What causes cucumbers to become extremely bitter, but only at the stem end?
Hmmmm. lack of water. just a guess
Look what I found...http://chronicle.augusta.com/life/home/gardening/2011-07-07/bitter-taste-cucumbers-can-be-removed
I have heard bitter cucumbers come from inconsistent watering.
It could also be the variety. Some are more temperamental than others. I was growing a variety a few years back (forget the name). The first wave of cucumbers were always bitter, then they mellowed as the season went on. I tried a new variety, Corinto, and have not had that problem since.
See info at link -
Here is a link that might be useful: bitterness explained
I grow "County Fair" cucs, which lack the bitter gene. (which is why it doesn't attract cucumber beetles). I wonder what that means in terms of it tasting bitter??
I trialed cukes this year and found 'Telegraph' put out an occasional bitter-beyond-belief cuke.