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Sugar Content

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Checking sugar content with a hand-held refractometer in a Vermont sugarbush. Photo by Dave Mance III.

On the back of maple syrup cans, and in public relations pamphlets designed to explain to consumers why maple syrup is so expensive, the ratio of 40 gallons of sap to 1 gallon of syrup is often used to say: “Look how much work this is!” Truth be told, that number is always in flux, and 40 to 1 is often an under-exaggeration.

The 40 to 1 ratio is based on C. H. Jones’s “rule of 86,” a simple equation (based on some pretty complicated calculations), which holds that a tree’s sugar content percentage, divided into 86, will give you the number of gallons of sap needed to produce a gallon of syrup. If you have 1 percent sap, it takes 86 gallons to produce a gallon of syrup; at two percent it takes 43 gallons. And so forth.

It all begs the question: what determines a tree’s sugar content?

For starters, sugar content in all trees is in flux throughout a sap season. It follows an arc. As a tree shakes off its winter dormancy, sugar content may hover around 1 percent. The tree is logy, and there’s not a lot of metabolic activity going on. At the height of the season, when the tree’s warmed up and is efficiently converting starch to sugar, the sugar content in a mature tree should be up around 2.5 percent. At the end of the season, though, as the tree depletes its starch reserves, the sugar content plummets again.

Trees also vary in sugar content from year to year. Bad growing summers mean depleted starch reserves the following winter, which can translate into lower spring sugar content. In other words, if forest tent caterpillars defoliate a maple tree in the summer, or there’s a bad drought, a sugarmaker can assume that the following spring’s sap will be less sweet than normal.

Also playing a role are a tree’s health and where the tree grows. If you tap a sprawling yard-maple with a big ol’ regal crown, it’s going to yield dramatically sweeter sap than a woods tree with a small crown. The yard maple doesn’t have to compete with any neighbors for nutrients and light, which means a bigger crown, more leaves, more photosynthesis, more starch, and more sugar.

Finally, and perhaps most interestingly, tree genetics play a role in sugar content. Like brown-eyed children of brown-eyed parents, little maples can inherit sweet or not-so-sweet sugar genes from their parents. Scientists in New England, New York, and Ohio started studying super-sweet maples in the 1950s. They identified sweet trees and cloned them. Today, the progeny of these super sweet trees average six-to-seven percent sugar in a season, with some incidences of 10 or even 12 percent reported.

Cornell University sells super-sweet seedlings to sugarmakers who have the patience and foresight to want to plant maple orchards. According to Professor Brian Chabot, Cornell still has some seedlings for sale, but in the future, seedlings will be distributed through a private nursery.

The take-away from all this is that some maple trees are sweeter than others. How this information applies to a sugarmaker’s forest-management practices may depend on the scale of the operation. A large-scale producer may be less concerned about the sweetness of an individual tree because they’re already concentrating sap through reverse osmosis or steam-away technology. But to a smaller producer, knowing the sugar content of one tree versus another can make a huge difference in efficiency and production.

For this reason, when you’re thinning your sugarbush, it behooves you to check your maple trees before you mistakenly cull out a super-sweet tree. The best way to do this is with a hand-held refractometer. Any time the sap’s running, you can poke a tiny hole into a tree and gather a drop of sap. Check the sweetness and note how a tree compares to its similarly sized neighbors. Flag sweet trees and spare them from the axe.

You can buy a refractometer from any sugaring supply dealer (it should cost you between $50 and $100). Some county foresters also have them available to borrow. Most refractometers are self-calibrating, so upkeep is no big deal.

One final note: if you’re a beginning sugarmaker and you find yourself scratching your head trying to reconcile your 1.5 average against the old timer down the road who’s claiming to be boiling 4 percent sap, know that he’s probably lying. Sugar content “fish stories” are the norm in this industry, and I’m no exception to the rule.

Just last year, a visiting sugarmaker called me on one such exaggeration; when we tested the tank of sap in question, we found I’d unintentionally overestimated the sugar content by a full percentage point. While pondering the roots of my fib, we eventually decided that sugarmakers, like farmers in general, are born optimists – you sort of have to be in this business. Afterwards, sensing that an already long night of boiling had just grown twice as long, this visitor was gracious enough to help me load the firewood cart.

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