Your post: Low brix + fuzzy line = low minerals but ripe (with NPN) ?
Low brix + straight line = low minerals and unripe (No NPN) ?
So are you saying all straight line readings (even when brix is high) means there is presence of NPN?
"ALL" straight Line readings may be indicative of extra Nitrogen, but High Brix readings may not be as subject to having NPN as the Low Brix readings !
Also you may have NPN which is not Potassium Nitrate, but when you have Potassium Nitrate as the problem, this is "WORST" !
The NPN is when the Nitrogen is not able to form a Complete Amino Acid Complex, and thus it may be Nitrogen of it's self or Nitrogen bound with Potassium or Nitrogen bound with some other ingredients partially !
But the "WORST" NPN is when the Nitrogen is bound with the Potassium making Potassium Nitrate !
And in the case which Givati was talking about where the fruit was a 24 Brix, the question remains to be answered about how much higher Brix should the fruit have been , if it was of Top Quality ?
I do not know of this fruit, because I have never tested one which was of Top Quality, so I may not be able to say at this point !
But because he said it tasted sour or such and did not taste as sweet as they normally tasted, then this would indicate it was not ripe which would automatically indicate a presence of NPN, and when he said he was able to correct the problem with the use of taking some Baking soda, then this is indicating that the problem may have been from too much Potassium Nitrate, because the Baking Soda would have provided extra Sodium to Balance out the excess of Potassium, "IF" that was the case !
I am not for sure about this, but with what info he provided, this makes the most Common Sense, and without testing the fruit one may not know for sure !
But my guess is that a ripe sharon fruit may have a much higher Brix reading than 24 Brix for it to be of Top Quality, which may mean that the 24 Brix, while it may seem high to some other foods, may within this fruit be of Poor Quality !
For you must compare the Brix within each of the Line of foods which you are testing to determine the Quality of that food !
It may be like comparing Raisans to white potatoes, with the rasians needing to read above 80 Brix and the white potatoes reading below 10 Brix ?
Just because one food may test higher than another food may not mean that it is Better, for you must compare it to it's self !
For "ALL" fruits should test higher than "ALL" vegetables, but this does not mean that the fruits are better to eat, it just means that they must have a higher ratio of Natural Sugars to go along with the Alkaline Minerals in order to make them a Complete Complexed food !
And the sharon fruit, just by the type of food it is may indicate that it should have a higher Brix reading and also may indicate that it may be higher in Potassium !
Because it naturally has thicker leaves and other things of the plant which are indicative of this ability to have higher potassium in the fruit !
There are reference to it naturally growing better near the ocean area where it may recieve salt from the ocean breeze, which may be indicative of more Sodium to Balance out the Potassium in the fruit, and if it is not grown under these conditions, then the fruit may become too high in it's Potassium in ratio to it's Sodium ?
I do not know for sure about this because I have not worked with this fruit before, but this may make the most Common Sense, with the other knowns about Plants growth patterns and needs !
Smile Tis your choice.