When we pour maple syrup on our morning pancakes, we want to believe that it is — as the label often says — “100 percent pure.” But how do we know for sure? Pure maple syrup is expensive to produce, and unscrupulous syrup producers can sometimes adulterate their product with small amounts of cane or corn sugar, hoping consumers won’t notice. The underlying chemistry, however, doesn’t lie. With the help of techniques stemming from geology, Colgate professor William Peck has been helping to put the kibosh on fake syrup.

Peck’s day job is rocks. As professor and chair of the geology department at Colgate, he specializes in measuring isotopes of common elements like carbon, hydrogen, and oxygen in order to determine how rocks in mountain belts were formed. Unlike unstable radioactive isotopes, which degrade over time, stable isotopes are normal atoms, with some having an extra neutron or two that makes them slightly heavier. “Our solar system was born with a certain amount of stable isotopes and it will die with that number,” Peck says. “Chemical reactions aren’t going to change that.”

A collection of glass jars of maple syrupIsotopes of chemicals do behave slightly differently, however. For example, when water evaporates, the lighter isotopes evaporate first, so Peck can look at rocks millions of years old and determine whether the fluids that shaped them came from rainwater or leftover ocean water. Peck conducts this research with a mass spectrometer, a hefty piece of lab equipment that ionizes small samples and sorts their component elements by mass. About 15 years ago, he realized that in addition to looking at rocks, he could use the instrument for measuring something a bit less ancient — the component elements of maple syrup. “I wanted a cool project that students could relate to, and it would be easy to collect the samples,” he says.

When maple trees conduct photosynthesis, they preferentially take lighter carbon from the atmosphere to make carbon dioxide. The way that maple trees (and indeed, most plants) photosynthesize carbon, however, is slightly different from the way grasses such as corn and sugar cane photosynthesize, causing the latter to contain more of the C-13 isotope of carbon over the more common C-12. “You could use that fact to tell what broad group of photosynthetic style a sample belongs to, just like a fingerprint,” Peck says.

Such analysis could tell how much of a sample was maple syrup and how much was adulterated with corn or cane syrup from the percentage of C-13 isotope found there. In order to examine this property with students, Peck obtained dozens of syrup samples from New York and Vermont, including some historic samples dating back all the way to 1970. Although he and the students didn’t find any evidence of adulteration, they did find something surprising: the percentage of C-13 in the samples slowly decreased over time.

“When you have a lab with the ability to measure certain things, it’s one of the pleasures of research to see what goes on in these other niches of science.”

Peck blames the same increase in CO2 in the atmosphere that has led to climate change. As pollution has injected more CO2 into the atmosphere, plants and grasses have been able to obtain more of the preferential C-12 carbon, decreasing their uptake of C-13. While isotope studies have been used by regulators to test food authenticity since the 1980s, Peck’s findings imply that, because of those atmospheric changes, the bar for testing has shifted over the past 30 years, potentially skewing results. “The atmosphere moves all of the trees away from the threshold set to test adulteration. You could sneak in 5 to 10 percent corn syrup, and no one would know,” says Peck, who published his results along with former student Stephanie Tubman ’08 in the Journal of Agriculture and Food Chemistry in 2010.

The sky through birch treesIn more recent research, Peck has expanded the techniques to look at other kinds of syrup. A paper written with Colgate students Erin Cumming ’16 and Ellis Van Slyke ’17 and published in August 2018 in the Journal of Food Composition and Analysis explores whether the same analysis could be applied to birch syrup — a more expensive and increasingly popular savory syrup sold in the United States and Europe. “You might not put it on pancakes, but you might use it to marinate salmon,” Peck says. Due to its strong taste, producers often mix it with sweeter syrups to make it more palatable. Their research shows that, indeed, isotope analysis could be used to determine the amounts of corn and cane syrup in a birch syrup blend. Since maple and birch syrup use the same photosynthetic pathways, however, a different type of chemical analysis would be needed to determine any amount of added maple syrup.

In the meantime, Peck continues his research on rocks, examining the geological composition of high Adirondack peaks, even as he enjoys his sideline as a food chemist. “I have a friend who teases me about this at geology conferences, saying ‘How is your condiment research going?’” he says. “But when you have a lab with the ability to measure certain things, it’s one of the pleasures of research to see what goes on in these other niches of science.”