My sense is very strong that you SHOULD NOT! lock it down. I think that will inhibit the development because the yeast need oxygen to reproduce properly, and you won't be able to tell when the dough needs to be punched down because it won't be free to rise until ready for that (unless your crock is very big - but even then I don't think you should cover it tightly. The covering you have now seems fine to me.
I'm letting a sourdough starter raise in an enamel coated 'crock' that has a 'lock down' lid on it. Should/could I 'lock it down' while fermenting/raising, or will the 'gases' it creates be too much? I currently have it open with a plastic wrap covering the top.
This message was edited by snoboard on 1-1-10 @ 10:55 AM