That's the point of this post. To verify that temperature.
I've been propagating a starter made by Silverton's procedure that was given to me by a friend (thanks Gary) and am putting it to use to make a sourdough boule (900 g before baking; starter = 250 g, water = 250 g, unbleached white flour = 400 g, salt = 9 g).
1. Dough mixed 13 minutes in my bread machine.
2. First rise, ca. 75F, 2.5 hours.
3. Rest, 30 minutes,
4. Shape into a boule and tossed into the fridge for 10 hours (reached 39F).
5. Removed couche from fridge and let warm covered with moistened muslin towel (still with thermometer stuck in the middle of the dough), 39F @ 7 am -> 61F @ 10 am. Pretty amazing. My house was approx 73F in the kitchen and the warming to 62F internal occured at about the time Silverton suggested. Don't know why I never measured this before. Also noteworthy, the final loaf had grown to at least 2x volume. Tough to tell with a boule. Anyway, finally, into the oven.
6. Docked with my usual 4 score pattern and baked in thoroughly pre-heated oven (450F) for 40 minutes on clay tiles with steam shot. Good oven spring in the first 10 minutes.
7. Final loaf = 727 g (20% moisture loss). Let it cool and ate. Pics posted later. It was ok but I still like my poolish method a bit better.
There's a couple things I did different than the Silverton recipe. I didn't use wheat germ, I used a greater fraction of starter and a couple other smaller things. I think I did finally bake it at the right time after retarding the loaf. All things seemed to be consistent (time to warm up, internal temp and volume increase seemed to coincide with the queue to bake). The loaf tasted great but was a little low in terms of oven spring and overall volume. The crumb was quite nice but I wanted greater volume. Maybe the wheat germ was more significant than I thought.
Petra gave me some great information during this recent quest. She pointed me to a discussion and example of someone else who did the same prep (better/different results than mine). Some people feel retarding at 40F is very different than retarding at 50F. At 50F, the bread rises where at 40F it doesn't and just rises when it warms up.??
Next time, I think I'll try some wheat germ. I'm also going to be sampling the loaf over the next few days. Great breads stay good for a few days (in my opinion). Crappy ones look great and taste mediocre for a day and then suck the second day. I read somewhere Poilane believed his mega boules would be perfect by the fourth day!