The Walden Effect: Farming, simple living, permaculture, and invention.

Concentrating maple sap through freezing

Tapping a sugar maple

When I posted about the potential for feeding maple sap to bees, two of our readers made the suggestion of utilizing freeze concentration to increase the proportion of sugar in the sap without causing bee indigestion by heating the sap to the boiling point.  Mark thought I was breaking the laws of physics until I explained that freeze concentration is just a method of separating most of the sugars from some of the water, resulting in a smaller quantity of liquid that's sweeter than what you started with.

Depending on who you talk to, you can capture 70% to 90% of the sugars in maple sap in 16.5% of the volume through one to two rounds of freezing and thawing.  If your area gets below freezing at night, simply leave your sap outside or, if you're enjoying a warm spell like we are, put a bucket of sap in your chest freezer overnight.  After freezing, let the Concentrate maple sap by freezingblock of ice sit at room temperature until about a third of its bulk has melted --- that's the precious sugar portion.  Toss the ice and put the sugary sap back in the freezer for a repeat freeze-thaw cycle, this time keeping the first half of the melted liquid.  The result should be a liquid that has increased from 1-3% sugar to 5-16% sugar.  (You'll also have some frozen sap-water to turn into Appalachian ice sculptures.)

According to some sources, freeze concentration is a great way to start making maple syrup, as well as for concentrating maple sap for bees.  Freezing generally uses less energy than boiling off the same quantity of water (especially if you can just put your sap outside to freeze), and you won't have to deal with the excessive steam clogging up your kitchen.  However, scientists recommend planning on utilizing boiling to turn your sap concentrate into a real maple syrup since the chemicals that produce the color, flavor, and odor of maple syrup are formed through the application of heat.  Plus, you need to get rid of enough liquid to bring your sap to at least 66% sugar when making maple syrup, which would take quite a few rounds of freezing and thawing.

We'll be trying out our first batch of maple-sap concentrate on our bees, but will boil the next batch down into syrup on top of our wood stove.  Stay tuned for more information in later posts.

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.

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Hey Sweetie, so I just read this article about maple sap. Apparently, they've just figured out that sap goes up rather than down. They collected more sap from the tops of the maple trees than from the bottom. I read about it in the week, which probably means the full article appeared elsewhere.
Comment by Heather Thu Feb 20 14:52:26 2014
For the record I knew Anna was not "breaking the laws of physics"'s just one of my favorite sayings from the old Star Trek when Scotty admonishes Captain Kirk in his endearing fashion.
Comment by mark Thu Feb 20 16:00:45 2014
Reading about concentrating maple sap by freezing brought to mind my experiences at the old ice plant (working there was kind of a 'rite of passage' for my family... my grandfather worked there for 51 years). Ice was made in 300 lbs blocks by putting fresh water in rectangular "cans" and suspending them in a large vat of refrigerated brine. A tube was suspended in the center of the can and air pumped in. The bubbles rising in the middle would cause the water to circulate. Impurities would concentrate in the middle of the can as water froze at the outer edges. Just before the "core" froze, it was sucked out, the tube removed and fresh water added. Perhaps a similar process could be done with the maple sap using a cheap aquarium pump and tubing.
Comment by George Fri Feb 21 13:59:41 2014

Your website came up in a google search so I read the article. The very reason I was searching is because I had tapped and produced about 60 gallons of sap this year but in Minnesota our first sap run was only a week and the temps fell hard to negatives and my sap froze in place. I brought the buckets of ice inside my house and let them thaw before boiling out the water. They took quite awhile to thaw, about a week. My daughter likes to taste the sap right in a glass of water so like usual, I let her have a glass.

The look on her face was one of confusion as she had brought friends out from the neighbors and had bragged up how good the water tastes. I then tried it and sure enough it tasted of plain water. No Maple flavor AT ALL.

I opened more sap buckets and all had the same result. I was thinking maybe sugar levels were low in some trees etc.

One of the girls said, I wonder if the sweet water is at the bottom. I was about to say, no, that doesn't make sense, when I decided to test her theory. 10 year olds have awesome insight. So I poured half a 5 gallon bucket out slowly and let the girls dip their glasses again. Their faces lit up. Sweet maple sap!

I then took a spoon and stired one of the other buckets we had tried, it was now sweet again.

So, here I am on the net trying to find evidence that we were onto something! Separating the maple sugar from the water by freezing. Alas your post didn't confirm it as my maple sap was totally thawed. I do have a theory that based on your article, the sugar water, if cold enough sinks as it would be heavier and since it freezes last, it must thaw at a different rate as well in a layer! If undisturbed one in theory could pour off the top!

Now to test!!!

Comment by Ian Osborne Mon Mar 20 21:02:55 2017

I don't know if Ian Osborne will ever see this, but in case someone else reads through and comes upon his daughters' insights, what happened is the creation of a density gradient. It's not uncommon and is surprisingly stable in liquids.

As the ice in your buckets melted, the part containing the bulk of the sugar melted first, yielding a relatively dense, sweet liquid. The later, nearly pure, ice slowly and gently melted over the top of it, creating a second layer of less dense water. Given several days to sit, the two layers would eventually diffuse into one another. If this were done in a clear container you'd even be able to see the different layers because of the difference in the way that they bend light.

It will never happen in the other direction though; you won't get the sugar at the bottom of the bucket by allowing it to be still and cold. That requires some significant outside intervention (freezing, R/O filtering, boiling, that sort of thing.)

You've likely seen something similar if you've ever put sugar in a glass of iced tea and not stirred. The sugar dissolves in the tea at the bottom of the glass and it makes a layer of syrup that flows around the bottom as you tip the glass back and forth, but it doesn't readily spread throughout the rest of the glass without stirring.

Comment by Jason Patterson Sat Dec 9 23:40:00 2017
You can increase the sugar concentration of your sap by removing ice from your sap, but you will lose some sugar in the process. I have melted the ice that was removed from sap and measured the sugar content using a Brix meter. What I have found is there is between 0.75 - 0.5% sugar that was in the ice. With the low concentrate sap that I get this means if I were to throw out the ice I would be losing 20% or more of the sugar/syrup. If I had an overabundance of sap it may be worth the trade-off, but for me it is not. Here is another article from someone else who came to this same conclusion
Comment by Antony Thu Mar 15 13:04:07 2018
I'm not sure what I did wrong, but I attempted to use the freeze-thaw method to get a more concentrated sugar-sap liquid. The sap straight from my maple tree has a 3% sugar content. I froze a 3 gallon bucket of sap, then brought it out to thaw about 1/3 of its volume. I removed the ice chunk from the bucket and saved the remaining liquid inside. I then re-froze it and let it thaw again - this time 1/2 of its volume. I then removed that ice chunk from the bucket. When I measured the remaining liquid - it was now at only 1% sugar content! Eek! Anyone have any theories on what I might have done wrong?
Comment by Anne Sat Mar 13 13:57:34 2021
Do not freeze solid. I lifted of 50% ice and thawed it, measuredd 0.2 % +- ' boiled down to less than one teaspoon syrup, TASTELESS. The other half boiled down to 1/2 cup of good syrup.
Comment by Dave R Mon Mar 15 21:14:00 2021

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