The Grovestead

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Category: Evaporator

Evaporating sap and making maple syrup

Evaporator boils down the sap

The trees are tapped and the sap is flowing. Finally its time to turn those gallons of sap into delicious maple syrup! If you have not already read part 1 and part 2 of this series you may want to go back and do that first. In this post I’ll cover the evaporating process and finishing and bottling maple syrup.

Evaporating the sap

By far the most time intensive part of maple sugaring is the evaporating. Sap is 98% water, give or take, so depending on your setup you can spend many dozens of hours and an obscene amount of wood getting the sap boiled down to syrup. The last two years I hodgepodged together a cinder block evaporator. It worked, but was terribly inefficient and a bit dangerous. This year I had plans to build my own steel box evaporator and lucked out when a local welder offered to sell me his own at a great price.

Wood-burning firebox

The firebox holds a tremendous amount of wood and the stainless steel pan can hold up to 15 gallons of sap at a time, although it is more efficient to boil a shallow than deep pan.

The goal is to keep a roiling boil for hours on end. Because it takes so much wood and takes so long to get everything heated up, I usually wait until I have 20 gallons of sap collected before evaporating.

Sap vigorously boiling on the evaporator

The time required varies greatly by the weather. Colder, windy days take longer than calm, sunny ones. Next year I’ll make better use of firebrick and concrete blocks to insulate the steel from the wind and focus as much heat as possible to the bottom of the pan.

While the sap is boiling I have a second pan warming sap on the edge of the evaporator. Pouring cold sap into a boiling pan would kill the boil and slow down the evaporating. So everything you can do to pre-heat the sap saves time in the end.

Warming pan warms up the sap before being added into the main pan

As the sap boils impurities foam up to the surface. Every so often I use a strainer to scoop off the foam.

Straining foam out of the sap

That’s pretty much all there is to it. Feed the fire, add sap, strain. Repeat. The evaporating is done when the sap is reduced to a dark brown color and the sap/syrup is thickening. It’s usually pretty obvious when the consistency of the sap has changed.

Sap is reduced and ready for finishing

Because the final stages of evaporating need to be tightly controlled, most people will “finish” the sap indoors on a standard range.

My new evaporator has a nifty drain spout. To get the sap/syrup out all I need to do is turn the spigot.

Draining the syrup out of a spout on the evaporator pan

Finishing the sap

The final stage of making maple syrup involves getting the syrup to the right consistency. There are a couple of ways to do this. You can either measure the buoyancy with a hydrometer or use a candy thermometer to measure the boiling temperature. The boiling pot has to be watched closely because once the sap turns to syrup it can boil over quickly. I lose lots of syrup this way every year, despite my best efforts.

I like to boil at a medium-high heat taking periodic measurements with the hydrometer.

Hydrometer measures the density of syrup

Periodic checks using the hydrometer ensures the exact right density

Measuring 32 baume on the hydrometer means the syrup is done

After ladling syrup into the cylinder container, I drop the hydrometer in and it floats to the measured density. A reading of 32 Baume (or 66 Brix)—the red line—means the syrup is done. Alternately, a candy thermometer reading of 7.1 degrees above the boiling point of water (219.1 for most of us) is considered finished syrup.  It’s important that the measurements be accurate, otherwise the syrup may be too weak and not store well or be too dense and crystalize. That’s why finishing inside on a controlled stovetop is preferred.

Filtering and bottling the syrup

Now the syrup is complete and ready to bottle. First the syrup needs to be filtered. Some people use cheesecloth, but I prefer a dish towel folded in half (used only for maple syrup). In my experience cheesecloth is too porous and allows too many particulates through.

Filtering the finished syrup

I can usually filter 2-3 pints at a time into a 2-quart bowl. Then I pour into pre-sterlized canning jars and screw on the lids.

Pouring filtered maple syrup into jars

Syrup does not need to be sterilized in a water bath like other canning products. As long as the containers are sterile the boiled and filtered syrup will remain extremely hot for a very long time and create a tight seal as they cool down. Tip: screw the lids down as tight as possible, then the next morning screw them a little tighter, if you can. I’ve had some jars lose their seal days or weeks later, presumably because the lids were not as tight after everything cooled down.

