Timothy D. Perkins, Ph.D
Director of Research
Proctor Maple Research Center, University of Vermont  

Maple equipment manufacturers recently introduced a new variety of spouts which are smaller than the standard spout used in sugar making.  Whereas the standard spout is 7/16" (left) in diameter, the new spouts are 19/64" (right) and 5/16" (not shown).  We compared sap yield, taphole closure, and tree wounding caused by the standard and small spouts under both gravity and vacuum conditions.  This report presents the preliminary results of our work over two sapflow seasons.

During the 1998 season, we collected sap from small trees (5-11" diameter) using the 7/16" and 19/64" spouts under gravity using buckets (photo right).  We also examined the effect of taphole depth on sap yield by drilling tapholes at 3/4", 1 1/2" and 2 1/2" deep.  In general we found that at any given depth, the small spout yielded approximately 80% the amount of sap as a standard-sized spout.  Sap yield was also strongly related to depth of taphole, with deeper tapholes producing slightly more sap.  Taphole closure was considerably faster for the small diameter spouts than the standard spouts.

  In order to examine the effects of spout size on sap yield under vacuum conditions, we built a number of vacuum chambers.  These chambers were made of clear plexiglass and held approximately 2.5 gallons of sap.  A vacuum line ran into a T-fitting at the bottom.  In normal operation, the line ran to the top to draw a vacuum on the chamber.  A drop line with the appropriate sized spout (normal or small) was connected to the top of the chamber.  Sap would flow from the tree and collect in the bottom of the chamber.  Sap depth was measured using a meter stick and converted to volume.  We collected sap from both small trees (4.5-11" diameter) and large trees (> 20" diameter).  At the end of the season, sap volumes were totaled.  Because different sized trees normally yield varying amounts of sap, a correction factor was calculated for the small trees based upon tree diameter.  This allowed us to calculated a predicted sap production for each tree which was then compared to the actual volume collected.

In all cases in 1999, whether gravity or vacuum, for both big and small trees, the small spouts yielded approximately the same amount of sap as the normal sized spouts. The graph on the right shows the amount of sap recovered compared to the amount produced by the normal sized spout.  In most cases, the small spouts yielded slightly (but not significantly) more sap than the standard spout.  Be aware that the numbers shown in this graph are percentages rather than actual amounts of sap. As you would expect, trees on vacuum yielded more sap than those on gravity, and large trees produced greater quantities of sap than small trees. It has been suggested that small spouts run longer at the end of the season because of less taphole contamination and drying out.  Because our test system was connected to the production bush, we were unable to evaluate this.

In addition to yielding approximately the same amount of sap, smaller spouts produce much less damage to the tree.  We evaluated this by dissecting twelve trees used in the 1998 study.  We started by cutting the trees approximately 3 ft above and below the taphole.  Starting at the taphole, we cut the tree into 4 cm sections until we could no longer see any signs of decay associated with the experimental tap.  The depth and width of damage was measured for each wood section using digital calipers, and the volume of damaged wood calculated.  Our results indicated that the small spouts produce only 1/2 - 2/3 as much damage as the standard sized spout (when placed at the same depth).

Upcoming research will focus on continued measurements of sap yields and damage.  We expect to begin developing guidelines for the new small spouts within the next year or two as more information becomes available.  Until that time, we recommend that sugar makers who start to use these new small spouts continue to use the current tapping guidelines (1 tap for a 12-18" tree, 2 taps for trees > 18").

For further information about this or other research at the Proctor Maple Research Center,
contact Dr. Tim Perkins at (802) 899-9926 or  tperkins@zoo.uvm.edu

Acknowledgements

This research was funded in part by the North American Maple Syrup Council/International Maple Syrup Institute and the Chittenden County Maple Sugar Maker's Association.  The technical assistance and advice of Tim Wilmot, Sumner Williams, Brian Stowe, and Mark Isslehardt is acknowledged with thanks.