If they get too old on the vine they get bitter. Also, a cucumber is about 80% or more water so pesticides and other chemicals can leave a residual taste.
Sometimes I've had a few plants that produced nothing but nasty-tasting cucumbers. Mostly those Burpee seed packages that can't be trusted. I pull those up and feed them to the goats, who don't seem to mind the bitter taste.
My extension vegetable specialist told me that if you water frequently, the roots never seem to go deeper into the soil, and when that happens, the fruits get bitter with even the slightest bit of dryness. So the idea is not to water but once a week, and/or only if there isn't any rain for more than a week.
This can also happen with squash (zucchini). When I was watering every other day, they came out so bitter one year that you had to spit it out. This year I've got them on black plastic which helps retain the moisture, among other things, and they are fine. I think I watered once or twice when it was really dry, but did it thoroughly.
A forum community dedicated to living sustainably and self sufficiently. Come join the discussion about livestock, farming, gardening, DIY projects, hobbies, recipes, styles, reviews, accessories, classifieds, and more!