The fungus in my maple syrup
Last week an uninvited guest showed up for breakfast. As I poured maple syrup over my son’s waffle, Plop! A perfect dime-sized fungus colony spilled out to crown that waffle like a malevolent pat of butter. The maple syrup had been sitting out, unrefrigerated for, um, quite a while.
A 10 cm custard cup of maple syrup, with guest (click for a closer look)
What would you do? I asked my 4-year-old whether he could touch his nose with his tongue, and used mommy stealth to swiftly replace the contaminated waffle with a new one (with honey on it). Crisis averted. Finally, and I’m sure you would’ve done the same, I packed up the offending maple syrup for a rendezvous with my microscope. Sometimes uninvited guests turn out to be pretty darned interesting, if you take the trouble to get to know them.
A fungus that can grow in maple syrup is not your average everyday mold, it’s a xerophile. Xerophiles grow in places that are too dry and hostile for your average fungus. OK, maple syrup is wet, but it’s also extremely high in sugar. All that sugar has the effect of pulling water out of cells, and the vast majority of fungi can’t grow in maple syrup at all. No matter how much they might like it in smaller quantities–the water in maple syrup isn’t “available” to them.
Water activity (aw) is a measure of “available water.” Water itself has an aw of 1.0 (all the water in water is available!); for dried milk powder aw=0.2 (hardly any water is available). To protect food from spoilage by molds and bacteria without refrigeration, you want to reduce water activity below 0.8. You can do that by drying out the food, or brining it with either a high salt or a high sugar treatment. According to this site, maple syrup typically has a water activity of about 0.87 to 0.88, pretty hostile to most molds. Only a few xerophiles can live in it,1 including our surprise guest, Wallemia sebi.
What a handsome fungus! Wallemia sebi is a xerophilic mold that specializes in growing on things of low water activity, like dried fruits and jams, and salted meats and nuts. It grows in salterns (the evaporating beds in which sea salt is produced), and its bumpy little spores are found fairly often in indoor air.
A nice study by Zalar and colleagues2 reveals that Wallemia is a distinctly weird mold. It’s so weird, and so distantly related to most other molds, the authors erected a whole new class of fungi just for it, class Wallemiomycetes. Within this entire class there are only three species, Wallemia sebi, W. muriae, and W. ichthyophaga. Just for reference, you and I and my dog and almost every furry creature in the world are Mammals–that’s a class too.
The Wallemiomycetes are distantly related to the usual xerophilic suspects, Aspergillus and Penicillium. In fact, they’re distantly related to just about every other fungus we know. Zalar et al. found that they’re out there by themselves on a very long evolutionary branch. They emerged very early, just as the major basidiomycete groups were evolving. It’s hard to imagine Wallemia as a basidiomycete, because it has never been seen make a sexual fruiting body, and that’s how most basidiomycetes are classified. Mysterious and beautiful, that’s Wallemia.
A lot of people think that a mold is a mold is a mold, but that’s just not so. The mold that’s rotting your lemon is not the same one that’s growing in your maple syrup, or eating your strawberries. In fact, your lemon, maple, and strawberry molds each belong to a different phylum of fungi. Proust said it:
The real voyage of discovery consists not in seeking new landscapes but in having new eyes.
- To avoid moldy maple syrup, producers heat-sterilize it before selling it to you. Once you open the bottle, the fridge is your friend. The fridge doesn’t change the aw, but the low temperatures in there slow or stop the growth of most fungi. By the way, fake maple syrup resists molds through the miracle of chemical preservatives (usually sodium benzoate and sorbic acid). You don’t use fake maple syrup, do you?
- Zalar, P., G.S. de Hoog, H.-J. Shroers, J.M. Frank, N. Gunde-Cimerman. 2005. Taxonomy and phylogeny of the xerophilic genus Wallemia (Wallemiomycetes and Wallemiales, cl. et ord. nov.) Antonie van Leeuwenhoek 87: 311-328.
- ERRATUM: When I first wrote the article, I overlooked an important new publication on Wallemia (thanks, Else). It sheds a little more light on Wallemia’s relationships, and includes a thorough discussion of Wallemia’s strange characteristics. Here’s the citation: PB Matheny, JA Gossmann, P Zalar, TKA Kumar, and DS Hibbett. 2006. Resolving the phylogenetic position of the Wallemiomycetes: an enigmatic major lineage of Basidiomycota. Can. J. Bot. 84: 1794-1805.
