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 growth 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).
You stretch the dough every half hour or so, maybe two or three times in total, until the dough is ready to be shaped (i.e. where you can really see bubbles when you cut into the mass). If this sounds a little familiar, it’s because stretching is a more refined version of what was once known as “punching down”. Punching down has evolved into stretching because simply de-gassing a dough doesn’t take full advantage of what goes on under the hood of a rising mass of dough.
And what is that? In short: yeast growth. And here we need to back up a bit to talk about yeasts. The first thing to know about yeasts is that they are very, very simple organisms. Which is to say single-celled little critters that have but three jobs: to eat, to excrete and to reproduce. As they carry on in this way they turn simple flour-and-water pastes into lovely light-and-fluffy, hole-filled, ready-to-bake doughs.
Not being a microbiologist I can’t tell how yeast metabolism actually works. What I can say is that yeasts can digest only the simplest of sugars: monosaccharides like glucose and fructose and disaccharides like maltose. In the process of consuming a molecule of some such sugar, a yeast microbe gives up two molecules of alcohol and two molecules of C02. Me, I’d call that a bargain.
But here’s the rub: yeasts can’t move around on their own. Unlike the paramecia that we studied in school — which have little hairs on them called cilia that give them locomotion — yeasts are stationary creatures. When they reproduce, they do so by budding. That is, they grow smaller versions of themselves on their tiny unicellular bodies. And those buds don’t move around either. Which means that if they’re going to do the job we want them to do throughout a mass of bread dough, we have to manually shift them from food supply to food supply. This is why stretching is so important.
Stretching spreads yeast buds through the dough, where they land on new food supplies and create new little little bubbles of carbon dioxide gas. Stretching also has the effect of elongating existing C02 bubbles that have already been created. The overall effect is more and larger bubbles, and ultimately a lighter, hole-filled bread crumb.
And that is what dough stretching is. Thank you readers Jane, Ed, Ted and Christpoh!