The Science of Syrup

Illustration by Adelaide Tyrol

In maple country, it seems like everyone has a favorite syrup grade. Mine is U.S. Grade A dark amber. But soon, I’ll have to figure out how my favorite grade of the past jibes with a new system that several Northeastern states plan to adopt in the next few years, and that other states – as well as Canada – are also considering.

It turns out that, at least in New York, Vermont, and Maine, my favorite amber will soon be called either Grade A Amber, Rich Taste or Grade A Dark, Robust Taste, depending on which end of the amber spectrum I prefer. Lighter syrups tend to have more delicate flavors, while darker ones are more intense – a relationship on which the old maple syrup labels, that described color only, relied.

So why doesn’t all syrup taste the same? Sugars in maple sap undergo a series of changes during collection and processing that influence both color and flavor. “The most important determinant of what flavor develops in syrup are the reactions that occur when heat is applied as we process sap into syrup in the evaporator,” explained Abby van den Berg, a researcher at the Proctor Maple Research Center at the University of Vermont.

Sugar maple sap fresh from the tree is roughly 98 percent water. The rest is dominated by sucrose. As the sap drips into the tube, bucket or bag, it picks up microbes. The microbes, including bacteria and yeast, break the sucrose molecule in two. This process is called inversion, and the sugars it produces – fructose and glucose – are called invert sugars.

The microbes break sucrose up because invert sugars are easier for them to digest. As the sugaring season progresses, there’s a tendency for more microbes to be present in sap and break more and more of the sucrose into invert sugars.

Amino acids in maple sap increase over the season as well. Researchers believe this increase is due to metabolic changes within the trees as they leave winter dormancy and prepare for the growing season.

When maple sap is processed, it is usually piped into an evaporator divided into several compartments. Sap entering the evaporator is made up of about two percent sugar. As the sap passes through each heated compartment, water evaporates, concentrating the sap into syrup (and killing those microbes). By the time the product is piped out of the evaporator, it is approximately 67 percent sugar.

While the sap is being cooked in the evaporator, critical chemical reactions occur that affect syrup color and flavor. Most of those are nonenzymatic browning reactions, a broad term for reactions that result in color and flavor development in food. Sugars play a key role.

“Sucrose is not as reactive as its two component parts,” said van den Berg. “So generally, the more invert sugars you have in your sap, the greater the level of those nonenzymatic browning reactions.” The more nonenzymatic browning, the darker and more flavorful the syrup.

A Maillard reaction is a more specific term for browning; it involves the reactions  between invert sugars and amino acids (and other nitrogen-rich compounds) in food. “Much of what is yummy about toast has a lot to do with Maillard reactions that develop color and flavor in that toast,” explained van den Berg.

No surprise, then, that the yumminess of maple syrup also has to do with Maillard reactions. More fructose and glucose, plus more amino acids, equals more Maillard reactions and richer flavor. That’s why late-season syrups, which generally have greater microbial concentrations, have more intense colors and flavors.

But too much of a good thing – in this case, microbes – can create an unmarketable off- flavor. That’s why many maple syrup makers clean their equipment scrupulously.

These are just the basics; the more closely you study syrup flavor, the more complicated things become. Researchers have identified over 200 flavor compounds in syrup. Sugar degradation (the breakdown of sugars when heated) also plays a part, as do compounds produced by sugar maple trees as defenses against insects and injury.

“It’s very, very complex,” said van den Berg, “and we know quite little in the big picture.”

In any case, I know I like my dark amber – I mean Dark, Robust Taste.

Audrey Clark is a naturalist and writer who lives in Burlington, Vermont.

  1. Robert Eldredge
    Mar 26, 2014

    Need help on a question. My son in law believes that maple syrup that is not labeled organic comes from trees that have been fertilized and sprayed. True or not?

  2. Dave
    Mar 27, 2014

    Not true. When syrup is boiling in the evaporator, sugarmakers use a defoaming agent to keep the bubbles from getting too high. Organic producers use a certified organic canola oil. Conventional producers use regular canola oil, or a dairy-based product. That’s the only tangible difference between organic and conventional syrup. There’s been research done on fertilizing a sugarbush with calcium, but i’ve never seen this done outside of academia—it’s cost prohibitive. As is spraying, except in extreme cases. My family has been sugaring for 60 plus years and we’ve sprayed once, during a forest tent caterpillar outbreak. We used Bt, which is an organic pesticide. But again, this was a once-in-a-generation thing. Nobody sprays regularly; there’s no need.

  3. Mike
    Apr 04, 2014

    I’m a sugarmaker and I have to say that this is probably one of the best articles I’ve ever read on the span of a season relative to syrup color and taste.  It also helps explain a lot about how this season started in with darker syrup and is staying that way.  No Fancy here this year.  I noticed reddening of the branches a week and a half ago - the trees are responding to the longer days, despite the cold.

  4. Francis Keem II
    Apr 05, 2017

    I have a question. Usually on my first boil of the Season I produce light maple syrup or otherwise known as gold and delicate. However that is usually the only time it happens. After that my syrup always moves into the medium grade. I can’t believe that my stuff gets that dirty just from one run. Any suggestions?

  5. Dave
    Apr 06, 2017

    Cleanliness and speed are your only means of affecting grade. Do you use buckets or tubing? If buckets, make sure you collect them quickly, store the sap in a cool place, and boil it in a timely manner, i.e. that day. If you use tubing, it needs good pitch, the tubing should be replaced regularly, avoid black mainline, use vacuum if you have the scale to make it cost effective, if not experiment with 3/16ths diameter tubing and create natural vacuum. Look at the sap as if it were as perishable as milk. Or, just resign yourself to the idea you make dark syrup and tell your customers it tastes better and they don’t want the light stuff anyway.

  6. Taylor Bishop
    Oct 30, 2017

    Thanks for the interesting read about syrup. I actually didn’t know that the amino acids in maple sap increases as the sugaring season goes on. I’m interested to learn more if this is the case for different areas, or how the climate could affect how many amino acids there are.

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