Raise your hand if you’ve ever plumbed the depths of your fridge for maple syrup, poured it onto hot pancakes and out plopped a fuzzy mold. (Author sheepishly raises his hand.)
Let’s just say it wasn’t the topping I’d hoped for.
But what gives? Does maple syrup go bad? How long does maple syrup actually last?
In this article we’ll answer these questions at length. If you want practical solutions, skip the next three sections. All you lab goggle types, follow me.
First, Let’s Define Terms
What do we mean when we say maple syrup has gone bad? We should distinguish between stale and spoiled. Nuts can go stale; so can bread. Stale food is safe but has gone dry or lost its flavor. Spoiled, on the other hand means, it’s unfit for consumption.
You may be surprised, but maple syrup doesn’t get stale. Maple syrup doesn’t expire. If made to modern standards and properly graded, its flavor will not change perceptibly for years and years.
However, maple syrup can be spoiled, or “go bad.” This change happens due to contamination of one kind or another, non-living or living.
Non-living contamination would include minerals, wood chips, dust or ash. But these are filtered out in any self-respecting sugarhouse (a fun term for a maple syrup operation).
Living contamination, on the other hand, can develop over time in an opened bottle. Most of these living creatures love moisture, sunlight and warmth. They float in from the air. They include bacteria, yeast or mold. From here on out we’ll refer to these collectively as microbes.
Caveat: In this article, we’re talking pure maple syrup, as opposed to imitations, often called “table syrup.” Here’s how to spot the difference. The stuff pretty much never goes bad (go figure).
Sugar as a Preservative
For starters, maple syrup resists microbes because it’s so sweet. I know that’s counter-intuitive — don’t those tiny buggers love sugar? Let’s break that down.
Sugar has long been used as a preservative. In fact, ancient Greeks lovingly mixed quince with honey and packed it tightly into jars that could keep for a long time in a cellar.
To distill the dense science, microbes need water more than they love sugar. And sugar is soluble, in essence binding up the water molecules. When syrup is boiled, concentrating its sugars, its water content is essentially unavailable to microbes. That is, as long as it’s tightly packed and sealed.
In an opened bottle of maple syrup, its sugar content works against it, attracting moisture from the air, which ends up pooling on the surface, once again available to microbes. That’s why syrup is packed tight and why you should close it tight (more on storage later).
Food Safety in the Syrup Making Process
To dive deeper, let’s recap how maple syrup is made in terms of food safety.
Watery maple sap, sterile within the tree, flows out through plastic piping into holding tanks, both of which are sanitized after every sugaring season. Then sugarmakers (as they’re called) boil the sap until it thickens into the syrup we lick from our fingers.
According to Arnold Coombs of Bascom Maple Farms, the syrup reaches 219° F (sugar raises water’s boiling point), and the heat further sanitizes it. Often resting in holding tanks before bottling, it’s then filtered and heated again to a minimum of 180°, a temperature that sanitizes the container as it’s poured in.
How Long Does Maple Syrup Last?
So we’ve covered whether maple syrup expires. But how long is syrup good for? How long does syrup retain its flavor? Unopened— it’s good indefinitely. Opened — it will last a year if you refrigerate it, and years if stored in the freezer.
How to Store Maple Syrup
Most maple syrup comes in a glass bottle; ours certainly does! Most plastic containers are slightly porous, allowing air to get through, thus making syrup more prone to contamination. Tin certainly has a farmhouse allure, but some say it can give off a metallic taste over time. Not only is it classy, glass recycles well and can be held up to the light to check for spoilage.
Because most microbes need warmth, sunlight and air flow, storing unopened syrup in a cool, dark and enclosed space will reduce the chance of contamination. Think cellar or dark pantry, just not over the oven. Once opened, you should just refrigerate it. Your refrigerator will dissuade microbial growth for the same reasons.
You can also stick maple syrup in the freezer to prolong its shelf life for years. In the freezer, the syrup will thicken but won’t freeze. Why doesn’t it freeze? Because maple syrup has an incredibly high sugar content.
How to Tell if Your Maple Syrup Has Spoiled
At the risk of stating the obvious, the first thing you should do is check the best-by date printed on the container. Now, that’s just a loose indication. You should still use your senses. Maple syrup could still be spoiled before this date and safe after this date.
The most common microbe to spoil maple syrup is mold. Found floating on top, this mold is in the kingdom of fungus (for you taxonomy nerds out there). While you may think of mold as one organism, there are thousands of types and species.
Most mold found in maple syrup belongs to a class called wallemiomycetes. While the vast majority of molds require water-rich environments, these are a super hardy bunch. Though the consensus is unclear whether they are dangerous, who would want to try?
Just throw it out. If you’ve stored it properly in the refrigerator or freezer, the chances of losing your liquid gold to some floating yuck is slim.
Off Flavors, Haze and Crystals
If there are off flavors, it’s due to mishaps in the maple syrup process. Use your nose. These scents can range from peanut butter, popcorn, even cardboard flavors, according to The Maple News. Demand better.
If you notice your syrup’s hazy or has light sediment on the bottom, that’s simply because it may not have been filtered.
This trait is more likely coming from your uncle’s operation than a proper sugar farm, but it’s nothing to worry about.
The sediments are minerals that occur naturally in sap.
If your syrup is crystalizing, it’s because additional water may have evaporated, concentrating the sugar so much that there’s more than can be dissolved.
Coombs warned, “Every time someone microwaves their bottle and puts it back in the fridge, they’re evaporating a small amount of moisture, so it will get thicker and eventually crystallize at the bottom.”
So if you want hot syrup all over your pancakes, simply heat up a small portion.
But crystals are just sugar, so simply scrape them away from the bottleneck if you can. If you can’t, add a drop of water to the syrup and set it in a bath of simmering water to re-dissolve those sugar crystals.
Just don’t bring it to a boil, further supersaturating the sugars—unless you want something resembling hard maple candy. We wouldn’t blame you!
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