Preventing spread and getting a good bounce with a mixed rye-wheat bread

Mixed rye-wheat sourdough load with a good bounce

This ever happened to you? I had a break in baking my sourdough loaves over Christmas. The next loaves I set up in the new year all seemed to have a more plastic dough. it spread more during the final rise. When slashed and in the oven, it hardly rose, coming out of the oven like a slightly thicker discus. I tried again. Same result.

I checked through my method line by line. There was one small difference. I'd kept the last rise in a large but closed container to stop the dough drying out too much over the usual three to four hour rise. Before Christmas, I'd covered the floured dough ball with a tea towel.

The third time, I kept the last rise under a tea towel. The dough rose and spread less. The outer surface had formed a slightly drier skin, which resisted the expansion, leading to a more domed loaf. I cut a cross with a sharp knife as previously, to an inch depth and almost to the base the dough was on.

This time, the large bounce occurred within the first 10 minutes  of baking and continued slightly till the end of the bake.

Covering the floured dough with a tea towel prevented the dough from drying out too much. The the less flexible thin skin formed on the surface maintained the loaf's shape and also, I suspect, put the gas bubbles formed in the dough under a slight pressure. After slashing and placing in the oven, the heat caused the rapid controlled expansion which was helped by the cuts exposing the interior, still very moist and flexible, dough