What you are looking at is "Towering Cu", they usually begin their life from Cu cloud (cauliflower as you put it) then either disapate into nothing or, more often than not, are the precurser for CBs.
Unless you are a very experenced glider pilot and looking for serious thermals, if you see them - avoid them.
They have the same, albeit reduced, qualities of a CB and can make your flying experience an unpleasant one.
There will of course, be the bold, but not old, flyers who know everything and will disagree, but their advice is worth ignoring.