Hi there, I'm hoping someone wise will know the answer to my little problem.

I've just taken my third sourdough out of the oven. Tastes great - all three have. Good lot of bubbles. Nice crust. All great except I don't seem to get a very good 'oven spring' - the bread is practically the same as when I put it in (apart from 'oven spread'. The result is just flat rather than boule.

I cook in a 210oC preheated fan oven. I slash the top. Proving time 6 hours (straight from fridge) in a 19oC house. I stretch and fold the dough (70%+ hydration) four times. Starter is nice and bubbly. Hmmmm.

Help!