Breakfast, Read, Winter, Spring, Fall

Maple Syrup Science

When the weather changes, and the air becomes crisp with wintery anticipation our minds turn to the burnished flavors of fall. Apple, cinnamon, pumpkin, and that king of all syrups: maple. At some point in our lives each of us has pulled a bottle of the liquid gold off the grocery store shelf and marveled at the price tag. Indeed, maple syrup is a costly item, but one that is more than worth the investment.

But why is maple syrup so expensive? Consider this: maple syrup is made from the sap of maple trees (natch), but it takes 10 gallons of sap to produce just one quart of syrup! The ratio (40:1) is astounding and explains the cost, but hidden in that ratio is also the marvelous science of this sweet treat.

Let’s first turn our eyes toward the biology of tree growth. During the summer when the sun and heat are at their apex, leaves convert light into sugar through photosynthesis and implore the tree to grow. Excess sugar not used during the summer season is stored in the trunk to protect the tree through the colder months of fall and winter. That trunk-bound sugar is what we tap in the spring to release maple sap.

And how does the sap flow from wooded trunk into patient bucket? Maple farmers drill holes into the trees, then insert spiles. A spile is a metal spigot or funnel inserted directly into the bark that directs sap flow. You might remember that a spile is what saved Katniss Everdeen in the beginning of the second Hunger Games novel. Or you might not remember that. Which is good, because it means you were either wise enough to avoid the books altogether, or that you are not so much a nerd as I and don’t fixate on tiny, scientific details. 

But sap won’t flow out of a tree unless the environmental conditions are perfect. We tap maple trees in the spring because the trees are subject to below freezing temperatures at night and warmer climates during the day. That back and forth of freezing and thawing is exactly what we need for sap to flow. The trees suck up water from the soil during the day, then at night it all freezes with the sugar in solution inside the trunk. The following morning, as the sun rises and temperatures crest 40 and 50 degrees, the water inside the trunk melts, then warms up. The pressure differential from cold nights to warm days helps the sap drip into collecting buckets.

Remember: the sap that we collect is 40 times waterier than the syrup that is eventually sold. So once we have buckets and buckets of sap, it’s time for chemistry to take over. Maple sap is basically a weak concentration of sucrose in water. The sap is boiled to evaporate excess water and further concentrate the sucrose. As more and more water is removed, the ratio of sugar present in solution increases. The colors and flavors that we associate with maple syrup are due, in part, to the heat applied during this concentration phase.

Sucrose itself is not a terribly reactive sugar, but its constituent parts (glucose and fructose) are quite excitable. Microbes present in the sap break sucrose down, and then as heat works on the glucose and fructose we see the effects of sugar degradation: color change, caramelization, increased viscosity.

Maple syrup has been collected for centuries, and it is a uniquely North American crop. The indigenous people of this continent figured out how to collect and concentrate the sap from maple trees, knowledge which they passed along to European settlers. Today, nearly 80% of the maple syrup sold around the world is collected in Quebec (which has the perfect climate for the trees). 

Maple syrup used to be separated into grades, which correspond to color and flavor. But as of 2015, a new rating system has been put in place. Now as long as there is no sedimentary cloudiness impeding the translucency of the syrup, it is all marked Grade A. Within that A grading there are four distinctions: Golden, Amber, Dark, and Very Dark. The grading is now based purely on translucency (that is, how much light can pass through the finished syrup). The darker the syrup, the more pronounced the maple flavor will be. Lighter syrups usually come from the early part of the season. 

And now back to pricing: Because the syrup is so prized, and because the yield from sap is so low, the maple growers in Quebec banded together to create a maple syrup reserve. Yes, much like the oil producing countries of OPEC, the Federation of Quebec Maple Syrup Producers (FPAQ) maintain the International Strategic Reserve of syrup (ISR). This glut of syrup is stored as a buffer against bad seasons and to help control global pricing and supply. There are obvious benefits and consequences to such an alliance, but I choose to look on the bright side. Isn’t it wonderful to know that there are roughly 13,000 tons of maple syrup safely protected in rural Canadian facilities? Our tastebuds are being watched over: should the weather fail, or the syrup run dry one season, the great gastro-treasure of maple syrup will still be on our shelves.