How much can you stir different kinds of batter?
I understand the basic principle that stirring batter (or kneading dough) develops the gluten in flour, and that how much you mix any given batter has to do with how much you want the gluten to develop. So, for quick breads like waffles or banana bread you want to stir as little as possible to ensure the most tender result.
I always assumed this rule was true for cakes and other baked goods as well, but then I made a recipe that called for the cake batter to be beaten on high speed for 2 full minutes. It came out moist and tender even with all the beating.
So what's the deal? How long should you beat different kinds of batter? When must you be really careful not to overmix, and when can you mix away? Why would you beat one cake batter on high for 2 minutes, when other cake batters should only be minimally mixed? What are the factors you should take into account if a recipe isn't specific about mixing technique or time?
With cake batter, you beat air into the batter (which is why it's on high for 2 minutes) - also if cake flour is used, it already has a lower protein content.
With quick breads/muffins/etc, you have to fold the ingredients together carefully until JUST combined to not make it tough.
If the recipe doesn't say, I would go with what you're making - if it's a cake being mixed in a mixer, beat until well combined. If it's muffins or pancakes, make sure to not beat. Usually you should aim for somewhere in the middle, because it will tell you if it's one extreme or the other.
In addition, since I've just read Peter Reinhart's Crust and Crumb book (very informative, can't wait to start trying out different types of sponges), you can mix muffins like cake, by first creaming butter and sugar, like a cake, to get a lighter, fluffier result. But, if you're using melted butter or oil, you barely mix, to get that more solid dense loaf.