by Deborah Jeanne Sergeant
Maple syrup flavor varies among producers, not just from year to year. Aaron Wightman, maple specialist with the Cornell Maple Program, has participated in judging the syrup competition at the New York State Fair in the past.
“We get 75 or 100 submissions of what people think might win the ribbon,” he said. “About 75% of those samples have an ‘off’ flavor.”
Considering those samples represent the best of their best, that is a sobering thought for producers. “Even though we’re individual maple producers, we put our products out on the shelf with the label of pure maple syrup,” Wightman said. A bad experience with one maple brand effects the entire industry.
Wightman said there are a lot of ways to improve the syrup. He presented “Tips for Top Quality, High Flavor Syrup” as a recent webinar hosted by Cornell and the USDA National Institute of Food and Agriculture.
Many factors contribute to syrup flavor development, from sap chemistry to chemical reactions. “Understanding how flavor develops is critical to enacting quality control measures in maple syrup production,” he said. “The raw ingredient for syrup is sap, and not all sap is the same. Factors such as soil type, tree genetics and tree health all affect the composition of sap. Differences in composition lead to differences in flavor.”
Wightman said maple syrup has two flavor control points: failure points for damaging flavor and points where flavor can be enhanced. He listed sugarbush health, sap collection and handling, evaporator and syrup processing and packaging all as failure points.
“Soil type and soil conditions have a large influence on mineral content, as well as the types of organic and inorganic acids, present in sap,” Wightman said. “Although these compounds typically represent less than 1% of the sap, they do have a role in flavor formation.”
The genetic makeup of individual trees can also matter. “Trees are unique individuals, just like humans,” Wightman said. “Their genetic makeup, along with the growing environment, determine sugar content and sap chemistry, among other things.”
He added that stressors including insect damage, disease and drought “all initiate responses from the tree that alter sap chemistry.”
Sap changes after it is tapped. Wightman called it “a living biological medium populated by microbes such as bacteria and yeast. As these microbes live and multiply in the sap, they slowly change its chemical composition.” That is why careful handling of sap is so important.
Wightman explained that sucrose is the only sugar in sap when it exits the tree. Microbes can convert it to glucose and fructose through fermentation. These are commonly called invert sugars in the sugarmaking industry and are responsible for the product’s darkening and flavor development during evaporation.
“Invert sugars behave differently than sucrose when subjected to the heat of cooking,” Wightman said.
Caramel reaction with sucrose starts at 365º F. With glucose, it’s 295º; with fructose, it’s 219º.
“Caramelization describes a class of chemical reactions that take place when sugar is subjected to heat,” Wightman explained. “Caramel is one of the most prominent flavors in maple syrup.” Higher invert levels in sap will result in darker syrup with more caramel flavor.
Microbial activity can cause both positive and negative effects on syrup flavor. “Of particular interest is the fact that trees have a complex physiological response to injuries and disease,” Wightman said. “Areas of infected or damaged wood are sealed off and flooded with a variety of compounds that inhibit damage proliferation. Some of those compounds, including a class of chemicals called phenols, can impact flavor.”
Sap handling also makes a difference in syrup flavor. Wightman said that dirty tubing or buckets, sagging lines and using non-food grade containers and fittings can contribute to lower quality, especially since odd flavors become concentrated in syrup.
“Sap sometimes spends a significant amount of time within the collection system,” he said. “Therefore, the conditions within the system can impact flavor quite a lot. Dirty tubing or buckets can quickly impart yeasty and moldy flavors. Sagging mainlines slow sap flow to the sugarhouse and can lead to more spoilage in the lines. Any component that is not food grade may also impart bad flavors to the sap.”
Using liquid bleach in a concentration of one tablespoon per gallon of water for 20 minutes’ contact time, followed by a thorough rinse with clean water, should suffice in cleaning the lines.
Processing also makes a big difference in the end flavor of the product. “Scorch is one of the most common defects,” Wightman said. “This happens when the temperature gets too high in some part of the evaporator and the sugars in the sap burn. Just a little scorching has a big flavor impact and makes the whole batch of syrup smell like smoke.
Many producers use defoamer to prevent their sap from boiling over; however, Wightman warned it should be used sparingly, since it can not only leave an oily flavor, but also a “waxy” feeling in the mouth.
Producers using a wood-fired evaporator should take care that smoke does not contaminate the syrup.
“Maple syrup is a delicate flavor,” Wightman said. “When exposed to unclean air it quickly absorbs contaminants that show up in the flavor. Smoke is a common exposure agent, especially with homemade hobby rigs. Make sure smoke is properly vented away from your arch to avoid this problem.” (Commercial evaporators have measures built in to avoid this problem.)
If the flavor is too light, the process needs more oxygen. If it is late season sap (which typically creates darker syrup) or off-flavored, adding oxygen may help too. The three methods include diluting the finished syrup and re-boiling to the right density; boiling above standard density and adjusting back to 66 brix with water; and pressure cooking to higher temperature.
“You can make a robust flavored syrup with about anything,” Wightman said. “Each of these methods requires a little bit of care.”
The way syrup is handled after boiling can also impact flavor. “Syrup must be filtered in order to be compliant with grading standards,” Wightman said. “All of the rules that apply to sap filters also apply to syrup filters. Using a filter press rather than cloth filters will avoid some of these issues and filter sap more effectively.”
Bottling containers must be food grade and meant for high temperature use, since syrup is hot packed in containers sterilized at 180º.
A webinar participant asked about his very dark syrup made in March 2019. It had a caramel flavor, so he tried to use an aerator to place bubbles in the sap feedback. Since it did not mask the caramel flavor, he wondered if more air would have made a difference.
“You can’t bring it back with aeration,” Wightman replied. “You could try refrigerating your sap. The development of strong flavor later in the season is really hard to revert back.”
Another question was about storing syrup in barrels and not in refrigeration. The producer does not package all his syrup in small containers at once. “Can you replace the air with an inert gas to keep the bacteria down so you don’t have to use the whole barrel?” he asked.
Wightman, who bottles his syrup all at once, speculated that nitrogen may help. Another participant said that may make sense, as it works with other foods. “There are some possibilities,” Wightman added. “I know some producers put a shot of nitrogen in their bottles to prevent the layering effect when you see a few layers of colors.
“A lot of people buying ultrafiltration units are storing sap a long time or are bottling sap as a beverage. The ultrafiltration units … will do five gallons per minute and you have to change the filters a lot. You would have to do it after reverse osmosis, not the sap.”
Cornell researchers are working on alternative sugar production methods. For example, very dark syrup usually does not make maple sugar, as it requires low invert syrup that can crystalize.
The appearance of syrup matters. “It’s counterintuitive that a gourmet product is rated on the color rather than the flavor,” Wightman said. Nonetheless, consumers expect a certain color for their maple syrup.