OK, getting closer to the end, I hope. About 28 h have passed since stage 2 (again a change to the original instructions of 24 h) and I took out my bowl of ferment.
Needless to say, there has been intense activity in there.
Stage 3 adds further food to the mixture, so I measured that up first. 400 g strong white flour and 200 g warm water. This is mixed up with 200 g of the ferment from stage 2.
When I removed the cling film, it smelt the same as yesterday - mostly sickly sweet, a bit like cheese and with a hint of alcohol. I scraped off as much as possible of the ferment from the cling film, then measured up 200 g of it and added the previously measured flour and water and mixed it up into a very nice soft dough. In fact, it was tricky to mix with a spoon or a dough scraper, so I ended up mixing it by hand, but still in the bowl. I formed a decent ball, turned the seam side down and covered with a new piece of cling film. In 12 h it will be ready for stage 4, though since that'll be practically in the middle of the night, it'll be a bit longer than 12 h.
The remaining 550 g (approximately) of ferment were not to be thrown away, but mixed with 500 g of white flour. As the instructions stated this is resulted in an extremely dry mixture, which pretty much stayed in crumbles, I didn't manage to get it to hold together like dough. But most of the flour was absorbed. Then, I crumbled this mixture further onto four baking sheets, lined with baking paper and now two of them are baking in the oven at hopefully less than 50 degrees C. The lowest setting on the main oven is "S" for slow cooking and this corresponds to around 100 degrees C, so I've placed a large empty baking tray at the top, then a second one near the bottom to stop the heat and keep it in the upper half, then the tray with the crumbles is on the very floor of the oven.
I've done the same with the secondary oven (grill) - an empty tray on the highest rack, then the crumb sheet on the floor of it. This is what the book recommends. Baking for about 3 h, then whizzing in a food processor and storing in airtight jars for later use. Which I will put to the test in a few weeks' time.
The two trays that are waiting to be oven dried have actually dried pretty nicely already, so won't require as long in the oven. The main worry here is that if the temperature is too high, the ferment will die. In which case I'll have a lot of funny tasting breadcrumbs to use up somehow.
One thing I noticed is that as I was pouring out the ferment, the alcohol aroma got stronger towards the bottom of the ferment, whereas the top was more sickly sweet smelling. I hope this is OK.
So, early tomorrow morning the sourdough will have risen a bit.