Thanks to Kent Loeffler, who took the photos of Wallemia growing in little 10 cm custard cups full of maple syrup.
Great job of making xerophilic mold an interesting and timely subject. Bravo!
came here on sitta’s recommendation. Nice post, especially the medium-range closeup that makes the fungi look like limpets or barnacles. I’d like to know where the other two species of Wallemia are found – other maples? other tree saps? someplace totally different? Is Wallemia a maple-syrup specialist or is that just one of its tricks? Good explanations always breed more questions, so thanks for writing, and keep up the good work.
Hi sitta and Hugh, welcome to the fungosphere.
Hugh, it took Zalar et al.’s molecular phylogenetic work to figure out that there are three Wallemia species. We’ve only had a couple of years to learn about which species likes to live where, so I can’t answer your question with any authority. According to Zalar et al., W. ichthyophora is known from salterns, salted meat, and fish. It can grow on sugary media in the lab, so the odds are good that it occurs on sugary things out there in the real world, too. W. sebi and W. muriae are known from the same kinds of places, plus all kinds of dried sugary fruits, jams, and syrups, salty foods, plus indoor environments. Wallemia sebi is not a maple specialist, it’s a generalist xerophile. It can also grow on dried hay. Look out! When inhaled in quanitity, the powdery little spores of Wallemia spp. can cause Farmer’s Lung Disease (hypersensitivity pneumonia–the spores cause an inflammatory response in your lungs without actually growing in there).
Hi Kathie,
How exciting to get Wallemia on the maple syrup!
Brandon Matheny et al. just published on this group, in Can. J. Bot. 84: 1794-1805. 2006, and figured out where these enigmatic fungi belong (more or less, as there was conflicting evidence from different DNA regions they looked at).
else
Thank you for the comment, Else, I’m very sorry I missed that nice paper!
Matheny et al. used a multigene approach to investigate exactly where Wallemia belongs among the basidiomycetes. Even with data from six genes, the results aren’t entirely clear. It’s safe to say that the Wallemiomycetes are an old group that diverged early among basidiomycetes, and that they’re weird in several wonderful ways (Are they having sex or not? Do they have a parenthosome? Are they related to those odd root-smut-thingamabobs?). Do have a look at Matheny et al.’s recent paper for a thorough discussion, everybody.
Thanks all
Here is great useful information about mushroom
[…] Welcome to Supermarket Mycology, an irregular series of posts on fungi you might well encounter in your everyday life. We’ve already kicked things off handsomely with time lapses of rotting strawberries and lemons, and of course there was the cautionary tale of the moldy maple syrup. Fungi are more ubiquitous than most people imagine; supermarkets house a surprising number of both good (tasty or useful) and bad (unwanted or ugly) fungi. […]
Questions:
Is this the likely mold found floating in maple syrup?
Is it toxic? (Or, can one fish out the floating mold and eat the syrup?)
Dear Maple Syrup Maven,
Wallemia is ONE of the molds that might be found floating in maple syrup. Other xerophiles might be found there as well.
Whether to throw out the syrup is a hard question to answer. How much mold is there? Does this fungus make toxins in that sugary environment? Are those toxins produced in enough quantity to hurt you? Isn’t it frustrating that I don’t know the answers? I generally tell people not to eat moldy food. At least with a solid food (like cheese?) you could theoretically cut around the mold and remove it (but cut deeply, because the mold extends further in than you might think!). In a liquid, any emitted toxins can diffuse right in, so removing the colony may not remove the toxins. I personally threw out my moldy syrup without further toxicological analysis… but not without some sadness.
My son has unknowingly eaten maple syrup mold that he fixed in some BBQ sauce. (His own personal concoction). Anyway, he now has a horrible head cold and lots of “snizz” in his sinuses. Could it be caused by the maple mold??
Gosh Lisa, I have no idea whether a fungus in maple syrup would be connected to your son’s “snizz.” I’d bring it up with your doctor.
Actually, what I’ve been doing for a couple decades now is fishing out the floating mold, reheating the syrup to temp and then refrigerating. No “snizzes” yet!
