Why are there different grades of syrup?
One of the most common questions we get asked at farmers markets is "Why are there different grades of maple syrup?". The answer to this has fascinated chemists for quite some time, and something that we find pretty interesting. Our application of the science of syrup production, and careful choices made for the benefit of the consumer, allows Sterling Valley Maple to offer you a product with superior flavor and color to meet each taste preference.
The colors (and most of the delicious maple taste) in syrup are generated during the boiling process as the last of the water is removed from the syrup. Two chemical reactions are in play during this process. The first is caramelization. Caramelization is a process in which sugar is heated and turns brown. The chemical reactions are complex, but they result in flavors being generated as the sugar is heated and subjected to other chemical reactions.
There are three kinds of sugar in maple sap: sucrose, glucose, and fructose. Glucose and fructose are sometimes referred to as simple (or monosaccharide) sugars, and contain six carbon atoms each. When a fructose molecule and glucose molecule are bonded together, they form a sucrose molecule (which is the sugar present in table sugar). Sucrose is much less reactive than glucose and fructose. In fact, fructose begins to caramelize at temperatures 90 degrees cooler than sucrose. So, the more simple sugars that are present in sap, the more caramelization will take place during the cooking process.
The second process that produces flavors in syrup is the Maillard reaction. This process was named for a French chemist who described it about 100 years ago. It is a process where amino acids are heated to produce a brown color and literally hundreds of different flavor compounds. The more amino acids that are present in the sap, the more the Maillard reaction will occur and the more flavor compounds are produced.
As you can see, changing the ratio of complex to simple sugars, and increasing the presence of amino acids are the two variables that affect the final flavor of the syrup. Amino acids tend to increase as the maple season progresses- simply put, the trees come out of dormancy and start to release more of these proteins later in the season. Syrup made later in the season will naturally have more of the complex flavors produced by the Maillard reaction. The caramelization reaction is more nuanced: when the sap leaves the tree, almost all of the sugar in it (regardless of when in the season it is produced) will be sucrose. However, that sucrose almost immediately begins being broken down by enzymes. The warmer the weather, the faster these enzymes work. The more time between the production of sap and the cooking of the syrup, the longer the enzymes have to work. So, even early in the season you can produce a darker syrup with stronger flavors if the sap is allowed to age prior to cooking.
One final variable in the process is cooking time and temperature. Sap that has been processed by a reverse osmosis machine to have a high sugar content will spend less time in the evaporator than sap that begins the boiling process at a lower sugar content. Although there haven't been many studies on the effect this has on flavor, we believe it is important for syrup to boil long enough to develop the richest possible flavors. Because of this, we limit our use of reverse osmosis by only concentrating the sap until the sugar concentration reaches 8%. We feel this provides a good balance of efficiency while still allowing the syrup to cook for significant time in the evaporator. We also use a traditional wood-fired evaporator. While a significant benefit of oil-fired evaporators is their steady, even heat, we believe that the "hot spots" created naturally in a wood-fired evaporator are actually a good thing, allowing the cooking sap to be exposed to higher temperatures and accelerating both of the chemical reactions that produce the characteristic maple flavors.