A Simple Model of a Vacuum-Tubing System for Collecting Maple Sap

Abstract

To produce maple syrup, one must first collect the sap from the tree. Traditionally, maple trees were tapped with spiles that had a bucket attached to capture the sap as it flowed out. However, research and advances in technology have given rise to a more efficient method of sap extraction: vacuum-tubing systems. This technique of sap extraction leverages the physics that allows for sap flow in the first place, creating larger yields from the tree throughout the season. Sap exudation is caused by the freeze thaw cycle that takes place in the early spring season. The xylem from a maple tree contains sap (a byproduct of photosynthesis) and gas bubbles, and acts as a pipeline for transporting water throughout the tree. When temperatures drop below freezing, there is a negative pressure in the tree relative to the atmosphere, which draws water in from the roots. When a thaw occurs, there is a positive pressure in the tree and the gas expands in the xylem. This expansion coupled with an osmotic sugar concentration gradient causes sap to flow out from the fibers. When one taps into the xylem, there is a larger wound for the sap to flow out of, and more sap can escape from the tree. By attaching a tubing system to the tap, and removing air, one can increase this pressure gradient between the tree and the tap hole, which both increases the range of temperatures sap will flow, and the flow rate of sap during those runs.

The following model was created to estimate a conservative yet realistic vacuum tubing model for sugarmakers of varying sizes, for the purpose of assessing the energy and emissions impacts of the entire production process. The methods are adapted from The New York State Maple Tubing and Vacuum Notebook (NYS Notebook) out of the Cornell University Extension Cooperative. Their methods were altered to create a tubing model for different producer archetypes (characterizations of the industry based on production scale), meaning they are modeled without sugarbush data. Below is a breakdown of the assumptions made when modeling these archetypes, and the physical principles that underlie them. While producers may be able to use this as a tool to optimize a tubing network, this model is primarily used to estimate the amount and diameter of tubing used at different production scales.