Yes, we make maple syrup, and what we do and tell people who buy our syrup to do, is fish out the mold (a fork usually works well) and then reheat it the syrup to a boil. You don’t need to let it boil and in fact this will create sugar sand as the minerals in the syrup tend to precipitate around 200*, not bad for you but gritty. Loved seeing the pictures of the mold closeup! Too cool. Interestingly we find that if you use the syrup jar often and leave it out mold doesn’t seem to have a chance to make a foothold.
Hi. I have uncovered a fungi which has a morphology that defies the very definition of fungi. It may be a result of rDNA experimentation in the development of e-coli plasmid host antibiotics manufacturing technologies. I have photo’s and sample evidence. The product is subject to crystallization. I will e-mail you photo’s if interested. Greg Beals
Hi,
I stumbled on your wonderful blog, it’s great! Serious question, I came down an hour ago to our kitchen and without even looking over the Sunday paper, poured green fungi filled maple syrup from the fridge on the my pancake and put another on top and took a big bite of it! Tasted funny and acid and I looked and saw the inner pancake was green with fungus! So was the inside of (real/organic) syrup bottle! Only half kidding, I’ll be ok, right? It was gray/green fungus, Wallemia sebi? Thanks for the promptest response you can give! George
Well George, I doubt that your gray-green mold is the same as my salmony-pink Wallemia. Perhaps your maple syrup was sprouting a species of Penicillium? Those are often greenish, and many Penicillium species are xerophiles (can grow in sugary places–see above). As to whether you’ll be OK, my bet is YES. But don’t eat any more of it–although some Penicillium species make friendly things like antibiotics and blue cheese, others make powerful mycotoxins like penitrems and mycophenolic acid. And by the way, I strongly disagree that filtering out, heating up, or skimming off the mold will address the problem. Throw that maple syrup away.
UPDATE: George let me know that he survived his moldy pancake experience without detectable ill effects. For the benefit of science, he wants us all to know that “the taste of it was kind of an effervescent-vinegary type of sourness.”
Thanks George for your input, I just had some wonderful maple syrup from Canada on my sweet patotoe fries. As I was putting things away I noticed the mold in the bottle, YUK! I didn’t have any mold that I know of, but it makes my throat feel odd just to think about it. In times past I would have reheated it and used it, but after reading the material posted I am going to throw it out. Thank you people for your posts.
In my family’s house a mold once grew in a bottle of Chinese oyster sauce that had been opened and left capped but unrefrigerated. Oyster sauce is extremely salty, the Asian version of A1 steak sauce. The mold apparently could tolerate it, but is lost to science as we threw away the entire bottle in disgust.
the fungi that came out of my plastic maple syrup bottle today is brown and powdery looking.It looked to me like cinnamon or cocoa powder spilled on the maple syrup. When it mixes with the syrup it looks similar to the brown dirty staff that come on surface when you are boiling meat or chicken.i poured it into a glass.they are mostly on the surface and some on the sides attached to the glass surface.But i think there are/might be very small particles all over.I ate my waffle although tried to avoid the parts with mold but i will throw the rest away.I wish i knew if this was a harmful, beneficial or neutral species..
Well done Kathie………….nice article
my family and I ate pancakes soaked in Maple syrup growing a beige fungus without realizing it. Tasted slightly nutty/musty, almost like truffle. No side effects.
Fungus looks like delicate leaves that have been left in a liquid and have become limp. Brownish beige (not green). Was growing in a gallon jug of Canadian maple syrup (pure syrup).
Never had this happen before when we were buying it in steel jug even when it was not refrigerated.
There’s more moldy syrup out there than I suspected! I’ve had a lot of response to this post, both on and offline. Must have touched a nerve.
Anees, I doubt whether plastic vs. metal has much impact on moldiness. I think there are two more important factors: 1) the right kind of spore (of a xerophilic fungus) has to fall in at some point; and 2) the water activity has to be high enough to permit growth. The water activity of syrup varies among batches, but your syrup might also get more watery if you leave the top off, or pour a pitcher-full of warmed syrup back in after brunch.
I don’t like molds in my food any more than the next gal, but I admit I’m sometimes excited to find them, especially when they’re as cool as Wallemia sebi.
