Solar Powered Maple Syrup

An easy, sustainable way to make maple syrup for family and friends, without the bother of burning wood or the bummer of burning fossil fuel, is to boil sap in a steel pot on an induction hot plate, plugged into an outdoor outlet at a solar-powered house. This method has allowed me to use our solar energy to make maple syrup. While our sap is boiling on our patio all day, I can be doing other things, making the whole process much more “doable.” In my experience, using hot plates is simpler, cleaner, faster, more convenient and more efficient than burning fuel to boil sap.

One nice thing about an induction plate is that it is portable and easy to use. It plugs into any regular outlet. If your house or camp has solar panels, then the electricity used for the induction plate is being generated from sunshine.

Another great thing about induction cooking is its efficiency. This cooking technology uses a magnetic field to heat up the pot itself. This transfers energy to the sap so it boils quicker than it would with older types of electric heat. Compared to burning wood or fossil fuel to heat a pot to boil sap, induction is much more efficient.

As the price of solar panels continues to fall, I’m interested to see how the economics of making maple syrup with clean energy will compare to the traditional methods of burning fuel. For me, the hassle factor alone isn’t worth it to burn fuel -- it is nice to just plug in and boil with no muss and no fuss.

But probably the best part of boiling with induction is the incredible control. As you get closer to being done, you can dial down the induction plate power and make even just a few ounces of syrup without burning them. It’s almost magical to start with what looks like water and end up with delicious maple syrup!

Necessary supplies:

• one or more maple trees with a trunk at least 32 inches in circumference four feet above ground
• tailor's tape to measure circumference of tree trunks
• cordless drill
• 5/16" and 7/16" drill bits
• metal taps (5/16") or plastic taps (7/16")
• rubber mallet (to tap in taps)
• claw hammer (to remove taps)
• food-grade tubing 7/16" outer diameter, 5/16" inner diameter
• food-grade 5 gallon bucket with lid (or other containers, such as milk bottles for collecting sap)
• 10-liter stainless steel pot that works on induction stove (for boiling sap)
• mesh strainer to pour sap through to strain out bugs, leaves, etc.
• saucepan that works on induction stove (for finishing syrup)
• 1800-watt plug in portable induction hot plate
• wire filter frame to hold filters when pouring boiling sap through
• two paper pre-filters for filtering out impurities
• one felt final filter for filtering out niter
• honey refractometer to test when syrup is done
• glass mason jars, metal lids and bands to store syrup

First, you need a maple tree or two that has grown big enough to tap. I identify maple trees by their leaves, but apparently it is possible to find maple trees in the winter looking for opposite buds on twigs and inspecting bark. Just be aware that ash and dogwood also have opposite buds on their twigs. A tree with a trunk that at four feet above ground is 10 inches in diameter (which equals about 32 inches in circumference) can be tapped.

Several varieties of maple trees can be tapped. From what I've read, sugar and Norway maples tend to have the highest sugar concentration in their sap, followed by black maples and then red maples and silver maples. I'm not picky about which species of maple I tap; I just try my best to avoid tapping oaks and ash trees.

Last fall while the leaves were changing I went out to our land with a tailor's tape measure, found some maple trees by looking at their leaves, checked the circumference of trunks four feet off the ground, and tied yellow ribbons around the ones that had a round girth of 32 inches or more. Going back in the winter after the leaves are off, I’m honestly not sure I would have been able to tell the difference between our ash trees and our maples. I must be tree blind, because my friends can see a difference in bark between the maples and ashes. In any case, if you want to be sure what you’re tapping, a fall expedition is worthwhile to identify your maples beyond doubt.

After identifying my maples, the next thing I did was gather and acquire maple syrup-making equipment. See above for the complete list of everything I ended up needing.

If you’re tapping trees in Maine, you’ll want your equipment on hand before the end of February. The maple season may be earlier or later in your neck of the woods.

