The other day I stumbled across a web site showing how to build a “rocket stove” which is two pipes that meet at a 90 degree angle – one vertical, and one horizontal. These pipes are then set inside a metal bucket, and the space between the bucket and the pipes is filled with sand. Fuel and air are fed into the fire though the horizontal pipe, and the flames, heat, and smoke go through the vertical one. The sand holds in the heat to make it very hot.
When I saw it, it reminded me of a Dakota fire. This is made by digging a hole straight down in the ground, and then digging a smaller diameter hole angling down so that they both meet at the bottom. Fuel and air are fed through the diagonal hole, and the heat and smoke go out the vertical one.
Since I have about five gallons of sap to boil down into syrup, and lacking a large metal bucket, I thought I’d give the Dakota fire a shot at it. Not that anyone uses a rocket stove to boil sap.
We have about a foot of snow in the backyard, so I shoveled out a spot to work and chiseled through the frozen ground (it was only frozen for an inch or two). Then I dug the Dakota hole, lit a fire in it, and set a big pot over the flame. Va gave me a pot. She doesn’t care if I make it suety, so I’m in the clear there.
I didn’t have the lid on the pot for very long, but it was on there when I took the photo. It would be hard to evaporate sap with a lid in the way holding all the steam in.
The fire did burn pretty hot, and I spent the whole afternoon feeding it sticks. But by the time it got dark, the sap had not been reduced by more than an inch or so. I took the kettle off the boil, let the fire die down, and went in the house for the night.
Since it took all afternoon to get it to go down one inch, I decided to just do it inside. I used a different pot since I didn’t want to get the stovetop all suety. I reduced the sap by another three inches or so, but I noticed that instead of smelling like syrup, it smelled like smoke. Since smoke is largely solid particulate matter, and since solid particulate matter does not evaporate, I reasoned that the smoke in the sap would just get more and more concentrated. Which is something I did not want. So I dumped it out.
The trees are making plenty of sap though, so five gallons is not a major loss. And I learned something.
Don’t use a Dakota fire to reduce sap unless you can rig up a chimney somehow.