Maple syrup is finished when it reaches at least 66% sugar (the sap starts at 2% sugar). At that concentration of sugar, the syrup boils at 7 degrees above the boiling temperature of water – that’s how we can tell we’re getting close to the end. Yes, that normally means 219 degrees, but altitude & atmospheric conditions can change the exact temperature. So we calibrate the boiling temperature of water first, using a digital thermometer to get an exact reading. Then we use the same thermometer to periodically check the syrup temperature in the boiling pan.
The finishing step requires a more precise temperature control than the wood stove can provide, so when the sap gets to within a degree or two of the desired temperature, we drain it into a big stock pot and finish boiling it on the burner of our turkey deep fryer (outside!) so we can more closely control the temperature. Don’t worry - there’s no deep-fried-turkey aftertaste to our syrup! To get a more precise estimate of the sugar content in this stage, we use a hydrometer to measure the specific gravity of the syrup. As the sugar content gets higher, syrup gets thicker, and the hydrometer floats higher. Whatever you do, don’t try this on the kitchen stove. A friend of ours tried it once, and spent less time boiling than she did cleaning maple syrup droplets off the stove, the counter, the floor, the microwave, the exhaust hood, the dog…
