The window-pane test in bread-making
Behind this mysterious name lies a very physical phenomenon: when dough is kneaded, the gluten in the flour forms a structure, like a kind of net, which holds the dough together. This gluten network gives the dough its elasticity and traps the C02 formed during fermentation to create the “bubbles” which will become the open spaces in the bread.
If you stretch well-kneaded dough, the gluten network will prevent it breaking immediately, so it is possible to stretch it out very thinly, indicating that the gluten network is properly developed.
So, the test is very simple: if the membrane is there, the dough has been kneaded long enough. If not, continue kneading.
Now, of course, we need to know how to check whether the membrane is there or not.
To do this, stop kneading and take a small piece of dough, about the size of a walnut. Stretch this out gently: if the dough tears easily, the membrane is not yet developed and you will need to continue kneading, like in this photo:
If, on the contrary, the dough does not tear, but can be stretched out into a thin, translucent membrane, you can stop kneading. This is shown here:
Here ios a small video to show you the gesture and the result:
To sum up :The presence or absence of the translucent membrane is the best indicator of whether bread dough is sufficiently kneaded or not.
But not all dough in baking is the same: this membrane should be looked for in bread dough as a sign of elasticity. However, for tart pastry, it is quite the contrary: we don’t want the dough to be stretchy and develop the gluten membrane. So, for pastry, the dough should be kneaded as little as possible.