Hello everyone,
I live in Vermont and this time of year when the weather is warm in the sun, and cold at night we make maple syrup. I did this last year for the first time, and I had a great time realizing the interesting mechanics of  how it is done. First of course you need maple trees, Lots O maple trees!  We drill a hole into the tree trunk, about 4-5 feet off the ground, the hole is 7/16th and about 1.5 inches deep, at a slight upward angle. Then we install a tap, which is a hollow metal spike with a hook attached. Then hang a bucket with a lid on the hook and wait!
Once we have about 400 gallons of raw sap, we can make about 10 gallons of syrup. The material in the tree, which is basically glucose, is a raw sugar. Like most raw sugars, this can be processed into a refined sweet product. Beets, cane, corn, and many other plants produce sweet sugars. Some plants do not yield sweet products, and it depends on the biology of the plant.
Maple trees extract a vast amount of water from the soil in spring to fuel the leaf growth process. When these trees do this, we call it a run. A tap can produce 2.5 gallons in a good day. That is a lot of sap moving up into the tree, and most of this material is water. It takes about 40 gallons of sap to make one gallon of syrup, so the ratio is low for the sugars. Most of the people around here determine sugar content with specific gravity hydrometer tests. In a lab we could use measured amounts and then systematically heat the material. We could also burn the material for caloric tests. But we don't care about that right now.
The way it is processed is fun, The sap is gathered into tanks. An "arch" is used for water removal, we use a small arch and it is fired with wood. that means we put wood into a fire all day while boiling 100's of gallons of water out of the sap.
As the process moves on, the arch becomes a thermal hydraulic system. Cool thin sap enters on the far side of a "back pan" and this pan cooks out a lot of water fast, as it enters it pushes warmer sap forward, and this becomes heavier, and maybe a bit hotter. Later after flowing through a maze of channels designed to boil the material fast, it enters a "front pan" where it boils further. Here the sap is hotter, and flowing from a "cooler" side to the side of the arch we "draw" out syrup. While this cooking material travels through a maze of compartments, a very hot fire is under this "pan" the sap is forming into syrup, it becomes heavier, thicker and also sweeter. when the water is boiled out the specific gravity changes, and also the temperatures. Water boils at 212 degrees, a "sugar" thermometer starts at 212, and I can draw syrup at a reading of 10 or 222 degrees F.
The sap moves around and thickens, it will collect in the last compartment, as cooler sap keeps flowing into the other side. At the last compartment the sap is almost cooked into syrup, and here is where close attention is drawn. Like any sugar, maple syrup will cook further very quickly into a fuel. Sugar fires are horrible, the material is sticky and rapidly rises in temperatures and also burns fast, this can quickly destroy the material and also the equipment. When this sap is in the last compartment and more sap is travelling towards it, the material cooks out more water. It takes a while for enough of this to move into the last compartment and shed water out to thicken it. I use thermometer readings to judge if it is ready, and check it with a hydrometer, I have almost always been rewarded by the thermometer. As water leaves this material it gets hotter, and at a specific temperature it is syrup, If it gets hotter still it becomes candy, then a fire.
Heating any sugar is dangerous, and burns are the number one concern. It is fun to use these pieces of equipment and realize the physics behind the operation. I am happy to have the opertunity to do this, because I love to eat sweets!
Take care!