University of Vermont
Department of Plant and Soil Science

Spring News Article


Dr. Leonard Perry, Horticulture Professor
University of Vermont

Many know that maple syrup comes from the sap of the sugar maple tree, collected and boiled down each spring to make it denser.  In fact, native Americans were making it when the first European colonists arrived.  Whether you make your own maple syrup as a fun family activity, for income, or just enjoy using it, you should know some of the interesting facts about this important agricultural product in our region.

The Cornell University maple research and education website ( has many interesting facts about maple syrup, including the one that it takes 43 gallons of sap (with 2 percent sugar content) boiled down to make a gallon of maple syrup.  Since sugar content of the sap can vary by tree, and previous season growing conditions, this can range from 40 to 50 gallons or more for a gallon of syrup. On average, sugar content of sap is about 2.5 percent.  If the tree is too vigorous, it may use up more sugars and so result in less sweet sap.  Or if the tree is attacked by pests, or grows poorly, it may produce fewer sugars.

A tree in the forest with gravity lines or buckets may produce 10 to 14 gallons of sap in the spring, while roadside trees (or those in a maple stand with vacuum tubing) may produce 15 to 20 gallons.  So, in a good season, it would take at least two roadside trees to produce enough sap for about a gallon of syrup.  The amount of sap will vary with the tree, weather, length of the sap season, and method of collecting the sap.

The maple syrup we find in containers begins its life as sugar in the leaves of maples, produced by the process of photosynthesis.   The sugars are transported into the wood for winter storage in the form of carbohydrates.  In spring they are converted to sucrose and dissolved in the sap to flow through the tree.

Sugarmakers drill holes in sugar maple trees each spring, just under a half inch wide and about two to three inches deep, at an upward angle.  Bits are inserted on which to hang buckets or similar containers (home sugarmakers may use plastic containers), or to insert the colorful plastic tubing one sees crisscrossing maple stands in spring.

To avoid stressing trees, only those 10 inches or more across should be tapped.  This is measured at a standard four and one half feet above the ground (which may be seen as DBH or diameter at breast height). A tree 10 to 17 inches wide should have one tap, one 18 to 24 inches two taps, and one larger across three taps.  Proper tapping of sugar maples should cause no injury or stress to them, and they may remain productive for 100 years or more.

With warm temperatures above freezing in spring, pressure develops in the tree and causes the sap to flow out these openings or taps.  Then, with colder temperatures below freezing, suction within the tree pulls in more water to make more sap. When the fluctuations in temperature lessen, the sap stops flowing. This period of sap flow usually falls within early March to mid April, depending on the season.

The sap is boiled to evaporate water and concentrate the sugar.  The end product will boil at about 219 degrees, seven degrees above the boiling point of the sap.  This can be checked with a candy thermometer.  The top quality syrup will contain no less than 66 percent sugar (measured as “Brix”). 

When buying maple syrup you will be confronted with some choices in grades, all based on U.S.D.A color standards but with words that may vary with region.  Generally the darker amber the color, the stronger the maple flavor.  Make sure when buying maple syrup to read the label to make sure it is pure, if that is what you are seeking, and of the flavor you desire. Contrary to some claims you may hear about better syrup from one region or state, quality of syrup will be affected instead by the season’s weather, time of season the sap is collected, and how it is processed.
What may vary with the location or “provenance” are the many other flavor components in maple syrup.  Around 300 different compounds have been identified, not all being present in the same syrup.  In addition to the maple flavor in all syrups, there may be caramel, vanilla, nutty, buttery, honey, chocolate, or coffee flavors detectable. 

Why the sugar maple has sweeter sap with better flavor than other maples is not really known.  The reason may lie in the structure of the wood where the sap is stored.  If sap is collected once buds develop on the trees, it becomes less pleasing.  The sugar maple has the longest period before buds develop, so the longest season to collect sap among the maples. 

The sugar maple primarily grows in the northeastern United States and eastern Canada, so this is where maple syrup is produced.  A less sweet syrup with different flavor is made in Alaska and Siberia from the sap of birch trees.  Another species of maple is tapped in Korea, but only to drink the sap. 

Once you have maple syrup in a properly filled and sealed container, it can last up to a year, or up to six months in the refrigerator if opened.  When cooking, use maple sugar similar to white sugar.  There is no evidence it is healthier except that, being unrefined, it may contain compounds with some health benefits.  If using maple syrup in cooking, you can use one cup instead of one cup white sugar.  Reduce the liquid in recipes, though, by 3 Tablespoons for each cup of syrup used. 

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