SPECIFIC GRAVITY DETERMINATION WITH A UNIVERSAL TESTING MACHINE

Abstract

SUMMARY —A rapid, precise technique for determining specific gravity of fruits and vegetables was developed. The method utilized a universal testing machine. The effects of crosshead speed, choice of standard density fluid and weight measurements were studied and optimized. A standard sphere of known volume and weight was used to compare this method with other techniques now used. In addition to using the standard sphere, tomatoes were studied to evaluate the efficiency of this method. Calculation of specific gravity involved determining fruit volume and weight. Other volume measurement techniques investigated proved inaccurate or too time‐consuming. An Instron universal testing machine was used in measuring the buoyancy force of a fruit submerged in a standard density fluid. The buoyancy force is directly related to the fruit volume. Error analysis showed relatively low sensitivity to errors in weight measurement, but was influenced mainly by errors in determining the fluid density. This error was minimized by use of high‐density fluids; thus, saturated salt brines and high‐density organic fluids were used for the experimental work.