Instructions on making a do-it-yourself homemade maple syrup evaporator for maple syrup making.
Many backyard evaporators are built from concrete blocks. A firebrick liner stops heat damage. Steam-table trays, like those used for buffets in restaurants, make ideal evaporator pans.
Before starting construction on your homemade maple syrup evaporator, gather the materials and build a mock-up of the evaporator, placing the concrete blocks and firebrick just as they would be in the completed firebox, without mortar. By making a mock-up, exact dimensions can be worked out and problems corrected before the actual construction.
The width of the firebox depends upon the length of the steam-table trays and should be built so that the lips of the pans rest upon the edge of the firebrick.
The length of the firebox is determined by the combined width of whatever number of pans you decide to build into your evaporator, which in turn depends on how much boiling capacity you think you will need. It takes about 100 square inches of pan surface to boil off one gallon of water per hour. Steam-table trays are approximately 12 inches by 20 inches, or 240 square inches, which means each pan will give you approximately two gallons per hour of boiling capacity. I opted to use five of these 12-inch-wide trays in my evap — giving me ten gallons per hour of boiling capacity — and so my firebox needed to be 60 inches long.
As for the height of the firebox, I made mine three blocks, or 24 inches, high. Make your firebox too high, and you'll need a massive fire to sufficiently heat the pans; too low and you'll have a difficult time loading the wood and tending the fire.
Adding a fire door and draft control means better control of the boiling and a hotter evaporator. A fire door can be as simple as a piece of sheet metal leaned against the firebox or it can be as complex as a 1/4 inch steel plate on hinges with damper openings.
The flue can be run from the tap or the end of the evap, but in either case should extend above the roof of the shed or sugarhouse, or else ash will fly back into the boiling syrup.
To use the variable capacity, fill all the pans with sap to start boiling. As the sap boils down, pour the low pan into the remaining pans to bring their volume back up. Refill the emptied pans with water so they won't burn or warp. Continue the boiling until one pan of sap/syrup remains. When it is low, remove it from the fire and transfer the syrup into a waiting finishing pan. Finish off the syrup on a well-regulated heat source such as a kitchen stove.