You may know maple syrup as your favorite topping for pancakes, but do you know how it got from a maple tree to your plate? Maple syrup is a sweet treat made possible by science, and Minnesota is one of the only places in the world that can make it! Learn all about this springtime tradition.
Three Rivers Syruping in the News
The Science of Syruping
The science of syruping begins in the summer when sugar maple trees, covered in leaves, make sugar through photosynthesis. The sugar is transported through the trees' phloem, helping them grow taller and wider.
As fall approaches and the days become shorter, the trees stop consuming the sugar and start storing it in their roots as energy for next spring. When the leaves fall off the trees and they go dormant, it is possible to collect sap from them.
Freezing and Thawing
To collect syrup, conditions have to be just right: above freezing during the day and below freezing at night. The most reliable time for this weather is the spring.
When these conditions arrive, we can start to tap maple trees. We tap into the xylem layer of the tree, which is the part that carries water from the tree's roots to its leaves.
How Does Xylem Work?
In all trees, the xylem is made of long, skinny cells called fiber cells, and short, tube-shaped cells called vessels. In maple trees (unlike most other trees), the vessels are filled with water and the fibers are filled with gas.
The xylem acts like a bunch of drinking straws. In the summer, the leaves suck water up through the straws. In the winter, there are no leaves to suck the water up, so the sap doesn't move up the xylem as easily.
What Happens to the Xylem in Spring?
When the temperature drops below freezing at night, the water in the xylem's vessels freezes and expands, squeezing the gas-filled fiber cells. At the same time, the air in the fiber cells shrinks. This combination creates a suction that pulls water up from the roots at night.
When temperatures warm up during the day, the gas in the fiber cells expands, pushing on the water-filled vessels. This creates a lot of pressure in the tree — so much that the trunk will expand during the day in spring!
How Does This Help Us Collect Sap?
This pressure is what allows us to collect sap. When we drill a hole in the tree, the pressure forces the sap out of the hole and into the bucket or bag we've placed below our tap.
We can continue to collect sap as long as we have these freezing and thawing conditions. Once buds appear on the tree, it's usually time to stop.
The History of Maple Syrup
Starting the Syruping Tradition
The history of maple syrup begins with the Indigenous groups who invented it. At the first signs of spring, tribes would make their way to the sugarbush (maple tree forest) to tap maple trees.
They used axes to cut V-shaped slashes into the trees. In the slashes, they inserted birch bark that acted as a ramp, sending the flowing sap into makuks, bowls made of birch bark.
Turning Sap to Sugar
Tribes allowed the collected sap to freeze and thaw several times. They threw away the ice that formed, knowing it was only water because the sugar in the sap wouldn't freeze. This freezing process meant less cooking time.
Next, they cooked the sap in makuks over a fire. The birch bark wouldn't burn unless the sap got too low. It's likely they placed the cooked-down syrup into a hollow log with heated rocks that helped bring it to a boil.
Indigenous groups continued to cook the syrup down until it became sugar. Sugar is much lighter to carry, not as messy if spilled, and doesn't spoil like syrup. Some tribes also cooked syrup into a taffy, which was used as an energy food while traveling.
Syrup Becomes Popular During and After WWII
Indigenous groups taught European settlers how to make maple syrup, but it didn't become popular in Minnesota until World War II and after, when sugar rations were put in place, forcing people to find other sugar sources.
From Sap to Syrup
Sap from sugar maple trees is made up of about 2% sugar and 98% water. In order to increase the sweetness and turn it into syrup, some of the water content has to be removed. You can do this using the freezing method that Indigenous peoples used, or you can boil the sap from the beginning.
The longer sap is cooked, the more sugar will be in the final product. When the syrup is done cooking, it should be about 67% sugar. Darker syrups have a higher sugar content and stronger flavor than lighter syrups.
Fun Fact: It takes about 40 gallons of sap from a sugar maple tree to make one gallon of maple syrup!