17324_Hutch-MSD Jun05.qxd (Page 2)

INTRODUCTION Two factors have major influences on maple sap yields: vacuum level achieved at the taphole and taphole drying. Vacuum controls sap yield by increasing the pressure differential between the inside of the tree and the inside of the tubing system, resulting in higher sap flows from tapholes than would be found without vacuum (Heiligmann et al. 2006, Chapeskie and Staats 2006, Wilmot et al. 2007). Good vacuum is primarily a matter of proper tubing system design and installation, vacuum pump capability, and the control of leaks. Taphole drying, the slowdown or cessation of sapflow which is typically observed in the second half of each sap flow season, and the factor often responsible for determining the time at which sap flow ends, is a direct result of microbial contamination (Naghski and Willits 1955). It has long been recognized that microbial contamination is strongly related to yield in sap collection systems (Sheneman et al. 1959). A multi-year study at the UVM Proctor Maple Research