"Overmixing your dough will result in flatter, crispier cookies," Cowan said. If you overmix, you will end up aerating the dough (adding air) which causes the cookies to rise and then fall, leaving you with flat cookies.

Do cookies become chewy when Overmixed?

You want to make sure to not overmix. I like to stop the mixer right before it's all mixed in, and then finish mixing with a spatula. Overmixing will result in dense, tough cookies because it will create too much gluten (protein in flour that make it chewy and tough).

What happen to your dough if you overbeat it?

Overworked dough can happen when using a stand mixer. Dough will feel “tight” and tough, as the gluten molecules have become damaged, meaning that it won't stretch, only break, when you try to pull or roll it. ... Over kneaded dough can't be fixed and will result in a rock-hard loaf, so be careful with this mistake.