I’m fascinated to read about the varieties of mold that can grow on maple syrup! Thus far, being a cheap-skate, I’ve just poured the syrup through a fine sieve, but I confess that the syrup is tasting a bit acidic, so I suspect that the mold (a beige one) must be causing the syrup to ferment, even though the mold’s only visible on the surface…Perhaps a mycologist could comment on the ability of a mold to ferment something as viscous as maple syrup???
Hi Marcia, mold might be only visible on the surface, but, well, I have two things to say. One is that there might be little strands of mold floating invisibly around in there. The other is that molds eat their food by secreting enzymes and other metabolites right into it. So the maple syrup has surely been somewhat modified (fermented? tainted?) by that surface mold. I doubt the viscosity of the syrup would daunt a determined mold. Not sure about the oxygen content at the bottom of the syrup though–lack of oxygen could slow a mold down.
I have had the same thing happen to me, but never thought to save the offending syrup for analysis. Very interesting and entertaining. I will be borrowing the tongue to nose distraction for future use on my daughter too.
I too poured syrup on my waffles today and it came out in a sudden wave, spilling everywhere. As I cleaned it up the syrup I tasted some and it which seemed normal. I then discovered a skin of gray-green mold in the container that apparently broke loose and caused the wave of syrup to cut loose on my food. Of course I had reason for alarm, but after reading these posts I assume I will be okay from tasting it and I won’t be ill? I know botulism is a really nasty one…
Hi, it’s me, Kathie, fungus chick. It’s true that several have posted here after surviving a dose of maple syrup mold. It’s true that we often eat molds without noticing them, with little ill effect. But it’s also true that the molds that are common syrup contaminants can make toxins. My firm advice would be to throw it out. THROW IT OUT, FOLKS!
[…] To give you a feel for the site, here is an excerpt from a post titled the fungus in my maple syrup: […]
I too found mold in my plastic jug of maple syrup. The mold was mostly golden yellow and beige in color. Searching for the safety of using maple syrup after removing the mold and proper storage, I found this site and maple syrup producers’ sites. According to some, the syrup is safe to use after removing the mold and reheating the syrup. They called this mold a FALSUR MOLD. Is this a real mold variety? Mushrooms are fungi and some are safe to eat so is it ever safe to eat mold or fungi?
Peety, I don’t know what mold you have, and I have never heard of a mold called Falsur mold. I don’t have a definitive answer on whether it is safe to just reheat and strain your syrup. As I’ve discussed above, straining out mold does not remove enzymes and toxins it released into the syrup. So my recommendation is to throw it out.
To answer your other question: Yes, it is safe to eat some fungi, and some others will kill you or make you quite ill. The trick is to know which is which! If you asked the same question about plants I would give the same answer.
My family experienced the first syrup slime this morning. waffles with strawberries, blueberries, powdered sugar and vermont maple sugar. Luckily I noticed the slime when I poured the syrup from the container into a pitcher for warming. I fished off the slime, boiled the syrup and watched silently my family enjoy their breakfast. I threw the leftovers away. I think we will all be fine but will let you know if anything happends to us. Thanks for all the information of this subject.
Kathie….With the 1st snow of the winter, I was pouring maple syrup (always refrigerated after use) over my wonderful, hot-off-the-waffle-iron banana oatmeal waffles. I’ve always thought that high sugar content meant that molds/bacteria absolutely couldn’t grow, so I refused to acknowledge that the maple syrup could possibly be the origin for that moldy flavor. When I finally had to admit that’s the source & poured the syrup into a glass pitcher, I saw the delicate molds suspended throughout. The silver lining is that I found the info I wanted tucked in the comments to a wonderful piece about tracking down your xenophile (& overturned my long-held, but oh-so-wrong beliefs). Thanks for such an interesting Sunday morning…& now I promise not to blithely tell folks to go ahead & use that moldy syrup.
