Early methods of sap production demonstrate a technology that made efficient and creative use of the materials of the day. Since metals were not available, a folded piece of birch bark acted as a spile and birch bark containers collected the sap that dripped from the spile. The lack of metal also makes the task of producing syrup more difficult. This was overcome by using containers made from the heat-resistant inner birch bark rather than the very flammable outer bark and by dropping red hot stones into the sap to speed the evaporation of water from the solution. The process of reducing syrup to sap provides students with an opportunity to observe the relationship between heat, temperature and the state of matter.
Students sometimes use the terms heat and temperature to describe the same thing.
Temperature should be clarified as a measure of the amount of heat energy that is absorbed by the sap. The sap, in turn, radiates an increased amount of heat shown by its elevated temperature. The temperature of the sap continues to rise until it begins to boil. At this point, the energy absorbed by the sap is causing the water within the sap solution to change states from liquid to vapour. If enough water is driven off and die solution is concentrated, when the heat source is removed and the sap loses energy and cools, students will observe the liquid beginning to crystallize and form a solid.