How to grow decent mooli/white radish/daikon

We grow white radish every year, just to have something fresh to gnaw on throughout the autumn. However, I find that about half of them don't taste good. The other half I could eat all in one go!
I can't quite describe the bad ones: they taste too earthy? There's something missing. The trouble is, you can't see it until you taste one.
I wonder whether other people have the same phenomenon. What might cause it?
Do people grow them at all? They are so easy: we always have trouble with the little red radishes, but never with the white ones - nor the black ones for that matter, which follow up and without which I could not get through the winter!
I would like to hear other people's experience.
Thanks - love Annemieke.