I grow mine in a
greenhouse and last year I had that problem and was advised that it may be getting too hot for cauliflower, so I "tied up" all the leaves so the center was not even visible, it may help the center to stay cooler. But I don't know how hot you are getting. Below, the caufiflower is on the left, all tied up.
![[Linked Image]](http://i1153.photobucket.com/albums/p506/bobbievcncom/flowersplantsmaytwentytwelve008.jpg)