I got food-grade plastic 5-gallon buckets with lids for free from Big Top Deli in my hometown of Brunswick, but my older son said they made the syrup taste like pickles. So we switched to collecting sap in empty Smiling Hill Farm glass milk containers. I used a 7/16" drill bit to make holes in the lids that 7/16" outer diameter plastic tubing fits snugly into. On our property, we get flies in our sap if we don't collect in containers with snug lids.

In my experience, you don’t need thermometers or hydrometers. Maple sap starts out around 2% sugar content and needs to end up between 66% and 68%. The boiling temperature and density of the solution in theory should tell you the sugar content so you know when you’re done, but a refractometer is a more direct way to measure sugar content.

In my experience, a thermometer is not helpful. First I tried a regular candy thermometer and then a fancy digital thermometer, but I was never able to use boiling temperature alone to make good syrup. According to my thermometers, my sap boils at 211.5 F. So in theory I should have syrup when the solution’s boiling temperature is 219 F. What happens in practice is when I let the pot boil until the temperature reads 219 F, I never know what I’m going to get: either sugar content too high (which makes thick syrup that crystallizes as it cools) or too low (which makes thin syrup that goes bad unless refrigerated).

With a bigger batch of syrup I could float a hydrometer to measure density and infer sugar content, but with the small amount of syrup I’m making, a refractometer is the better tool. A drop on the refractometer reveals the sugar content of the batch.

Once you have your syrup-making equipment on hand, you’ll need to decide when to start drilling holes in your trees. Sap flows up and down the tree when temperatures rise from below freezing to above. This happens occasionally all winter in my part of Maine, but starts to happen more often and more consistently at the end of February or beginning of March.  You want to finish your sap collection before the tree buds start swelling; after bud swell, sap makes syrup that doesn’t taste good.

You’re aiming for at least a four-week maple syrup season, and maybe five or six weeks, before the tree buds out, when the temperature often fluctuates from below to above freezing. When you wound a tree by drilling 1.5” to 2.5” into it to collect sap, you have about four to six weeks before the tree can heal itself. Once the tree has healed its wound, you won’t get more sap even if it is flowing from the tree’s roots to shoots. After you’ve tapped your trees, whether you get sap and how much depends on the weather.

During freezing weather after a thaw, maple trees suck up sap from their roots to their twigs. When the weather thaws again, sap flows back down to their roots. You get the best flow when the temperature swings from the twenties or below to the forties or above. Sap can flow for a few hours or days depending on the parameters of that freeze-thaw cycle in the micro-climate for each tree. On our property, one tree can produce more than a gallon of sap in a day. Plan your collection strategy accordingly.

In 2022 I drilled my first taps on the weekend of March 5 and 6. We had a few good days of sap flow, then a warm stretch between March 17 to 22 when we collected almost no sap, and then a great couple of days on March 23 and 24 when our collection jars overflowed. You just never know what the weather will do.

Unless you’re planning to tap dozens of trees, I recommend you use a simple collection system of one bucket or jar on each tree. Here’s the plan I followed:

1. Decide how many trees you want to tap.
2. Get a bucket or a milk jar for each tree.
3. Drill a 7/16” hole in the plastic lid for each bucket or milk jar.
4. Cut a piece of tubing long enough to reach from the tap to the ground. Thread the tubing through the lid (it should be snug).
5. On a day above freezing, carry a tap, a rubber mallet, tubing, a lid and a collection bucket or jar to each tree.
6. If you’re using metal taps, drill a 5/16” hole 1.5” to 2.5” deep into the tree. Angle this at a slight incline (so sap will flow out). For plastic taps, drill a 7/16” hole. An easy way to drill holes the right depth is to put a piece of tubing over your drill bit, leaving just the length of bit exposed that you want. A study I read indicated very little difference in sap flow between a hold 1.5” deep versus 2.5” deep.
7. Use the rubber mallet to seat the tap. (This works better on days above freezing.)
8. Push the tubing onto the tap. Put the lid on the bucket or jar on the ground. The tubing should go from the tap, through the lid, into the bucket or jar.

