Hi there, Nicole! Most batters and dough can be overmixed regardless of if they have xanthan gum in them. Over-creaming butter and sugar in a cake recipe can make for dense, gluey streaks in the cake as well as "tunneling." Tunneling is when you cut a cake or muffin and there are lots of larger air pockets or tunnels throughout the structure, this usually happens while mixing in the flour in a recipe. We hope this can help! 

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