FRUIT PRESSURE TESTERS 5 



to use a small plunger so that less force was required. The United 

 States Department of Agriculture tester can be held at the end, and 

 this permits a steady application of a considerably greater pressure. 

 With the %6-mch plunger used by Blake and Davidson (10) the 

 extremes of pressure test were 10 pounds for green-shipping ripe and 

 1 pound for soft ripe, whereas for the % 6 -inch plunger they gave 

 corresponding extremes of 20 pounds and 2 pounds. They stated 

 that plungers of either size give dependable results. The much 

 greater range in pressure test (18 pounds compared with 9) obtained 

 with the % 6-inch plunger should make this more accurate and sensitive. 

 From the foregoing discussion it is apparent that a rather uniform 

 method of testing apples and pears has been adopted but that the 

 method of testing the firmness of peaches has varied greatly in the 

 number of tests per peach, the points at which the tests were made, 

 the size of the plunger, and as to whether the tests were made on the 

 pared or unpared surface. Blake and Davidson (10) deplored this 

 lack of uniformity, yet added to it by adopting a plunger size differing 

 from that used originally by Magness and Allen (Jj.2) and subsequently 

 by most other investigators (14, 31, 51). For the sake of uniformity 

 it is suggested that the following method of testing peaches be adopted: 



(1) That a plunger % 6 of an inch in diameter with a penetration of ;K 6 of an 

 inch be used. This size has been most generally used and does not give readings 

 that are too high when used with the United States Department of Agriculture 

 tester. 



(2) That 2 tests be made on each peach; 1 on each pared cheek. Making 10 

 or 12 tests on each peach greatly increases the time and labor required, and as 

 the average of 12 tests, as reported by Blake and Davidson (10), did not differ 

 appreciably from the average of the 2 tests, 1 on each cheek, it would seem unneces- 

 sary to make so many tests. Although ripening may progress more rapidly at 

 the suture or other points, it is likely that tests on the cheeks would give an 

 equally satisfactory measure of maturity or ripeness. After making tests at 

 various points, Coe (14) concluded that tests on the cheeks were more satisfactory 

 than those on the suture. As with apples and pears, the firmness of the flesh 

 rather than the texture or toughness of the skin should be the best measure of 

 maturity or ripeness, and therefore the skin should be removed before making 

 a test. 



A random sample of 20 to 30 fruits is generally used for pressure 

 testing. In fairly uniform lots of apples and pears the mean of such 

 a sample will usually have a standard error of about 0.1 to 0.2 of a 

 pound; this is sufficiently accurate for nearly all purposes. As peaches 

 often vary more than apples or pears, at least 30 fruits to the sample 

 would perhaps be desirable. 



In making a test the skin is removed at the points to be tested by 

 slicing off pieces of somewhat greater diameter than that of the plunger 

 point. The fruit is held in one hand, and with the other hand the 

 plunger point is directed squarely against the cut surface, and the 

 pressure is gradually increased until the plunger penetrates to the 

 mark on its side. When the mark is reached, the pressure is released 

 and the reading indicated by the slide is recorded. The slide is then 

 returned to the zero position, and the next test is made. If the fruit 

 is hard, a steady application of the force can be obtained by holding 

 the fruit against a wall or other convenient surface and bearing the 

 weight of the body against the opposite end of the instrument or the 

 hand holding it. 



