From colonial times to the 20th century, sugar producers collected the sap by punching a small v-shaped gash in the maple tree, inserting a wooden or metal spout into the cambium, and hanging the bucket into which the sap dripped. This picturesque collection method has mostly given way to systems of plastic taps and tubing, which carry the sap from many trees to a central holding tank.
The flow of sap is triggered by a thaw following on a hard frost in the sunny days of late winter (February, March and April). Over a six-week season, the taps remove around 10% of a tree's sugar stores, in an average of 5 to 15 gallons per tree.
It takes around 40 parts of sap to make 1 part syrup. The sap contains around 2% sucrose at the beginning of the season, and only half that at the end; therefore, late-season sap must be boiled longer and has a darker and stronger flavor. Today, many procurers use energy-efficient reverse osmosis devices to remove about 75% of the sap water without heat, then boil the concentrated sap to develop its flavor and obtain the desired sugar concentration. They aim for a temperature around 7 degrees F above the boiling point of water, the equivalent of a syrup that's around 65% sugar. Maple syrup can be boiled down further to create maple sugar, which is approximately 90% sucrose.