Every now and then, you'll bite into the end piece of a perfectly good cucumber only to get an unwelcome bitter and acrid taste. This happened to me for years, no matter how carefully I selected my cukes, although I generally had better luck with ones I got from local growers and the farmer's market.
Oregon State explains the culprit is an organic compound called cucurbitacin, which tends to concentrate in the leaves, stems, and roots. However, it can travel to the fruit itself, but is more likely to be found at the stem end for just that reason. It rarely moves toward the center of the fruit.
Purdue University points out that stressors like lack of water or excessive heat can cause cucumbers to produce more bitterness. Most places recommend peeling cucumbers of their dark green skin, since other than the stem end, that's where cucurbitacin is most likely to gather.
However, most of the nutrients in cucumbers are concentrated in the skin and the seeds. Plus, I hate losing the rich color and crisp snap the skin provides. So how else can we rid cucumbers of their bitterness without sacrificing the skin? Thankfully, there's an old trick I learned from my Indian friend's mom to remove the bitterness from cucumbers, and it's super easy.
First, wash your cucumbers thoroughly. Then cut a small piece off from both the stem and blossom ends. I usually try and make the piece no larger than about half an inch.
Next, place the cut piece back on the cucumber and start rubbing the flat ends together.
Pretty soon, a white foamy substance will appear. Keep doing this for a minute or two until the cucumber stops producing fresh foam.
Then repeat on the other end. Rinse it off, and the cucumber is ready to eat. Watch the complete how-to video below from YouTuber etriliun to see this process in action.
I'm not really sure why this works. The video above speculates that the action draws out the curcurbitacins. Others say it's just an old folk tale with no basis in science. All I know is that I've never eaten a bitter cucumber when I've remembered to perform this little trick, but I've bitten into many an unpleasant one when I haven't.