HI everybody! To all of you who are reticent about throwing out maple syrup contaminated with mold, let me tell you my very recent experience; in fact, so recent, I could be quite vivid in the recollection of last weekend, but for your sakes I’ll not go into detail! Let me just say that till now I was simply straining the precious syrup to remove unwanted guests that showed up to partake of my heavenly delight. But it seems this time a more vehement sort took revenge!! Sunday, I enjoyed my syrup on pancakes with no disagrable taste, but less than an hour later I found myself slumped onto my sofa, feeling queazy and feverish. After a few unbearable minutes, thinking about what was happening to me, wondering what to do, I decided to eject the culprit. I stumbled across the living room and made my way to the toilet, tickled the back of my throat and… I’ll spare you and keep this rated G. Needless to say, I IMMEDIATELY felt so much better. I guess I’ll never eat anymore moldy syrup. The event wasn’t worth the savings! There are toxins in there!!! Beware…
I never knew about the differences of mold, quite fascinating really. I enjoy the high-powered closeup pictures also, never seen anything like it.
Yesterday at our church pancake breakfast we found 10 or our 20 bottles of syrup not only had a thin coat of mold on top of the syrup it also had a very strong potent smell. With the smell we didn’t have to wonder if we should just dump all the syrup. The only thing that had changed with its storage was that with the extremely cold weather outside we think the heat may have been on in the closet more then usual.
To toss or not to toss?
After reading the debate, I decided to offer up myself as a test subject. We had a grayish layer of mold floating on the top of our maple syrup. No odor. I fished it out, boiled the syrup and had a couple of table spoons. Tasted perfectly normal. No ill effects 12 hours later and counting.
Of course, I don’t know what the species of mold was, which makes all the difference. E.g., Aspergillus flavus and A. parasiticus produce heat-stable aflatoxin (chronic exposure to which which can lead to liver cancer in people infected with hep B).
I had no idea only certain types of molds could grow in syrup.. I have had some bottles in my refrigerator for a long time that I still sometimes use though and the thought of getting a ‘plop’ of mold really grosses me out.
I had my first experience with moldy maple syrup today. I served waffles and maple syrup at a brunch. Everyone loved the waffles and syrup. When I went back for seconds a dark grey-blue-green slime slithered out of the plastic bottle onto my waffles. I was shocked (since I served it). I immediately threw out the bottle and replaced it with another slimeless bottle.
Also I threw away the waffle with the slime but ate the other with non slimy syrup. It tasted great but I am definitely hoping that no one gets sick. It’s now about 7 hours since I ate the syrup and I feel fine. Keeping my fingers crossed.
I just had a little moment of horror in the kitchen when, while reheating my dinner, I looked nonchalantly at my bottle of maple syrup on the bench and something looked back!
Thank goodness for your blog, which has explained that my syrup is not, in fact, harbouring an alien life form, but has merely open it’s sticky arms to a cheeky little mold.
I thought my morning bowl of porridge and syrup had developed an unusual tang this week!
Of into the compost heat it goes…
Ok I’m convinced, so after I threw out my gallon jug of moldy maple syrup, I went to the natural food coop and bought some maple sugar! I mean real maple sugar made 100% from boiled-down maple syrup. That’s what I’m going to put on my oatmeal from now on (with half and half).
The maple sugar seems to be very dry, not at all like those wet brown sugars you see a lot of on the shelves.
I had never heard of “water activity” before reading your article. I think it’s so great that there is a way to measure such a thing, so thanks for explaining it. I poked around a little bit on the web and found out the water activity for honey is about 0.6. Guess that explains why it keeps so much better than maple syrup. Couldn’t find a number for maple sugar though. Must be pretty low. Do you have any idea what it would be?
I came online to see if my maple syrup was what made me sick. The first time I used it I just had mild stomach upset. Today I put some in my yogurt and have had severe diarhhea. I poured it into a bowl and saw dark clumpy strands. I am convinced it was the syrup. I love my syrup but will no longer buy a large quantity.
Changed viscocity! A bottle of my homemade syryp developed a little white mold on top and when I poured it out to skim it off and boil, I discoverd the syrup had nearly acquired the consistancy of jelly. Really gelatanous. Could anyone possibly tell me why this happened and what it could mean for the quality of the syrup?
Hi David, even though it looks like the mold is growing only on the top, it’s quite possible there are hyphae growing invisibly in the liquid below. This could have the effect of increasing the viscosity. Alternatively, the fungus might have been secreting polysaccharides (and who knows what else) into the syrup. Again, I strongly recommend that you discard moldy syrup.