Making the test : Having calibrated the pressure tester and care - 

 fully chosen a~sample, how should you test the fruits? First, you 

 shouldrecognize that the fruit is not of uniform firmness. Gener- 

 ally, the blush side is firmer than the green side. This differ- 

 ence may be as much as 1 lb of pressure. Therefore, either consis- 

 tently test the blush side, knowing it is firmer, or the green side, 

 knowing it is softer, or else test both the blush and the green sides 

 and average the readings. 



Since the skin badly distorts a pressure test on an apple, it 

 must be removed from the area to be tested. The depth of the cut 

 removing this skin influences the reading: the deeper the cut, the 

 higher the reading. Dr. Robert Hardenburg suggests use of a potato 

 peeler (stainless steel to avoid rusting) for quick, shallow, con- 

 sistent cuts. These cuts should be made at a point half way between 

 the stem and calyx ends of the fruit. Never test a bruised area. 



For testing, the fruit should be placed on a hard surface (e.g., 

 table top) rather than being hand-held. The plunger should be in- 

 serted to the line inscribed on the plunger . Testing only to the 

 "yield point" of the fruit tissue (i.e. , when it "gives") produces 

 an erroneously low reading, and going beyond the line gives a high 

 reading. However, the most critical feature of testing is the speed 

 of applying the force . The faster you apply the pressure, the higher 

 will be the reading. The proper speed is about 2 seconds, and to 

 regulate your speed it is suggested that you say to yourself, "1001, 

 1002, as you insert the plunger into the fruit. This may sound 

 childish, but it is extremely critical as can be seen simply by ap- 

 plying force at different speeds during calibration. The user needs 

 to frequently check himself during testing to make sure he is test- 

 ing at the proper speed. Applying pressure too fast is probably the 

 greatest source of false readings by users of the pressure tester . 



Having tested the fruit, how do you read the scale? Some read 

 it to the nearest whole lb., others to the nearest 1/2 lb., and some 

 may even read to the nearest 1/10 lb. It seems clear that reading 

 to the nearest 1/2 lb. is sufficient, and if your sample size is 

 reasonably large, the nearest 1 lb. is satisfactory. Again m.y prefer- 

 ence is to the nearest 1/2 lb. 



With an accurate instrument, careful sampling, and precise 

 testing, you should obtain a quite accurate firmness measurement 

 of the fruits. But this accurate measurement still may not truly 

 represent the "condition" of the apple. Some sources of error are 

 the following. 



A. Nitrogen (N) level of the fruit: Increasing the N level in 

 apples may reduce firmness of apples more than it affects 

 postharvest "condition" of them if the apples were at the 

 threshold of N-deficiency before treatment. Thus, you may 

 misjudge "condition" by comparing lots of widely varying 

 N levels. 



