- 2 - 



Choosing a sample for testing : The user should consciously and care- 

 fully choose the fruits that will be tested, knowing the factors that 

 may influence the readings. 



A. If you are testing in the orchard, it is likely that fruit 

 from the outside of the tree will test firmer than those 

 toward the inside of the tree. 



B. Fruit size is a very important factor. In general, the 

 larger the fruit, the softer it will be. Sometimes a 1/4 

 inch difference in diameter can make a 1 or 2 lb differ- 

 ence in the pressure test! Following years of careful 

 record-keeping. Dr. George Mattus suggests that you not 

 vary more than 1/4 inch in diameter among the fruit you J 

 test. Obviously, some kind of sizing device is therefore ' 

 necessary in choosing a sample. Further, you should test 



a size that is representative of the majority of the crop, 

 and specify the size you are testing. You cannot accurately 

 compare firmness of lots of fruit if you sample 3-inch fruit 

 in one lot and 2-1/4 inch fruit in the other. 



C. The temperature of the fruit can have a small but sometimes 

 significant influence on pressure tests. Firmness tends 



to be slightly less when apples are warm than when they 

 are cold. This is not nearly as important a point as is 

 the size of the fruit, but for maximum accuracy, the user 

 should be consistent about testing either warm fruits or 

 cold fruits. 



D. A very important but controversial question is: How many 

 fruits should you test, and how many times should you test 

 each fruit? Obviously, 1 fruit is not sufficient, and the 

 more fruits you test, the more accurate will be the aver- 

 age pressure reading. But, between these 2 indisputable 

 points there is little agreement. Many people test only 

 once per fruit, but many others test twice -- once on each 

 of the opposite sides (usually blush and green sides). 

 Some people may even test as many as 4 points on an apple. 

 (Is 1 apple tested on 2 opposite sides equal to 2 apples 

 tested on 1 side? Probably not.) How many different fruits 

 should you test? Most people agree that 10 fruits from a 

 given lot is probably minimal for accuracy, but may prefer 

 20 to 25 fruits to reduce error. If only 10 are tested, 

 they should probably each be tested on 2 opposite sides. 



I personally prefer testing 20 apples once on a designated 

 (green or blush) side. The significant point here is, how- 

 ever, that a large enough sample must be tested to overcome 

 the variation within the population of fruits being samp- 

 led. If large variation exists, a large sample size is 

 required. 



