Reader Jane happened to mention dough stretching in the comment fields of the below post on sourdough starters. The comment elicited several follow-up questions about dough stretching and yeast in general, which I thought I’d answer here on the main page instead of in the comment fields.
So let’s get down to business: what is dough stretching? It’s pretty much as it sounds — a process by which you gently tug bread dough into an elongated shape as it rises, and then fold it or roll it back up into a lump and let it rise some more. You generally start the stretching at about the mid-point of the initial rise (after mixing your bread dough, but before you shape the loaf).
Several readers have written in to ask this question, and it’s a good one. Now that home bakers are so widely using bread starters and preferments, why bother with the packaged stuff since it delivers inferior flavor even if the rise is faster? I can think of a few reasons.
Concentrated yeast cultures — brewer’s yeast or packaged yeast — work faster and so create lighter, fluffier breads. Bakers, especially those living in cities, have known this for centuries. These urban dwellers are people who’ve historically had access to brewery leftovers as well as more finely-milled flours. That’s why in general their breads tended to be more toothsome (at least when they weren’t full of sawdust and mice) if not the most flavorful.
Being a living thing, yeast has needs if it’s going to survive in the kitchen or anywhere else. Obviously it needs food (simple sugars) and water. Beyond that it has temperature requirements. It grows and produces CO2 most prodigiously at about 92 degrees Fahrenheit. It slows to the point of dormancy at 40 degrees and goes completely dormant below the freezing point of water. If it’s frozen for long, some of its population dies, about 10% per month. Similarly, yeast activity starts to slow down when the temperature gets over about 100 degrees Fahrenheit and stops completely at 135 degrees, at which point it dies.