Salem Maritime National Historic Site
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    The three main phases of matter are solid phase, liquid phase, and gaseous phase.

    • Evaporation: the transition of matter from liquid phase to gaseous phase.
    • Sublimation: the transition of matter from solid phase to gaseous phase.

    Audio Transcript

    Humans aren’t the only ones who enjoy the generous gifts of the sugar maple tree. Just like us, squirrels tap maple trees, puncturing the bark with their sharp teeth, leaving small open grooves on the sugar maple trunk or vertical slanting branches. Here, sugar-rich, watery sap slowly trickles out, sticking to the bark and spreading down the tree. But squirrels know that good things come to those who wait. 

    As sap drips and spreads down the sugar maple trunk, sunlight warms its surface and water evaporates. Nighttime brings freezing temperatures again. The sticky maple sap hardens, and more water molecules are removed in a process known as sublimation. What is left is crystallized sap, with a high concentration of sugar, full of carbohydrates, a sort of maple sugar rock candy.  

    Squirrels return to their taps on the sugar maple tree early the next morning, before the sun is high and the sap begins flowing again. By this time of year, it’s late winter or early spring, and squirrels’ food caches are nearly empty. The maple sap, full of carbohydrates, comes at the perfect time, just the thing needed to keep squirrels warm through the last freezing nights.  

    In her 2013 book, Braiding Sweetgrass, a professor, scientist, and member of the Citizen Potawatomi Nation, Robin Wall Kimmerer, describes Indigenous people of the Maple Nation, who “collected sap [from the sugar maple tree] in birch bark pails and poured it into log troughs.” They left maple sap in these long, narrow, open containers overnight to freeze, removing sheets of ice in the morning. The process left behind a concentrated solution, which was boiled and further concentrated through the process of evaporation.  

    "The freezing nights did the work of many cords of firewood, a reminder of the elegant connections: maple sap runs at the one time of year when this method is possible,” Kimmerer writes. “It is said that our people learned to make sugar from the squirrels” (67).