Over-kneading brioche dough results in a tough, dense bread due to excessive gluten development, which makes the dough difficult to shape and reduces its characteristic tenderness.
Brioche dough is enriched with butter and eggs, which naturally inhibit gluten formation. Kneading is essential to develop enough gluten to give the bread structure. However, over-kneading causes the gluten strands to become too tight and elastic. This leads to several problems:
Tough Texture: The excessive gluten makes the baked brioche tough and less tender than it should be. The crumb will be dense and chewy instead of light and airy.
Difficult Shaping: Over-kneaded dough becomes very elastic and resistant to shaping. It will constantly spring back, making it hard to achieve the desired form.
Reduced Volume: While some gluten development is necessary for rise, too much can hinder it. The tight gluten network can restrict the dough's ability to expand fully during proofing and baking, resulting in a smaller loaf.
Dryness: Overworked gluten can also contribute to a drier final product, as it can affect the dough's ability to retain moisture.
Therefore, it's crucial to knead brioche dough just until it's smooth and elastic, but not overly so. The windowpane test can be helpful, but remember that brioche dough will always be a bit more fragile than leaner doughs.
Use a stand mixer for brioche dough. It helps to develop the gluten efficiently without overworking it. Monitor the dough closely and stop kneading as soon as it becomes smooth and elastic, even if it still feels slightly sticky.