Cinderblock Maple Syrup Evaporator

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Every year we try to improve our maple syrup operation. Last year we increased our taps from 30 to over 100 and built our own maple syrup pan. This year we’re increasing our taps from 100+ to 200 and building a new maple syrup evaporator (or cooker). The way we’re cooking off our maple sap right now works just fine but is rather inefficient. Our basic set-up is this: maple syrup pan on top of two metal saw horses inside of our fire pit with sheets of metal leaned up against the sides to try to keep heat in. It’s a super primitive way of cooking maple syrup.. like we’re some sort of animals!  We’re losing a lot of heat through the metal sheeting and therefore going through a lot of wood in the process. And we’re also losing a lot of time. It’s all fine and dandy during the day but as soon as the sun goes down, Dave and I end up taking shifts throughout the night to tend to the fire and sap. Usually one of us ends up sitting down by the fire at 2am listening to the coyotes and owls and getting so delusionally tired that we start communicating with them. So… we had to make a more efficient maple syrup cooker this year.

At first we were going to weld up a large steel box to set the sap pan on top of, but that would take a lot of fabricating and a lot of money. Then after looking around online, we saw some cinderblock maple syrup cookers which gave us a great idea. We’ll build our new cooker out of cinderblock, line it with fire brick and incorporate it into what will eventually be our outdoor kitchen. It’s going to be awesome. But we needed to call in an expert, and that expert is our good buddy Greg! He’s a madman with masonry, amongst other things. He spearheaded this whole project for us and we are eternally grateful. Because he knows way more about masonry than we sure do! We also elicited the powerful advice of His Kurtness of the legendary Cassilly Crew at the City Museum.

Greg overseeing his soon to be masterpiece
Greg overseeing his soon to be masterpiece

To start off, we leveled the site of the cooker to give us a nice, even surface. We laid out the footprint of the cooker to give us an idea for size that would work within the size of our pan and also an adjoining chimney. Once we had the footprint laid out, we filled the first course of cinderblock with concrete and anchored it with rebar for strength. In between the first and second course of cinderblock, we laid rebar parallel with the cinderblock for more strength and support. We continued this until we had four complete courses of cinderblock. We slopped the cinderblock with concrete as we went, leaving us with a solid concrete wall. While we were laying the block, we made sure to include space for the chimney that would come out the back of the cooker. And an opening for the smoke to draw up into the chimney.

Laying out the footprint for the cinderblock cooker
Laying out the footprint for the cinderblock cooker
Driving rebar into the cinderblocks for strength and structure
Driving rebar into the cinderblocks for strength and structure
Adding a space for the chimney off the back of the long side of the cooker.
Adding a space for the chimney off the back of the long side of the cooker.
This is the space we left open to allow the smoke to draw up into the chimney. Those cinderblocks in the center are just acting as a placeholder so the blocks can set.
This is the space we left open to allow the smoke to draw up into the chimney. Those cinderblocks in the center are just acting as a placeholder so the blocks can set.
Here's Dave doing an A+ tuck pointing job. P.S. Check out that sweet sweatshirt!
Here’s Dave doing an A+ tuck pointing job. P.S. Check out that sweet sweatshirt!

The next step in our cinderblock maple syrup cooker was to line the inside with firebrick. Since we’re essentially having a small, continuous bonfire in this thing; cinderblock alone wasn’t going to fly. Firebrick will protect the cinderblock from cracking and increase the longevity of the cooker. But this is where we ran into some trouble. When using firebrick outside, you’ll need a very specific type of mortar that is good for outside use. But it also needs at least 60 degrees to cure. It is also mid-Winter and we live in Missouri so… this was going to be a tricky one.

It's very, very important to get your first course of brick extremely level. Or else each consequent course will get more and more out of level and you'll end up with a crooked, uneven wall. It'll be horrible. Take your time and pay attention to that level!
It’s very, very important to get your first course of brick extremely level. Or else each consequent course will get more and more out of level and you’ll end up with a crooked, uneven wall. It’ll be horrible. Take your time and pay attention to that level!
The beginning of the firebrick
The beginning of the firebrick

To set firebrick for an outdoor use you’ll need a refractory castable cement. You can find this at most fireplace stores, but it can be pricey or not be available in larger quantities. However, it’s worth it in the long run. If you don’t use this specific mortar, it won’t set up correctly and you’ll end up having to replace a whole bunch of firebrick and you’ll feel like a big loser. Don’t be a loser. Just bite the bullet and get the right stuff. We tried using the mortar for indoor use and it was a huge waste of time, so trust us. Don’t be sad losers like we were. We ended up finding a refractory cement manufacturer near us that traded us old bags for maple syrup. Perfect!

We started setting the firebrick on the inside of the cooker and chimney by using the refractory castable cement for outdoor use. We also used brick ties to help set the bricks together. You grind a slot into the cinderblocks, insert a brick tie into the mortar joint in between the courses of firebrick. This creates a mechanical connection between the bricks and the cinderblock wall that they are mortared to instead of only relying on the mortar to hold the bricks to the cinderblocks. Once we got a few courses formed and tuck pointed, we had to make sure it was going to set in the midst of February temperatures. We made a small fire in the pit of the cooker to warm the mortar and bricks and that helped the bricks set up nicely.

Firebrick is almost completely cured
Firebrick is almost completely cured

While the firebricks were setting up, it was time to figure out the chimney. As previously mentioned, we made sure to leave an empty space in the face of the cooker’s long side to allow for a draft. Setting the chimney slightly behind the cooker will leave plenty of room for the maple pan, and stay out of the way for foot traffic and such things. The chimney itself is a triple wall pipe (found at any farm supply store or store that sells wood burning stoves) topped off with a rain protector thingy. We’ll probably install some sort of butterfly damper to control the amount of draft and what have you.

This is the space left open for the the smoke to draw into and up into the chimney.
This is the space left open for the the smoke to draw into and up into the chimney.

Now for the front, eventually we’ll fabricate some steel doors out of 1/4″ plate onto the front but for this year, we’ll just lean up some corrugated sheeting across the front to keep the heat inside the cooker. On the bottom of the cooker we’ll build a grate out of angle iron or rebar to allow air to get underneath the fire. The last thing we had to do was to see how level this thing really is with the pan. Lo and behold, it is actually level!! With a slight angle toward the front to allow for the finished syrup to drain at the proper angle through the pipes. It was truly amazing that we made something actually level on the first try. And with that, the cinderblock maple syrup cooker is ready to go for its inaugural cook this weekend!

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Ta-da! Our new maple syrup evaporator complete with chimney and corrugated metal on the front!
Ta-da! Our new maple syrup evaporator complete with chimney and corrugated metal on the front!
The finished maple syrup cooker!! Ready for a big fat fire and hundreds of gallons of sap!
The finished maple syrup cooker!! Ready for a big fat fire and hundreds of gallons of sap!

The great added bonus of this maple syrup cooker is that we’ll be able to use this cooker for SO many other things. We can remove the pan, make a griddle for a cooktop in the summertime, make a rotating spit for whole chickens, pig or whatever. There’s lots of great options for this basic outdoor kitchen cooker.

Stay tuned on our facebook page for our first maple syrup cook on our new evaporator!


One Response

  1. March 30, 2015
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    […] to a thick, snotty and sour mess. So that was a loss. Then we were finally able to cook on our new cinderblock maple syrup cooker, but everything around it was a huge mud pit. Then, as we were doing our final finishing cook on […]

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