levain not doubling and loaf spreading out before and during baking
Hello, this is my first post-I have been lurking on the site for a while and enjoying everyone else's contributions!
So I am having issues with my sourdough...
I have a starter which is about 2 months old, a wheat starter which is 100% hydration. My routine is: I keep the starter in the fridge, and take it out the day before I want to bake: from this pot I take 15g of starter and mix it with 50g of water and 50g of flour to make the levain. I then re-feed the mother starter with 7g of water and 7g of flour and put it back in the fridge (same as I have taken out). The levain is left out overnight for about 12/15 hours. The problem I have is that my levain never really doubles...only once it did (and I am not sure why that time as I didn't do anything differently). it is bubbly, and I do the float test and it usually passes, so I use it even if it isn't doubled in size.
I autolyse 500g of flour and 350 of water for an hour or so, then add the levain, and after 15 minutes I add salt. I then stretch and fold every 30 minutes, four times. Then I leave the dough to rest until I see bubbles on top (but I am never sure when exactly I should shape...online information tells me to extend bulk fermentation for another 2-3 hours but I feel that my dough would overproof if I do that).
I shape, and put in a banneton then refrigerate for 15-24 hours. My fridge is very cold and my loaf doesn't rise at all in there, so I don't think the overproofing happens at that stage, but my last two loaves have turned out really flat- I turn them out of the banneton and when I slash them they spread and don't rise up in the oven, the go outward. I know they aren't right as at the slashing point, the blade drags rather than cutting easily. The crumb inside isn't bad, it isn't dense and still had some big holes.
What am I doing wrong?The one time that (for whatever reason) my levain doubled, the loaf turned out amazing so I assume the issue is with my starter. I follow a no-discard routine as detailed above, so the starter is always in the fridge and fed small quantities every time I take the same amount out to build the levain.
Any advice is much appreciated.