Making maple syrup is a simple process. There is one ingredient: maple sap. Maple sap is not the sap most people imagine when thinking about sap-typically the pine sap that is more like tar comes to mind. Maple sap is similar to sugar water, somewhere between 1.5% and 3% sugar along with a host of beneficial micro-nutrients and minerals such as manganese. The process of creating maple syrup is governed by the goal of collecting the low sugar percentage sap and converting it to the high sugar percentage syrup. Between 67% and 69% sugar is considered maple syrup. At this percentage the syrup is shelf-stable in that it will neither spoil (if the sugar percentage were too low) nor crystalize (if the sugar percentage were too high). To bring a batch of maple sap from an initial 2% to a final 68% sugar percentage requires a factor of about 50-1 for sap-syrup ratio. To make 2 gallons of maple syrup you would need 100 gallons of maple sap. The tool for measuring sugar percentage is called a hydrometer and the metric used for sugar percentage is called ‘brix.’
To tap a maple tree in a sustainable way the main stem of the tree needs to be 10 inches in diameter at a height of four feet off the ground. Typically a maple tree is 20 to 25 years old by the time it gets this big. A portable drill with a 5/16” bit is used to make a 1.5” deep hole in the tree at the beginning of the sugaring season. After drilling the tap hole you place the tap, which has a barb on it with the correct diameter to create a seal, within the hole and tap it with a hammer a few times to seal it. This allows sap to flow directly from the xylem of the tree and out the tap hole via a spout into a bucket or sap line. Tapping in this manner does not hurt the tree in any significant way and a healthy maple tree can be tapped for over 100 years! Depending on the size of the tree it will have one, two, or three tap holes each season. The timing of when to tap the trees varies year-to-year based on how quickly warm weather happens at the end of winter. You need consistent above freezing temps during the day and freezing temps at night. The sugaring season is only five to eight weeks long so you want to get the timing right...you don’t want to tap too early or too late. As the season progresses, natural bacteria in the tap holes reduce the amount of sap that flows from the trees. Tapping early, say in the middle of February in northern NH, increases the chances that you will be getting smaller yields at the end of the season due to the natural bacteria. Conversely if you tap too late you may miss out on early season sap runs which sometimes far outweigh the benefit of getting full yields at the end of the season. It is a delicate balance and sugar makers create much debate about when to tap. The answer is, as with many things in farming and life, it depends!
Depending on the size, scale, and efficiency of the operation, collection of maple sap can be done in many different ways. Our sap flows downhill via sap lines which are designed much like a vascular system with small lines leading from the tap holes in the trees to larger ‘main lines’ which carry the sap directly downhill to large containers. If the container is large we can pump the sap into a collection tank in the back of a truck. Some lines are smaller and only have 5 to 15 taps on them and lead to five gallon containers that we can replace and carry to the truck. We still use about 75 traditional sap buckets. Each bucket might have about a gallon of sap at the end of a good sap run so we bring along a couple of five gallon buckets and aggregate the sap buckets to reduce trips back and forth to the truck. It’s a lot of work carrying sap but also good exercise!
The evaporator we use to boil is a stainless steel unit about 10 feet long and 2.5 feet wide. The purpose of the evaporator is to boil off water in an efficient manner. To turn 100 gallons of 2% sap into two gallons of maple syrup would take a couple of days on a kitchen stovetop and takes less than an hour on a reasonably efficient evaporator. The key to this is having a large ‘surface area contact’/liquid volume ratio. Basically this means getting as little amount of liquid (maple sap) at a given time touching as much extremely hot stainless steel as possible to maximize the evaporation rate. As the steam is boiled off and vented through wide and tall steam stacks that create excellent draft, the liquid level- usually just a couple of inches high - is maintained by a float valve that connects the ‘head tank’ (unboiled maple sap storage unit) to the evaporator. The float requests sap from the head tank at a steady rate as the steam boils off. The sugar molecules, thankfully, do not get released in any significant amount with the steam and so they steadily accumulate and get pushed forward in the evaporator as fresh sap flows in past the float valve. This process is known as the ‘gradient.’ The gradient makes it so the liquid farthest along in the evaporator will exist at a higher sugar percentage and thus reach the sugar percentage of maple syrup first, rather than all of the liquid in the unit increasing in sugar percentage simultaneously as one might otherwise expect.
When the sugar percentage in the final pan of the evaporator reaches 68%, which can be roughly measured by the boiling temperature of maple syrup being 7 degrees fahrenheit hotter than boiling water, 219 vs. 212 degrees, you draw off the unfinished syrup into a finishing tank. When the finishing tank is full, it’s time to fine-tune the maple syrup to the exact sugar percentage you’re aiming for. You either slightly concentrate or slightly dilute the batch of syrup by boiling on a propane burner or adding in low concentration syrup from the evaporator to reach the desired sugar percentage.
Unfiltered syrup will have sediment-type material in it such as niter (essentially sugar solids). Providing crystal clear syrup is an important thing for maple syrup producers. We are producing a luxury product and a crystal clear appearance is part of how that is communicated. The way to guarantee crystal clear syrup is to use a filter press. Utilizing the same basic technology as ancient civilizations used to filter wine, a maple syrup filter press forces the maple syrup evenly across waffle plates, each of which has a filter paper pressed against it that is pre-charged with diatomaceous earth (DE). The DE builds a ‘cake’ layer on the filter paper and forms a complex matrix that traps suspended maple syrup solids while allowing maple syrup to pass through. No DE makes it through the filter press, either, so what you get is 100% pure maple syrup.
The filtered maple syrup flows to the bottling unit. The bottling unit is a stainless steel tank that has a built in thermometer and a low-level propane burner under it to maintain a temperature of between 180 and 200 degrees fahrenheit. Syrup gets bottled between these temperatures to guarantee no bacteria survive in the bottle and also to guarantee that niter does not form which can happen at temperatures over 200 degrees. After the bottles are full they are capped and turned on their sides to guarantee a successful seal.