Natural Vacuum and the flow of maple sap

Abstract

In 1967, Blum (1) reported that 43 percent more sap was obtained from closed tubing installations on slopes than from open or vented tubing. He associated this increase with the natural vacuum created in the closed tubing. Gains in sap yield from natural vacuum are especially important, since the collection of sap is the most costly and least profitable phase of making maple sirup. Moreover, sap costs for a tubing network are mostly fixed costs; in- creased sap flow from natural vacuum represents added profit with little or no added cost. Recently, Laing et al. (6) showed that sap produced with high vacuum differed little in chemical composition from sap produced without vacuum; both yielded sirup of comparable high quality.