That's not incuding the 2 quarts we made last week, cooking it for five days over a fire. That syrup turned out much darker, with a more molasses-y and very smoky taste: good, reminiscent of camping, but not what we expected.
Some people use outdoor electric turkey fryers to boil down the sap, and I decided to investigate that option. I found this boiler/fryer that seemed to be even better than a turkey fryer because it has more surface area for evaporation and we can potentially use it for other purposes, such as cooking sweet corn for a big picnic, hosting a fish boil, or perhaps scalding chickens after butchering.
It worked fabulously. Much less work and much less smoky than feeding a fire, and much more efficient boiling. When you first pour the sap into the pan it is clear like water, then turns cloudy and gradually becomes deep amber. We filtered out any particles (bark) before boiling and skimmed off the foam. We finished off the boiling in the house, bringing the syrup to 220 degrees F.
We have boiled about 37 gallons of sap from two big silver maple trees and it has taken 1 1/2 tanks of LP gas at $19/tank.
For breakfast this morning we feasted on waffles with our homemade syrup. It is very delicate, intensely sweet, with a slight vanilla essence.