How warm must dough be in order to rise?
While making some focaccia this afternoon, my wife said, "sure the house is 'warm'; it'll be fine." One hour later, no rising. It may be worth noting that our house is 66F. So we stuck it in a warm oven and it rose just fine. It turned out fine, I'm just glad we weren't trying to get it done for a meal.
So the question is, how warm does dough need to be to rise properly?
I live in the Northeastern part of New York State in the Adirondacks, near Vermont. I play havoc to get my dough to rise this Winter. I think I'll make the dough before I go to bed and let it rise throughout the night.
Optimal yeast growth happens at around 37 degrees Celsius (98.6 degrees Fahrenheit), but dough will rise at any room temperature. As the temp rises, the yeast becomes more active, which is why you'll sometimes see recipes call over overnight rests in the fridge, where activity slows or stops. Yeast dies at anything above 50 C (122 F).
The important thing is knowing the temperature and, if you're really particular, the humidity in the air around your proof. This information is used for the sake of timing consistency, more than anything else.
I should add that there's really no "proper" temperature to rise. Rise is caused by yeast converting sugars into gas (and alcohol), but a lot of warm rises shoot for about 25 to 30 C. Some people say that a slower, cooler rise makes for a more complexly flavored bread, but that hasn't been my experience with straight doughs. (Older yeasts in starters like levain or sourdough, though, definitely change the flavor.)