larger, but I can’t move it to the top without changing themes. I want to change it someday, but for now I would be happy if I could get my ssl (encryption) to work properly. “Index by date” is an interesting idea. I’ll have to mull it over.

      I need to get a pencil and piece of paper to see if I can answer the HMF question. Offhand, I don’t know. The nectar in the honey stomach doesn’t go down to the digesting stomach, which would keep the bees from absorbing it. On the other hand, it seems it would get stored in the honeycomb and the bees would eventually consume it.

      The only time I sterilize feeder jars is when they get moldy. I will have to read the article.

      Your comment is going to keep me busy…

  • I think I have screwed up making fondant. I ended up with something between fondant and hard candy. It’s a very thick, viscous caramel consistency. My other concern is that it is dark, so I’m wondering if I created an HMF issue and now cannot use what I made to feed the bees.

    For a base, I started by using some leftover 1:1 sugar syrup that I had leftover. This also had Honey-B-Healthy in it, as well.

    So, I used the leftover syrup and added more sugar, then heated the whole thing up. Using a candy thermometer, the temp got up to about 250 degrees, then I backed it down and cooked it around 180-200 where it simmered for a while to reduce. I then let it cool down for a bit and pour it into some molds and put it in the fridge overnight.

    So…do you think I can use this to feed the bees or do I have an HMF issue? Did I just create a mess that needs to be thrown out?

    • Mark,

      I worry about the dark color. Once sugar caramelizes, it’s not good bee feed. And the HMF isn’t good either. Starting about four years ago, I stopped heating sugar altogether. Now I use no-cook sugar or syrup.

    • Rusty,

      I have a neighbor beekeeper who has some 42/43 corn syrup. He says that’s what he feeds his bees with…but my understanding here is sugar only as corn syrup has GMOs in it.

      • Sugar can be GMO also, especially beet sugar, although I hear that cane sugar can be GMO as well. In any case, research has repeatedly shown that honey bees are unaffected by GMO syrup and sugar.

  • Rusty, at what temperature does HMF start to become toxic to bees. I’ve been searching for sugar brick recipes and most call for baking at 200F for 15min to 1 hr!?

    • Javier,

      HMF can be toxic to bees at any temperature. I think what you were trying to ask is at what temperature does HMF begin to form. The answer is complex. It will form in the mid-80s F after long-term storage, but it can form much more quickly at high temperatures. The higher the temperature, the faster it forms. Sugar bricks can be air-dried at room temperature, a much safer alternative. Mine take 3-4 days to dry, depending on the humidity.

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