The mystery of syrup color

Most of you probably know that maple syrup comes in different colors, or grades.

You may also know that the syrup color changes as the sugaring season progresses: Lighter syrup is usually made when the sap first begins to flow; darker syrup shows up later.

Darker syrup has a stronger flavor than the lighter syrup, but the quality and sugar content is the same. (This is why, in 2014, Vermont changed the grading names. The USDA adopted them a year later). It’s just a matter of taste preference.

But why does early sap make lighter syrup than late-season sap?

We asked Marshall Webb, who’s been sugaring at the Farm for many years.

“The color of the syrup is determined by two factors: tree physiology and microbes,” he said.

Tree physiology:

As a tree prepares to produce leaves, it converts starch stored in its trunks and roots to sugar, then draws moisture from the ground to help carry those sugars to its branches. As the season warms and its leaf buds swell, the chemistry of the sap changes. By late March or early April in the Champlain Valley, the sap actually gets “smelly and gooey,” according to Marshall.

But it turns out, microbes are really where it’s at.


Fresh sugar maple sap is about 2% sucrose; the rest is water. On its way to the sugarhouse, sap picks up microbes that break some of that sucrose down into two simpler sugars: fructose and glucose. (This also happens if the sap sits around in the tank for a while.)

As temperatures warm up over the course of the sugaring season, more microbes tend to show up in the sap, producing more of these simple sugars.

Here’s where it gets interesting. While the sap is being cooked in the evaporator (killing all those microbes!), “nonenzymatic browning reactions” occur that affect syrup color and flavor. It turns out that fructose and glucose get involved in these reactions more than the sucrose, which is more stable.

So more microbes = more simple sugars = darker, more flavorful syrup late in the season!

There’s a great article in Northern Woodlands magazine about all this if you want to know more (it’s where I got most of this information).

But mysteries remain. Case in point: Last year, we made primarily dark syrup, along with some amber. This year, we’ve been sugaring for more than a week and have made over 300 gallons of golden syrup!

When asked about it, Marshall just shrugs and smiles.

So there’s a lot of mystery still to unravel in this deceptively simple business of boiling sap into syrup.

Posted by Holly Brough

March 21, 2020


I used to do backyard sugaring at my home in Shelburne. One year I had a pint of fully boiled almost colorless syrup-very light golden. It was from early in the season, as I recall. If it had been in the days of cell phones I would have a picture of it.
We make 50 gals. of syrup each year, most of it grade A fancy from the first third of the season. The later, dark syrup we use for cooking. The taste of the early syrup is much more refined and far better tasting on pancakes and waffles. The later syrup is better in baked beans or oatmeal. All of it is good but early is much better.
Hi. Very first time trying this. I tapped five trees and got about 250 Liters of sap. Boiled down I ended up with around 4 Liters of syrup. Very light in color and tastes amazing. A friend gave me a half Liter that is very dark. I think I will keep the dark for baking.

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