The collection of maple sap and its conversion to syrup or sugar illustrates many chemical principles, such as osmotic pressure and colligative properties.

The driving force behind the flow of maple sap is by no means obvious.  The calculated osmotic pressure of sap, a 2% by weight solution (0.059M) of sucrose, is approximately 1.3 atm at 273 K or 1.4 atm at 298 K.  This is sufficient to push water to a height of about 45 feet, but many maple trees are taller than that.  Besides, a maple tree continues to bleed sap for several days after it has been cut down.

The production of maple syrup involves concepts such as osmotic pressure, solubility, and colligative properties. (V. Holtgrewe)

An alternative theory suggests that sap is forced out of the tree by bubbles of gaseous carbon dioxide, produced by respiration.  When the temperature drops at night, the carbon dioxide goes into solution, and the flow of sap ceases.  This would explain the high sensitivity of the sap flow to temperature; the aqueous solubility of carbon dioxide doubles when the temperature falls by 15 °C.

When making maple syrup, it takes 20 to 40L of sap to yield one liter of maple syrup.    To remove the water from the sap you could directly boil it off or you could first freeze the sap, as the colonists did 200 years ago.  The ice that forms is pure water; by discarding it, you increase the concentration of sugar in the remaining solution.  The remainder must be boiled off.   The characteristic flavor of maple syrup is caused by compounds formed upon heating, such as acetol, cyclotene, and vanillin.

When the concentration of sugar reaches 66% by weight, you are at the maple syrup stage.   The calculated boiling point elevation at this point (660 g of sugar, 340 g of water) is 3.0 °C, somewhat less than the observed value, about 4 °C.  The temperature rises very rapidly around 104 °C, which makes thermometry the method of choice for detecting the "end point."

Masterton/Hurley:  Chemistry Principles and Reactions,  3/e,  pp. 293–294