They are signs of a little too much nutrients. Although you use a very decent amount, sometimes it happens. For example I never fertilize when the moon is at it's down peak. So there are 5 days in the month. I picked this from a biodynamic moon calendar I found on the web. And it really works, not just feeding wise. I do my waterings, defoliation and topping, harvest according to this. The results in terms of quality are easily noticed.