A Big(a) Controversy
I've made the same or similar biga based loaves since and they've never been as good - in terms of crust, ears, loft and crumb. What I've come to realise is that in my original loaf I made the biga the wrong way After that I read some more about bigas and started making the biga the right way
I define the wrong way as mixing the biga to a single cohesive lump (but without gluten development) and storing it as such. This can be done, even at 45% hydration, at least in a spiral mixer.
I define the right way as mixing for a shorter time, just to get those barely hydrated shreds, often with some dry flour left.
After mixing I stored the biga for 24 hours at 11-12C prior to use, so somewhat colder than a normal biga, which would be 16-18C.
In conclusion I think that mixing the biga "incorrectly" actually gives me better results than the proper method and I will continue to make it this way. Here's a picture of todays loaf: