Before new technologies better defined sap volumes, the best measure to calculate was known as the Jones Rule of 86. With assistance from just a sap hydrometer and cup, all that was needed was to determine the number of gallons of sap required to make 1 gallon of maple syrup was to divide the number 86 by the percent of sugar content.

The equation is the origin of the reference ratio of 40 gallons of sap producing 1 gallon of syrup. The originator, C.H. Jones, an educator at the University of Vermont, came up with the equation in the early 20th century. Decades later, it was published as a rhythmic poem titled, “Maple Rule of 86,” that noted specific instructions like:

Seems easy, right? In a day before the internet and smartphones, probably so. But today, new tools utilizing reverse osmosis are becoming more common, plus historically, finished maple syrup had legally minimum densities of 65.5 degrees Brix. Now, it’s up to 66.9 degrees Brix in some states. Yes, a slight increase, but enough to throw a producer’s calculations off track.

Thus, the old rule of thumb has been slightly adjusted. Timothy Perkins and Mark Isselhardt of the University of Vermont Proctor Maple Research Center gave the rule a tune up by using the 87.1 adjustment for 1 gallon of syrup at the 66.0 degrees Brix and 88.2 for syrup at 66.9 degrees Brix.

Original Jones Rule of 86:

Most sap has about 2 percent sugar content.

86/2 percent = 43 gallons of sap needed for 1 gallon of syrup.

34.4 gallons for 2.5 percent; 28.7 gallons for 3 percent.

Source: University of New Hampshire Cooperative Extension

For high-value sap, accuracy is key for sugarmakers and can be the difference in providing quality product as explained by Butternut Mountain Farm during its 2015 run:

“At the start of the season this year at our sugarhouse, the first couple of runs averaged a sugar content of 1 percent — meaning that it’d take approximately 86 gallons of sap to make 1 gallon of syrup. Last week the sugar content had increased to between 2 and 2.4 Brix. On Sunday it had improved further to 2.8 to 3 Brix, which is high. At 3 Brix it’ll take about 28.7 gallons of sap to make a gallon of syrup. With the improving sugar content, shorter, sweeter runs will take less sap volume to make a gallon of maple syrup.”

Perkins and Isselhardt noted in their research that the relationship changes for higher sap sugar concentration and that buyers and sellers can adjust accordingly.