[audio:http://wamcradio.org/EarthWise/wp-content/uploads/2013/03/EW-03-21-13-Maple-Syrup.mp3|titles=EW 03-21-13 Maple Syrup]
Several sugar maples on my property are currently outfitted with taps and buckets. Their sap is destined to sweeten future breakfasts. Maple sugaring, which dates back to the indigenous peoples of North America, is an elegant mix of biology, physics, and patience.
All trees produce sugars during the growing season. In the fall, these sugars are shunted to storage tissues. Some sugars travel from smaller branches down tree trunks in what are called rays cells. Rays hold the sugars that trees use for everything from building new cells to repairing woodpecker damage. They also give us sap.
Sugar maple sap has a high concentration of sucrose—which makes it sweet. It flows freely during the spring. You can tap other species, but you’ll work harder for your syrup. The sap-to-syrup ratio for a sugar maple is 40:1. For a birch, the ratio is 80:1.
What makes sap flow? The answer lies in physics. You need cold nights with temperatures near freezing, followed by sunny days with temperatures in the 40’s to 50’s. This freeze/thaw cycle causes a change in pressure, which forces the sap to run out of the tree and into the sap-collecting bucket.
Converting sap to syrup requires careful attention—undercooked syrup is watery while overcooked syrup can crystallize. Early sap usually produces light amber colored syrup, with syrup darkening as the season progresses. This is likely due to sugar concentrations, as early syrup has a high concentration of sucrose relative to other sugars.
When trees begin to tap on their sugars for their own growth, it heralds the end of the sugaring season. Sap flow decreases and it’s time to put the buckets away and start planning your garden.
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Photo, taken on February 21, 2010, courtesy of Peter MacDonald/MA Office of Travel and Tourism via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY, with partial support from the Field Day Foundation.