The causes of external BER and internal BER are very different.
I tried to find to find the article that Mike Dunton at Victory Seeds asked me to write
Well I found it,at least the first version and amended
it to discuss internal BER as I recall
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http://www.webgrower.com/information/carolyn_ber.html
Internal BER occurs when not enough calcium makes it the blossom end where one can see the typical external symptoms.
One can't see internal BER until the fruits are cut open.
Maybe this might help as well
https://www.google.com/search?q=inte...&bih=788&dpr=1
Carolyn, hoping that the links work since I can't see that when previewing a post.Mike was generous in saying I'd grown 1000 tomato varieties but that's up to about 5,000 by now.