NORTHBROOK – It may still look and feel like winter on the North Shore, but deep in the woods of Northbrook’s River Trail Nature Center, part of Cook County’s large network of forest preserves, there’s one sure sign of spring.
Inside the Nature Center, a grove of centuries-old sugar maple trees – awake from their winter dormancy – are oozing out sweet, sugary sap through taps that drip into hanging silver buckets.
Early spring’s blend of colder night temperatures (20F) followed by warmer days (35-40F) make it ideal “sugar weather,” said River Trail’s assistant director, Brian Winters.
“Dripping sap always signals the changing of seasons,” said Winters. “The alternating cycle of freezing and thawing draws water from the soil into the sugar maple tree, creating increased pressure. When all that space is taken up, sap leaks out.”
If Northbrook were in Vermont, or the Canadian province of Quebec, the clear, watery sap would be boiled down into the sweet, amber colored syrup Americans love to pour over their morning stack of pancakes. In these northern regions, where the sugar maple tree species thrives and maple syrup is mass-produced, sugar weather kicks off in early April and ends in May.
But at River Trail, where sugar weather begins in mid-February and ends before the first of April, this small, isolated “sugar bush” is used to educate local school children, scout troops and visiting families about the science and biomechanics of trees.
Every weekend during River Trail’s sugar season, the forest preserve’s team of naturalists lead a series of public programs called “Sap’s Rising.”
“We tap a tree, hang a bucket and wait to see what happens,” said Winters.
According to Winters, who teaches groups of school children ranging from preschool to middle school, sugar maple trees like those found in at River Trail thrived in the Midwest 6,000 plus years ago, when a colder, wetter climate prevailed. As the climate gradually became warmer and drier, forests gave way to prairies. Sugar maples soon lost out to a more dominant, prairie-fire resistant tree species: the mighty oak.
As luck would have it, River Trail’s approximately 900-acre forest preserve is located on high ground, adjacent to the Des Plaines River, creating a natural firebreak and insulating this small sugar maple grove from fires that raged in the surrounding prairie.
“This grove is actually a remnant, left over from an earlier climatic period,” explained Winters. “It’s an accident of topography.”
In addition to weekly programs led by River Trail’s team of naturalists, the center holds an annual Maple Syrup Festival every March, attended by thousands of local residents. It’s a celebration of spring that includes guided walks and maple-syrup making demonstrations in River Trail’s own on-site Sugar Shack, a small wooden structure similar to those constructed by syrup makers hundreds of years ago.
Winters and his team demonstrate historic maple syrup making methods used by 19th century settlers and trappers and contrast them with modern, machine techniques.
Sugar maple sap, explained Winters, is actually 97% water and only 3% sugar. Boiling the clear liquid down, either in the hollow logs and metal cauldrons, used by early settlers, or in the large vats engineered by commercial maple syrup manufacturers, concentrates the sugar, thickens the liquid, and turns it a rich, golden brown. It takes 40 gallons of sap to create one gallon of syrup.
Before the advent of canning and refrigeration, maple syrup was usually boiled down to its granulated form and eaten solid.
“For early settlers, sugar was not just a treat, it was survival” said Winters. “By the beginning of spring, their food supplies were dangerously low.”
Today, regulations stipulate that genuine Canadian maple syrup must have a sugar content of at least 66%; 67% if produced in Vermont.
And not every sugar maple tree can make large quantities of sap. Only trees roughly 80 years or older are mature enough for syrup making.
“When you see a tree that’s 14’’ or more in diameter, that’s a tapping tree,” said Winters.
River Trail Nature Center, 3120 Milwaukee Avenue, Northbrook, www.fpdcc.com.