Maple syrup is a syrup usually made from the xylem sap of sugar maple, red maple, or black maple trees, although it can also be made from other maple species. In cold climates, these trees store starch in their trunks and roots before the winter; the starch is then converted to sugar that rises in the sap in late winter and early spring. Maple trees can be tapped by drilling holes into their trunks and collecting the exuded sap, which is processed by heating to evaporate much of the water, leaving the concentrated syrup.Maple syrup was first collected and used by the indigenous peoples of North America, and the practice was adopted by European settlers, who gradually refined production methods. Technological improvements in the 1970s further refined syrup processing. The Canadian province of Quebec is by far the largest producer, responsible for 75% of the world's output; Canadian exports of maple syrup in 2014 were C$ 380 million (approximately US$ 300 million), with Quebec accounting for 85% of this total. Vermont is the largest producer in the United States, generating about 6% of the global supply. Maple syrup is graded according to the Canada, United States, or Vermont scales based on its density and translucency. Sucrose is the most prevalent sugar in maple syrup. In Canada, syrups must be made exclusively from maple sap to qualify as maple syrup and must also be at least 66 percent sugar. In the United States, a syrup must be made almost entirely from maple sap to be labelled as "maple", though states such as Vermont and New York have more restrictive definitions (see below). Maple syrup is often eaten with pancakes, waffles, French toast, oatmeal or porridge. It is also used as an ingredient in baking, and as a sweetener or flavouring agent. Culinary experts have praised its unique flavour, although the chemistry responsible is not fully understood.