You may have seen the Maple leaf in the center of the Canadian flag. The sugar maple's leaf has come to symbolize Canada. More than 80 percent of the world's maple syrup is produced in Canada. North America’s indigenous peoples were the first groups known to have produced maple syrup and maple sugar, well before the Europeans arrived. Aboriginal tribes developed rituals around sugar ­making. They celebrated the Sugar Moon (the first full moon of spring) with a Maple Dance. The Algonquians recognized maple sap as a source of energy and nutrition. Maple syrup production methods remain basically unchanged since colonial days, but have been streamlined. Maple syrup is made from the sap of sugar maple, red maple, or black maple trees, although it can also be made from other maple species. In cold climates, maple trees store starch in their trunks and roots before the winter. In the spring, the starch is then converted to sugar that rises in the sap. During the day, starch stored in the roots for the winter rises through the trunk as sugary sap, allowing it to be tapped. Sap is not tapped at night because the temperature drop slows the sap flow, although most taps are left in place overnight. The average maple tree will produce 35 to 50 litres (9.2 to 13.2 US gal) of sap per season, up to 12 litres (3.2 US gal) per day. Seasons last for four to eight weeks, depending on the weather. At 30 to 40 years of age, the trees are tapped. Maples can continue to be tapped for sap until they are over 100 years old. Maple syrup is made by boiling between 20 and 50 volumes of sap (depending on its concentration) over an open fire until 1 volume of syrup is obtained, usually at a temperature 4.1 °C (7.4 °F) over the boiling point of water. Syrup can be boiled entirely over one heat source or can be drawn off into smaller batches and boiled at a more controlled temperature. Boiling the syrup is a tightly controlled process, which ensures appropriate sugar content. The syrup is then filtered. The filtered syrup is packaged while still hot. The syrup can also be heated longer and further processed to create a variety of other maple products, including maple sugar, maple butter, and maple candy. A maple syrup production farm is called a "sugarbush" or "sugarwood". Sap is often boiled in a "sugar house" (also known as a "sugar shack," "sugar shanty," or cabane à sucre), a building louvered at the top to vent the steam from the boiling sap.