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Aaron Wightman

March 11, 2019

The Science of Maple Syrup: From Tree to Pancake Stack and Everything in Between

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Twenty miles southwest of Cornell’s Ithaca campus grows a forest of sweet trees. The tubing at their trunks carry sugary sap awaiting to be transformed into a crowd-pleasing breakfast staple: maple syrup.

In the Arnot forest, a 6000 tree-section is an integral part of the Cornell Maple Program. But how do you get from sap to syrup? Aaron Wightman, the extension associate at the Cornell Maple program highlights the food science behind the maple syrup making process.

This time of year –– late winter to early spring –– is prime for maple syrup production, especially in New York, the second largest producer of maple syrup.

“The trees store their energy in the form of starch for their dormant period in the winter, but as winter moves closer to spring, the trees start releasing enzymes,” Wightman said, including “the same enzyme that you have in your mouth to help dissolve starch: amylase.”

Once amylase is coursing through the tree, it converts the stored starch to sucrose. But, according to Wightman, that sucrose sap cannot flow without the freezing and thawing that happens between the cold nights and warmer days during this winter-spring limbo.

“When it warms up, the CO2 inside the stem expands and creates positive pressure, so when you drill a hole in the tree, the sap is going to get squeezed out,” Wightman said.

Wightman also explained that the freezing causes the opposite process. The cold temperatures cause the gas inside the stems to contract, creating a vacuum that sucks more water up into the tree.

Arnot Sugarhouse where sugar is processed

Aaron Wightman

Arnot Sugarhouse where sugar is processed

Once the producers have this slightly sweet sap, they need to concentrate the sugar. To do this more efficiently, some sugarmakers utilize reverse osmosis. Wightman explained that the Arnot Forest’s reverse osmosis machine has a membrane with holes small enough to allow water through, but not larger sugar molecules. Under pressure, this separates the water and sugar, and concentrates the sugar in the sap, turning a 2 percent sugar solution to a 20 percent solution.

However, for the product to be legally called “maple syrup,” it needs to reach the magic concentration of 66 percent sugar. To achieve this, the sugarmakers boil the sap, which further concentrates the sugar solution and also introduces the classic maple flavors and caramel colors.

Evaporator in Arnot Sugarhouse boils the sap

Aaron Wightman

Evaporator in Arnot Sugarhouse boils the sap

According to Wightman, the color is what determines the four different grades of maple syrup, from golden to very dark amber. The color depends on the types of sugars inside the syrup and the timing of the season when it was collected.

“The only sugar that comes out of a maple tree is sucrose, and sucrose has a pretty high caramelization temperature,” Wightman said. “But as it passes through the collection system, yeast and bacteria will break down some of that sucrose into glucose and fructose.”

He explained that as the sugaring season gets longer, more bacteria and yeast from the air are introduced to the sap through the tubing, making more fructose and a darker syrup. Fructose has a low caramelization temperature at 110˚C (compared to sucrose’s 160˚C) and therefore acquires a dark tint when cooked.

Steam from Arnot Sugarhouse

Aaron Wightman

Steam from Arnot Sugarhouse

Lately, changes in the length of syrup season suggest that climate change may be impacting maple syrup production.

“Back when I first started making syrup as a child in the 1970’s, we didn’t tap our trees until March. Now a lot of big producers will tap their trees before Christmas. We’re seeing more of those freeze-thaw cycles earlier in the winter,” Wightman said.

Though this may not seem like a problem, the earlier start means the trees are being tapped for a longer duration of time. This poses technical challenges, according to Wightman.

“When you tap a tree, it actually starts to slowly lose productivity over time. The main reason is bacteria and yeast get sucked back into the tree … and that makes the tap hole dry out more quickly.” Wightman said.

To help prevent this contamination and drying out, the Cornell Maple Program is developing new tubing systems. According to Wightman, one gadget is a check valve that allows sap to flow out of the tree, but closes when the tree tries to suck sap back in. Another technology solution is tubing with ionic silver that sanitizes sap that passes back through the spout to the tree.

Despite these challenges, the maple industry continues to boom. A recent grant from the USDA is making it possible for the Cornell Maple Program to continue research, provide expertise on production and improve sustainability on sugarbush management.

The Cornell Maple Program also has plans to create a new sugar house facility and a new line of research in other maple products including maple kombucha, maple wine, maple vinegar and even maple soda.

Maple wine research at Arnot Forest

Maple wine research at Arnot Forest

And, if you are ready to try out some maple products or just love the classic maple syrup on pancakes, keep an eye out for Cayuga Nature Center’s Maple Fest on March 17.