Why are maple trees tapped to make maple syrup?

Understanding the mechanism of sap flow helps explains why maple trees can be tapped to produce syrup. Maple sap contains sugars, amino acids and other compounds that create that unique maple syrup “taste” after the sap is boiled.

March is maple syrup season in many parts of Michigan. This is the time of year that sap “runs” in maple trees, meaning they can be tapped to draw off the sap and boil down into maple syrup. While sap does flow in tree species other than maples, there are few species that can be tapped to produce an edible food product similar to maple syrup. Michigan State University Extension explains why sap in maple trees can flow vigorously and what accounts for its unique “maple” flavor.

Sap flow in maple trees is generally the result of fluctuating temperatures coupled with positive and negative pressures that develop inside a dormant maple tree in response to early spring temperatures. When daytime temperatures rise above freezing a positive pressure develops inside a tree – forcing the sap upward from the roots toward the crown. If there are any holes or openings in the tree that connect to the sapwood (e.g. tapholes, broken branch stubs, frost cracks, etc). – sap will push itself out.

If nighttime temperatures drop below freezing that positive pressure ceases and is replaced by a negative pressure, or suction, inside the tree. This allows tree roots to absorb water from the soil. In essence, this replenishes what was lost. Then, when temperatures again rise above freezing a positive pressure resumes and sap flows out of the tree.

But this only explains why sap flows and not really why maple sap has a sweet taste. On average, maple sap extracted from sugar maple trees is about 2- 2.5 percent sap sugar content and is the result of the photosynthesis and carbohydrate production from the previous growing season. In addition to its sweetness, maple sap has certain amino acids and other compounds that provide that unique maple syrup taste – once it is boiled down and finished.

Maple sap as it exits a maple tree is a clear, watery substance with only a trace of sweetness. That’s why it requires on average about 43 gallons of sap to produce one gallon of finished maple syrup. Over the course of a season, one tap hole can produce between 10-15 gallons of sap on average.

To make maple syrup from sap, it must be boiled down over a long period of time to evaporate the water and concentrate both the sugar content and the unique flavor compounds that result in finished maple syrup.

The best types of maple trees to tap are the sugar maple and its cousin the black maple. These species often produce the sweetest sap. However, red maple and, to a lesser degree, silver maple can also be tapped. There sap, however, is usually less sweet and produces more “sugar sand” during the boiling process. The only maple that should not be tapped is the Norway maple as its sap is milky and not clear.

Maple syrup is only one of many different types of natural resource enterprises produced in Michigan. For more information on Michigan maple syrup, contact the Michigan Maple Syrup Association or the MSU Extension Bookstore where an inexpensive publication on making homemade maple syrup can be purchased.

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