There are a number of ways to cook maple syrup at home. Propane boilers, wood stoves, cinder block boilers or a professional maple syrup arch all work just fine. Regardless of how you boil down the syrup, you’ll arrive at the endpoint and need to can maple syrup to ensure it stores properly.
When is Maple Syrup Finished?
Maple syrup is done when it reaches 7.5 degrees F above the boiling point of water. Most people know from science class that water boils at 212 degrees F, but that’s only true at sea level. Water actually boils at different temperatures based on your elevation. For every 500 feet above sea level, water boils a degree cooler.
Our home is just about 1000 feet above sea level, meaning that water should boil at roughly 210 degrees F. We cook our syrup to 217.5 degrees, or as close as we can get.
During the final finishing process, the temperature rises rapidly and it’s hard to stop at that exact point. Depending on how even the heat is applied, there may also be places in your finishing pan that are warmer or cooler. This is a guideline, and don’t drive yourself nuts trying to hit it exactly.
Old school Vermonters don’t bother with a thermometer. My neighbor who has been sugaring for more than 50 years determines when it’s done by how the sap runs off a spoon. He showed me, and the subtle differences in texture were barely noticeable, but after 50 years he knew just what to look for. For now, I’ll stick with a thermometer, but after 5 years of sugaring, I’m getting close to being able to determine it by sight.
Filtering Maple Syrup
Once your syrup reaches 7.5 degrees above the boiling point of water, it’s finished and ready for filtering. Most producers filter their syrup through cotton or cloth filters to remove what is known as “maple sand” or extra mineral deposits within the syrup.
Personally, I love the maple sand. It settles to the bottom of the jar, and when the jar is empty, I eat the maple sand with a spoon as a special treat. It’s a bit gritty but full of maple flavor and sweetness, a bit like very soft maple candy. I tell myself that it’s a great way to get my minerals, but really it’s just downright delicious and I see no point in filtering it out.
How Long Does Maple Syrup Last
The shelf life of maple syrup depends on how it’s canned. Plastic bottles are rated for 18 months to 2 years or storage if unopened. Plastic containers are porous and the syrup will begin to darken and change after as little as 3 months in a plastic jug.
Those novelty log cabin tins full of syrup are cute, but you shouldn’t keep syrup in them for more than 6 months.
If you really want keep syrup in your long-term food storage, canning in glass jars is the way to go. If properly canned in sterile glass jars, maple syrup will keep indefinitely. Jars have been opened after 50 years and were just as good as the day they were stored. For best results, keep the sealed jar in a cool dark place. Even with imperfect canning practices, maple syrup should last sealed in glass for at least 2 to 4 years.
How to Can Maple Syrup
Maple syrup is naturally high in sugar and so long as it’s canned properly and sealed hot in a sterile jar, it should keep indefinitely. The biggest risk is mold spores, which will begin growing in an improperly sealed glass jar after about a year. Believe it or not, mold doesn’t ruin maple syrup. Surface molds can be scraped off the top, especially if you’re using wide mouth jars.
Begin by sterilizing glass jars. We use standard mason jars, since we have them in abundance from our other summer canning. The best way is to soak the jars in water overnight, to allow any mold spores to bloom. The spores themselves are hardy and might live through boiling. Once the jars have been soaked, boil them submerged in water for 10 minutes. Be sure to dry the jars before filling.
For canning, make sure the syrup is between 180 and 200 degrees. Below 180 degrees for packing and it may not be hot enough, but reheating the syrup above 200 degrees F can cause it to darken.
Since we don’t filter our syrup, we pack it straight from the finishing pan. That saves any reheating step and allows very hot syrup to go directly into a sterile canning jar. Leave as little headspace as possible, ideally around 1/4 inch. The lower the headspace, the more likely your jar is to seal appropriately.
Some sites will tell you to take the sealed jars and actually, water bath can them submerged in boiling water. This “canning” step isn’t actually necessary. The jars have already been sterilized in boiling water and the syrup was actually heated to well above the boiling point of water. This extra cooking step will thicken your syrup and change the color and final consistency.
Since syrup is so high in sugar and has such a high boiling point, the only “canning” that’s required is to bring it up to temperature and then pack it hot in a sterile jar. The jar lid should “pop” just like with any canned good, assuming that the headspace is around 1/4 inch. This is due to the high temperature of the syrup, which heats the air in the small headspace so that it expands. When the syrup cools, that air contracts and creates a vacuum seal.
If you’re canning store bought maple syrup for long-term preservation, the process is the same. Sterilize the jars and then bring the temperature of the syrup up to between 180 and 200 degrees and fill jars to within 1/4 inch of the top before sealing.
Storing Maple Syrup
Once the syrup is “canned” in glass jars, it should last indefinitely, but at least 2 to 4 years even with sloppy practices. Keep the jars in a cool, dark place out of direct sunlight.
Once the jar is opened, store it in the refrigerator for up to a year.
If any mold develops, just scrape it off the top. The mold is actually developing on a thin layer of water condensing on top of the opened syrup, but it isn’t penetrating down into the whole jar due to the very high sugar content.