You probably heard the term "Liquid Gold" in lots of different context e.g. oil, the melted precious metal, water in the desert, etc. Here in New England, when winter's breath is shallow, and spring has not yet woken up, liquid gold has a distinct meaning. It's the magic that happens when you pierce a maple tree to draw its juice, and boil it until the sugar content reaches 66-67 percent to create maple syrup.
This weekend, Kimberley and I had a great time creating our very own liquid gold. We tapped 7 trees with 12 taps, and collected about 35 gallons of maple tree sap. Boiling the sap in a home made evaporator, kept us occupied over both days. I'm just about to finish the process on our kitchen stove. I expect 4-5 pints of the finished product today.
Here comes the science bit. Sap turns into maple syrup when the boiling point reaches 7.1 degree Fahrenheit over the boiling point of water, which is dependant of your elevation and local barometric pressure. Today, at our home this is 216 degree Fahrenheit.
The not so scientific approach, is to stick a cold spoon into the boiling sap and watch it drip from the spoon. If it is "sheeting", your syrup is ready. Of course licking the spoon is part of the process, which makes this my preferred testing method.
For centuries, alchemists tried to turn all kind of materials into gold without success, when all the time the real liquid gold was just a boil away.