When temperatures begin to rise in February and March, maple sap begins to flow from the roots of trees up the trunks to the branches and limbs. During the short period of spring when the daytime temperatures are above freezing, and the night temperatures are below freezing, the sap flows up and down the tree trunks daily.
Appalachia has a long history of sugar making. The Cherokees threw hot rocks into hollowed-out logs that were filled with sap. The early colonial settlers, too, quickly learned to make the sweet stuff: even though census enumerators were inconsistent in reporting maple sugar production, the 1790 output is reported for 26 Appalachian counties of southwest Virginia, West Virginia, east Kentucky, and east Tennessee.
While all maples produce the sweet sap that eventually may become syrup, it is only the sugar maple and black maple that are generally tapped. At least 75 percent of all commercial maple sugar comes from sugar maple trees because they are the species with the highest sugar content in their sap (about 2%).
Sugar bush workers drill small holes in the trunks, and insert taps to allow some of the sweet sap to come out. At first these taps consisted of carved, hollowed out pieces of wood, with a wooden bucket hanging from them to collect the sap. Later, metal taps and buckets were mass produced, as well as bucket covers to keep the sap cleaner.
In the 1930s the sap was hauled to the sugar house by human, horse, ox, and tractor power. Considering that a sugarbush usually contains hundreds of trees, this was an incredible amount of work. Large trees can fill upwards of 10-12 buckets each.
Some folks think the sap just comes out of the trees and is packaged as syrup for sale. Wrong! It takes 40 gallons of sap to make one gallon of maple syrup. Even more is required to make maple sugar. The water content of the sap has to be boiled off, leaving the syrup behind. You can’t just leave the sap around and boil it at your convenience either! The sooner you boil the sap, the better the quality of the syrup. If you wait too long, the sap will spoil and you’ll have to dump it.
The sap is transported to a holding tank where it accumulates until there’s enough to boil off—known as “sugaring off.”
Sources: http://scholar.lib.vt.edu/faculty_archives/appalachian_women/frontier.htm; http://www.fs.fed.us/r8/spf/documents/southernhardwoodmanagement.pdf