Off-Tasting Syrup: Understanding the Culprits (Part 3)

Now that we have talked about tree phenology and maple buds and growing degree days, let’s the talk more about the main prize of every sugarmaker’s dream – QUALITY syrup!  As we get ready to embark on a new maple season, let’s go over some of the things that will help you to improve the quality of your syrup in 2022. We all know that paying attention to detail in the woods will pay off with big rewards; however, the place where paying attention to detail is most important is when the sap or concentrate is on the evaporator. The finishing process can make or break your operation. Maple production is becoming a very competitive business, and the producers making the highest quality syrup will rise to the top.

Here is an oversimplification of what happens during the syrup-making process.  Once bacteria are introduced into the sap, a conversion of sugars takes place. A portion of the maple sap, which is almost 100 percent sucrose, is converted into glucose and fructose. This portion of the sugar content makes up the invert sugars present in syrup. When the sap is heated (The Maillard Reaction – something you can read more about here) the color of the syrup and the flavor of the syrup is formed, largely based on the amount of glucose and fructose sugars and other factors happening at the same time.  Thus, the level of microbial interaction plays a vital role in determining the color, grade, and corresponding flavor profile of the syrup produced. So, as you can see not all microbes are bad, in fact they are essential to everything we love about maple syrup!

Sap flowing from the maple tree is sterile, so where do the microbes come from?

Microbial activity begins as soon as sap is exposed to the outside environment. Early in the season microbial development is slow due to the normally cold temperatures, but once warm weather arrives (above 50 degrees F), more and other strains of microbes begin to multiply in the sap. As the microbes interact with the sap, the syrup produced darkens and develops an increasingly bold and pronounced maple flavor. Microbe colonies continue to expand eventually resulting in very dark and viscous syrup with an unpalatable strong flavor. Because this degradation of the sap is more likely to occur at the end of the season, low quality syrup is often associated with tree budding which happens at approximately the same time.

If you did a taste comparison, you would notice is a definite difference between buddy syrup and sour sap syrup. Buddy syrup has a chocolate flavor akin to what a Tootsie Roll tastes like while sour sap syrup has a bitter sometimes fermented taste that stays in your mouth. If you boil buddy sap, it will produce a pungent unforgettable smell. Sour Sap thickens to the point where it cannot be evaporated and will be difficult to draw off the evaporator. In extreme cases, you can pour a stream out and it will suspend in midair. This is referred to as “ropey syrup”. Sour sap is a result of intense microbial activity that builds anytime during the season when environmental conditions are right for bacterial growth. Buddy syrup comes from sap collected when the buds emerge naturally from the tree. This is a normal physiological growth stage that occurs every year.

Both processes require and progress with seasonal warming. In a normal season, the two tend to occur simultaneously and accelerate at the end of the season. Though the two are correlated, it is important for producers to understand the differences if you want to avoid the problems associated with each.