Once you have tapped your trees, wait until a day when sap should be flowing. Then go out and check your buckets. You should see clear sap that looks like water and tastes clean with just a hint of sweetness. You want to collect this sap and store it in a cool place until you can boil it down (storing sap in a bucket buried in a snowbank is a great option if you still have snow).

This year I’m getting about one pint of syrup for every 20 liters of sap. You can decide how often you want to boil based on how much sap you are collecting and how much syrup you want to make in one batch. When I’m ready to boil down sap to make syrup, here’s what I do:

1. Get my induction hot plate plugged into an outdoor plug at my house. (Since my house has solar panels on it that produce electricity during the day, this keeps the whole process solar powered.)
2. Put a 10-liter pot on the induction plate.
3. Pour about 10 liters of sap through a metal strainer into the pot. This catches bugs, leaves, twigs, etc.
4. Leave the pot uncovered, turn it on, and crank it up to full power to boil.
5. If I have enough sap, I’ll keep adding as it boils down, until I’ve put 20 liters into the pot.
6. Let it boil down to less than 2 liters.

If I've started with twenty liters, by the time sap is boiled down to two liters (i.e. a 10 to 1 reduction) I'm ready to set up for the transfer to my finishing pot. This is a smaller saucepan that I'll use to pour finished syrup into canning jars.

Here's what to do once you're ready to transfer boiling sap into your finishing pot:

1. Set up a filter wire stand with one pre-filter in it, over a smaller pot.
2. Take the 10-liter pot off the induction plate.
3. Pour the boiling hot sap from the 10-liter pot through the filter into the smaller pot.
4. Put the smaller pot on the induction plate and start boiling it.

Then take the pre-filter and the 10-liter pot inside to rinse out. If you rinse out the pre-filter right after using it, you can re-use it several times.

Finish the syrup in your finishing saucepan on the induction hot plate.

1. Boil down to less than 1 liter.
2. Turn down the heat settings when the pot starts boiling over.
3. Set up the filter wire stand with the felt filter lined with a pre-filter, over a mason jar. Have a lid and band handy to seal up the jar once it’s full of syrup. The paper pre-filter should be inside the felt filter so solids and foam get filtered out by the pre-filter and don't come into contact with the felt filter.
4. Start taking sugar measurements with a refractometer when you're close to the amount of syrup you expect. If you start with 20 liters of sap, expect about 500 milliliters (half a liter) of syrup. The ratio is usually about 40 to 1 sap to syrup.
5. Use a spoon to get a drop of boiling sap and put it on the honey refractometer. Look through it to see the sugar content of that sample. In my refractometer, through the viewport the sugar content will be a white area from the bottom and the top will be blue. The solution will start off all blue and then the white area will grow from the bottom.
6. Once the boiling solution is at 66% sugar content, take the pot off the plate and pour the boiling hot syrup through the pre-filter and filter into the mason jar.
7. Seal up the mason jar while it's hot.
8. Rinse out the pre-filter, filter and saucepan.
9. Unplug and wipe off the induction plate with a sponge.

After you've poured syrup into your mason jar and sealed it up, as it cools the lid should seal shut. I like to label the lid with the source of the sap, the date and the sugar % of the batch.

If the lid doesn't seal shut, no big deal. You can keep maple syrup in your refrigerator. You can also reheat your syrup and try again to reseal the mason jar lid.

Check with your local extension service if you have questions about home-made maple syrup and food safety.

If you've boiled to 66% or 67% sugar content, your maple syrup should be safe to store unrefrigerated in your sealed up mason jar. If you're below that sugar level, best to store it in the fridge. Or you can boil it so more to reach 66%. If you boil past 67%, you can add water and keep boiling the diluted solution until it's in the 66% to 67% range. If you boil past 68% and let the maple syrup cool, it will solidify into maple candy. It's all good!

Once temperatures are no longer falling below freezing, or if it's been six weeks since you drilled holes into your trees, or you notice maple buds starting to swell, it's time to take out your taps. A claw hammer works for me to remove both metal and plastic taps. Rinse out your taps, collection buckets, and tubing with water. Store for next season and start scouting for more maple trees!