stretch and fold magic
Two Glues and a Foam
The general descriptions of what happens when a stretch and fold is carried out are usually misleading or wrong. It is nothing short of magic to explain dough strengthening in terms of gluten strengthening and strands of gluten being straightened or surface tension effects. The real fun science is missing, everywhere, even in the bread makers’ books. That is a shame because it is hard to improve on magic, unless you have a better spells book and I have not seen any.
All bubbles produce a restoring force when their shapes are distorted, so when you poke a finger against the surface of a balloon you feel this force as your finger pushes in, take away your finger and the balloon surface goes back to the original shape. We use this restoring force when a stretch and fold is done on dough foam.
The problem is how to describe something that is more like a liquid than a solid, is extendible and elastic, and grows into a foam that can support its own weight. What is done to the foam makes the dough stronger. The proofing/proving is about waiting for the bubbles of the foam to grow large enough and round enough to support the weight and shape of the dough and the tool to use is the stretch and fold technique.
You can feel the restoring force produced by the bending distorted bubbles when you do your stretch and folds. It is not noticeable at first, the bubbles are too small, but as they grow each stretch and fold is harder to make to distort the bubbles against the viscous gluten. The gas in a bubble pushes against the gluten and tries to keep it’s shape nearly round. Nearly round bubbles packed together keep the shape of their gluten foam better than any other bubble shape and the bigger the bubbles the better because that spreads the dough weight over a bigger surface area and so makes it easier to hold up.
At the end of the knead the two important glues in the gluten are ready for use. The glue that holds everything together is working throughout the dough and keeps working all the time. The other glue that only works for about 25 minutes is also working. Pull a lump of new dough into a log and put it on the work surface. It shrinks a bit, that is the 25 minute glue in action. The fact that the shrunken log stays as a shrunken log is due to the first glue. Remaking the 25 minute glue just means stretching/bending the dough, what you do when you stretch and fold.
As the newly kneaded dough starts to prove/proof the foam starts to grow. But the dough is sinking into a flattening blob. So you fold it back on itself and stretch it a bit in the process and pin it down on the dough still sticking to the work surface to get it back to a useable lump, an obvious natural movement.
That short life glue is essential for sticking/pinning your fold down onto the remaining dough and leaving a small amount of tension. This helps to support the new dough shape whilst the newly distorted bubbles have time to reshape to their normal ‘round’ shape in the viscous gluten. The dough gets stronger than it was and keeps its shape better because the bubbles have grown a bit and are nearly round. (They are all trying to be round but geometry stacking and gravity mess them up a bit).
The point of the stretch and fold is to reshape the dough using the properties of the foam to make it stronger and hold its shape better each time.. You could say, as you work your dough, ‘mine’s got bigger rounder bubbles than yours’ rather than ‘mine is stronger than yours’...
The glue that holds everything together reaches peak glueiness at the window pane test time. It is all to do with breaking/making of disulphide bonds that cannot be used again. The 25 minute glue uses hydrogen bonds that are electrostatic so make and break as many times as you want. Both types of bonds are between gluten chains etc.
Taken time to pluck up courage. thanks for reading, comments?