When you do open a sealed jar, it has to stay in the refrigerator from that point on. Pure maple syrup is different from the brown-dyed corn syrup you find in the grocery store and will spoil if not refrigerated after opening. Properly sealed syrup will last at least one year, but likely won’t make it that long once you have a taste for it.

Last step: cook up some pancakes and enjoy.

Enjoy your pure maple syrup with pancakes and a good cup of coffee.


Maple Syrup now on sale!

UPDATE: We sold out of our maple syrup on the first day–thank you to everyone who ordered a jar, we appreciate your support!

Evaporator boiling maple sap

We just finished a fresh batch of Maple Syrup tapped from our own trees here at The Grovestead. Last year we had intended to sell some jars to help recoup the costs of making it. But time got away from us, and we ended up enjoying it ourselves and giving some away as gifts.

Jars of Maple Syrup

This year we have set aside a portion of our “crop” to sell. If you are interested in tasting 100% pure Maple Syrup from our own trees, please visit our Store page and order a jar!

Last of the sap

Evaporator at Night

It’s been many late nights but I finally finished evaporating this year’s Maple sap. We collected 65 gallons this year and it took on average one hour to evaporate five gallons. That doesn’t include an hour to scrounge for wood, build the fire and get the coals hot enough to boil water. So, all in about 16 hours outside, tending the fire.

At first, I love it. I’m outside, enjoying a warm fire, making syrup from my own trees. What could be better?

About 8 or 9 hours in I begin to think “there’s got to be a better way…” and schemes for next year’s improvements begin churning in my head.

Then around the 12th hour I figure the fire can watch itself for awhile. But minutes later I look outside to see flames leaping from one of the pans.

Evaporator burnt syrup

Five gallons of sap boiled to a crisp and then ignited.

No, the evaporator demands my full attention. So I dutifully kept it company until all the sap was done.

How to Build an Evaporator (from stuff laying around)

Boiling maple sap over home-built evaporator

Through a good amount of trial and error last year I figured out how to construct an evaporator to boil down our maple sap on the cheap. Then I forgot how I did it. So this year I’m documenting the construction.

This plan uses about a dozen concrete blocks and was designed to fit the 5-gallon buffet pans which I use to hold the sap. These are the same style pans you see at Chinese buffets holding the cream cheese wontons. It’s not as efficient as production-scale evaporators, but does the job. And the price is right (free, in my case).

Step 1
Laying the first level of concrete block

Find a level site that won’t be growing anything for the next 24-36 months. Layout the first layer of block to the width of the pan.

Step 2
Chimney footing

Align rear blocks to leave a gap for the chimney block. You might want to set the rear blocks up on spacers so the exhaust intake is higher off the ground (this will make more sense later).

Step 3
Lay the second layer of block

Add the second layer of blocks on top of the first. I built this evaporator to accommodate two pans, but you could easily extend it to support three. One block (the chimney) should span the two rear blocks so that you see straight through to the ground from the top.

View of chimney from top

Step 4
Fill in cracks

Use another block to cover the open space below the chimney block, and use a couple bricks to cover any gaps around the chimney. It’s not going to be airtight, but anything you can do to contain the fire and keep it on the pans will improve efficiency (less fuel, faster evaporating).

Step 5
Set up chimney

Create a chimney flue at least a couple feet above the top of the chimney block. I used old tiling we found on the property. But you could use any kind of ducting or even a few more concrete blocks stacked vertically. The idea here is to vent the exhaust away from the pans. Simply boiling the sap over an open fire would cause a lot of ash and soot to land back into the sap.

Just beware, the exhaust coming out will be extremely hot! As you can see from the flames coming out of the top on the first photo — it looks like a jet engine!

Enjoy the fire!Building an Evaporator - Start a fire

Finally, light a fire and pull up a chair. I usually wait a good 20-30 minutes before I have enough coals to put the pans on and start boiling sap. After that I just keep feeding the flames. It always amazes me how much fuel it takes to evaporate sap.

Evaporator pre-warming sap in separate pan

I can shave a little time off the process by pre-warming sap in a separate pan over the second chimney hole. Just keep in mind you’re boiling away 98% water, so it’s going to take awhile. In my experience, it takes about an hour to boil 5 gallons.

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