Maple syrup is graded by light transmission, or color. Syrup changes color as temperature and time play with the sap.
The coloring of syrup is affected by several factors and each factor can influence another—it gets complex. The pH of the boiling sap, sugar concentration, types of sugars in the sap, length of boiling time to produce syrup, the temperature outside, and even microbial activity all play a role in syrup color.
The most common form of sugar in sap is sucrose –a complex, stable form of sugar. Once the sap is outside the tree the sucrose molecules are exposed to naturally occurring bacteria and yeast that break down sucrose sugars into simpler fructose and glucose sugars. The warmer the air and sap temperature, the more active the microbes, the more sucrose that gets converted. These converted sugars can go through a Maillard reaction or “browning” process while sucrose doesn’t. The bacteria and yeasts are killed during the boiling process.
Maillard reactions are the same reactions that browns the crust of baked bread or gives French fries that golden color. They also provide the coloring for maple syrup. The more glucose and fructose sugars in the boiling sap and the longer the sap boils, the darker the syrup will be. Sap with lower pH also breaks down sucrose, resulting in more glucose and fructose. Furthermore, the concentration of sugar in sap influences boiling time. The higher the sugar content, the shorter the boiling time. When the sap is exposed for less time in the evaporator, there is less time for browning resulting in a lighter grade of syrup.
In short, Golden syrup, in part, is a product of sap that has had little microbial activity either because of lower temperatures and/or sanitary sap handling. It’s quite common for sugarmakers to clean their equipment often throughout the season to keep the syrup from getting darker. It’s also common for them to be happy if there is a good cold snap in late March, as the frigid nights can lighten up the syrup. Likewise, as the season goes on, temperatures build, sugar content in the sap declines, microbial activity increase, and the syrup color darkens.
Preference for a flavor comes down to personal taste. Most folks enjoy the Dark and Very Dark grades of syrup due to the robust and strong maple flavors. Those grades tend to be produced later in the season when it takes longer to make syrup due to lower sugar contents. This longer boiling allows for more flavor to develop and Maillard reactions to occur, during which color and flavor are developed. The flavors found in Golden and Amber syrups have some developed maple flavors but are mild in comparison because the boil time is less, and sucrose levels are higher. The mild and delicate maple flavors allow for other organic substances found naturally in maple sap to be part of the flavor profile. Besides boiling time and sap composition, soils, tree-health, sap handling and processing, and weather can affect flavor development and give unique flavors to every sugarhouse.