Reader Question: Off Flavor in Maple Syrup

by Tig Tillinghast

Another reader question:

I am looking for some help in my own attempt at maple sugaring. This is the first time we have ever attempted this, and the syrup we produced has a very off flavor. Almost like rotten fruit? Any tips? -Tara

There are a few things that can cause these off flavors in maple syrup. I’ll list them out, and perhaps one or two will jump out at you.

Perhaps the most common cause of such an off flavor is boiling sap that has been kept too long before boiling, or stored in a warm and/or concentrated form. I made some very nice rotten fruit maple syrup a year ago on my last day, concentrating some sap partially and then letting it sit up in the sugarhouse attic for three days getting nice and toasty in the April sun before doing my last boil. Specifically, it tasted like rotten oranges. I sacrificed that batch to the farmyard as an offering for a good maple syrup season in 2009.

Remember that while bacteria are breeding in your sap, they’re eating your sugar and excreting compounds that are generally not good for the maple syrup flavor. The specific type of critters you have growing can vary, and their off-flavors will vary along with them. We’re contemplating installing an ultra-violet filtering system on our sap and concentrate tanks next year, so as to be able to more comfortably store sap and boil more strategically. For the backyard sugarer, that wouldn’t make any sense at all. You might, though, contemplate whether or not you really want to hold over sap from Monday’s buckets to the Saturday during which you have time to boil.

Sometimes, rather unpredictably, maple trees will go through a “metabolism” stage, where it will generate an off-flavored sap. When that happens, it’s usually not a local phenomenon, and can be seen across an area. I haven’t had this happen to me, but a few years back a lot of New England maple syrup producers found this happening, and they reported that the maple syrup had a distinct “sweaty sock” taste. Makes your mouth water just thinking about it. Proctor Maple Research Center is in the midst of some good research on this phenomenon. They’re trying to pin down both the cause and any actions a sugarmaker might take in order to prevent or correct the problem.

I have a few local folks who just started maple syruping coming by the sugar shack this year, showing off some samples of Fancy maple syrup. That’s impressive, given that it’s tough to make fancy off a stovetop, but it’s also fairly common for the light and subtle taste of fancy maple syrup to reveal the presence of pan cleaner residue, or even of odors baked into the sap while boiling, such as cigarette smoke or just plain not-very-well-vented firebox smoke. With the sometimes fruity taste of fancy maple syrup, those off-flavors can combine to give a rotten fruit sort of flavor.

Finally, we’ve seen different sorts of areas in New England throw different maple syrup flavors. Our bush behind our house, for instance, throws a vanilla-like maple syrup flavor. The bush we rent over in Strafford, the town next door, has an intense “put-hair-on-your-chest” maple maple syrup flavor. This past year, my wife held a maple syrup tasting with author Amy Trubek, the author of “Taste of Place.” We had a couple dozen folks in Norwich tasting maple syrup from different regions, and it was quite stark how they had different flavors, ranging from the woody to the fruity. You may find that you have trees that throw a particular flavor. If it really tastes like rotten fruit, it is likely that boiling the sap more quickly, keeping it cool when not boiling and finishing the syrup to a good thickness will make the flavor seem a benefit rather than a problem. Please do let us know if any of this sounds relevant, and if you find your maple syrup is able to shed the off flavor.