The Surprising Science Behind Maple Syrup Production
And a love letter to Samin Nosrat
I’m usually a little late to the game in terms of TV shows or movies and not quite sure why. I see something interesting, but of course, can’t start something new until I finish what I’m already watching. Then I get distracted or go for something I’d wanted to watch an even longer time ago, so I hardly ever watch a show as it’s actually running.
Anyway, I’d recently gotten around to watching Salt Fat Acid Heat with Samin Nosrat on Netflix (and totally plan on buying the book). Samin’s passion for food and people, her enthusiasm and energy were absolutely infectious and inspiring. I think she’s inspired a lot of people, hence the popularity of her cookbook and this subsequent mini-series. I’m only…6 years behind the game, but hoping Samin won’t be mad about it.
Obviously, this is no place for spoilers, but I will say the deep-dives into how certain food things (like soy sauce?!) are fascinating. And among all of these little epiphanies, I remembered a childhood curiosity that I’d somehow never let go of: how maple syrup is made. Also realizing that I now live in Boston and it’s VERY possible to experience this, I booked a tour at the historic Appleton Farms and dragged my sweet-toothed fiancé along for the ride.
While it may have technically been a sunny first day of spring, the wind was absolutely brutal. It ripped through wide open hills with nowhere for us to hide. We definitely pulled the short end of the maple branch – frozen, wind-whipped and sunburnt at the same time. I’d love to add in “...but we were troopers” but the truth is, the tour was also filled with children who complained a lot less than I did.
This time of year is critical for maple syrup production, usually happening between late winter and early spring for Massachusetts, but fully depending on outdoor temperatures. It could even start as early as January. Temperatures need to be freezing at night, but above freezing during the day. Sap is collected by drilling a shallow hole hip-height into the trunk of a mature sugar maple tree (about 40 years old). This is where it gets wild.
Most hard wood trees (TIL there are hard and soft wood trees) leak sap when they freeze due to the expansion of water molecules in ray cells that move and store the life-giving starches. However, the ray cells in maple trees are filled with gas, not water like the other hard wood trees. When this gas freezes, it condenses and causes a negative pressure within the tree, much like drinking from a straw. Combined with colder, more dense air and higher atmospheric pressure outside, the sap is squeezed up through the tree. When the temperatures warm up above freezing, the extra sap flows back down the tree thanks to gravity and the reexpansion of gas. This excess sap is collected through the tap at this point. The Vermont Evaporator Company has an excellent article and further references if you’re interested.
We walked through the sprawling grounds with our guide pointing out the dairy barn, carriage house, site of the Appleton family’s mansion and one of four columns rescued from the original Harvard building during its reconstruction. We stopped in the sunshine and examined a covered blue bucket hanging from a maple tree and discussed the fact that Native Americans had been producing maple syrup long before European settlers arrived (although the actual discovery story remains more of a legend). Native Americans would make a V-shaped slash in a tree to gather the sap and either leave it out to freeze, or boil it with hot rocks. This removed the water content of the sap, leaving behind the sweet maple sugar to be used for cooking and trading. We were all a bit surprised to find that this sap was a clear, watery liquid with a couple dead bugs floating in it. Not as sexy as we thought it would be. That part comes next.
We were relieved to trek back to the tiny sugar shack filled with warm sweet-smelling steam. The sauna of my dreams. It was manned by the nicest guy ever, who explained the production process. He stood behind a small wood-fired evaporator and tried to prevent the kids from touching it.
The gathered sap is poured into one end of a deep pan divided in three sections, but only filled to an inch or two. It is constantly fed sap to keep it at the same level. Here, the sap is boiled to remove the water content, concentrating the sugar content from the original 2-3% until it is between 66 and 68%. It takes about 40 gallons of sap to make one gallon of maple syrup. While there are different types of pans and styles, this particular evaporator had a continuous boil pan. This allows the syrup to travel through different sections of the pan as the sugars caramelize and density increases. In the third and final chamber, the syrup can be released from a spigot after reaching the desired sugar level, where it can be filtered and bottled.
Our host told us excitedly about the different color and flavor grades of syrup, holding a box filled with 4 different samples to the light. Golden syrup is his favorite and he likened it to extra virgin olive oil – the first few rounds of syrup produced earlier in the season. This style is due to a variety of factors, but largely attributed to the higher sugar content in the sap at this point in the season.
Once the sap is collected, the sucrose molecules can be broken down into fructose and glucose by ambient yeast and bacteria in the air. These are the sugars that are browned during the evaporation process. According to the University of New Hampshire, “the warmer the air and sap temperature, the more active the microbes, the more sucrose that gets converted.” This leads to a darker color and richer flavor, as opposed to the golden color and lighter flavor. We also know that if there is a higher amount of water content in the sap, it will need to boil for a longer period of time to reach the appropriate sugar concentration, also contributing to a darker color. While it’s all the same grade, quality and sugar content, the flavor profile is totally up to personal preference.
We stuck around after the tour to explore the recreation of the mansion’s library and historic photo albums. Then of course, we drove over to their small storefront to grab a souvenir of amber syrup. We can confidently say this is the best syrup we’ve ever had and look forward to trying more locally-produced brands.