Lee and Oberle (41) compared the so-called "'pea" Penecrometens with the 
Magness-Taylor pressure tester obtaining a high correlation of 0.96 = 0.015 
standard error. The penetrometer blades shear a known volume of tissue and 
the instrument expresses values in pounds force per square inch. The pene- 
trometer values decrease with advancing maturity to a point where a flattening 
off or no change in reading indicates optimum maturity. 
Lee's data show that a prediction of a set penetrometer value for a 
given variety would not be applicable from season to season. 
Caldwell, Culpepper, and Demaree (5) determined the relationship of 
different pressure test groups (firmness of raw product measured by Magness- 
Taylor pressure tester) with color, flavor, and particularly disintegration of 
frozen apple packs. Disintegration increased rapidly with decreasing firmness. 
Pflug, Joffe, and Nicholas (61) constructed a mechanically driven 
pressure tester incorporating a force versus displacement recording system. 
With vertical*placement and a controlled system, greater accuracy could be 
maintained and human variability diminished. 
Nicholas (56) showed that firmness measurements of several materials, 
including apples, are different depending on the individual making the measure- 
ment. Comparisons of the variance of the force readings obtained by individuals 
using a fruit pressure tester with the variance obtained by a mechanical 
recording pressure tester show discrepancies depending on the product tested, 
Decker et al, (15) modified the shear-press for electrical indicating 
and recording. Work curves for fruit and vegetable products could then be 
developed that would provide more complete information about the product. 
Woodmansee, McClendon, and Somers (92) correlated pressure test readings 
of Stayman apples with three greatly different stages of maturity of freshly 
harvested fruit. 
Wiley and Thompson (90) used the shear-press to good advantage on apples 
to predict canned apple slice firmness and wholeness. They found that readings 
within a 300- to 400-pound range gave slices of most ideal firmness and whole- 
ness. Ideal firmness was found in early harvested apples which had ripened 
slightly in storage. 
Shallenberger et al. (7/0) reported that as harvest date was delayed, 
color and flavor improved and texture became firmer in canned apple slices. 
The relationship between the alcohol insoluble solids to total solids ratio 
and the increasing firmness of slices with increasing blanch temperature 
suggests the basis for establishing a raw-apple objective index of slice 
firmness, 
Mohsenin, Goehlich, and Tukey (55) found that a yield point and rupture 
point determined by a new compression tester were more definitive of force 
reference than the 1/4 inch line of the Magness-Taylor tester. They also found 
that as fruits mature, both the deformation curve and energy curve drop more 
rapidly than the stress curve during the harvest period. The compression 
tester seemed to be a better instrument for determining maturity and ripeness 
of apples, since several physical properties of the fruit can be measured and 
calculated at definite reference points. 
Color 
The color of apple fruit is often the principal criterion for acceptance 
by the consumer. The Federal grades assign considerable import to color, 
specifying that as high as 66 percent of the total surface area of the solid 
