When You Should Avoid Putting Softened Butter Back In The Fridge
So, you've softened too much butter for your latest light and airy Chantilly cake with berries. Now what? You could leave it out, since few things are as frustrating as trying to spread cold butter on toast, or you could just toss it back in the fridge. No big deal, right? Well, yes and no.
Butter, at its core, is an emulsion of fat, water, milk solids, and occasionally salt. As butter softens and melts, the chemical structure begins to change. When it re-hardens, its texture can become grainy and unsuitable for creaming with sugar — a key step to fluffy cakes and soft cookies. Once this happens, the air that's then incorporated via the creaming process won't be as stable due to this structural change, and you risk your cakes not rising properly or frosting being too loose. Bakes that contain leavening agents like baking powder or baking soda rely on the creation of little air bubbles to capture the gasses they release. Better, structurally sound, aerated butter equates to better baked goods.
How to tell your butter is softened and how to save it if it's too soft
The goal when softening butter is to simply bring it to room temperature. However, not everyone's thermostat is set to the same number. Outside of leaving it on the counter and just hoping for the best after a few hours, a good rule of thumb is to use your thumb to test the texture. As you press into it, you want it to feel akin to soft clay. Look for an indent from your thumb, and check that the overall stick doesn't look too greasy. If it hasn't gotten to this point and you've decided against baking with it that day, pop it back in the fridge and you'll be safe from structural harm.
If you've slightly over-softened your butter, then try Carla Hall's simple hack to rescue it: Put it in some flour and avoiding touching it. If the butter is too far gone, like it's one warm breath away from a vaguely congealed melty mess, then throwing it back in the fridge to be used for non-creaming culinary needs is perfectly fine. Over-softened butter that's been re-refrigerated still has plenty of other uses. A couple options would be melting it down for pie crusts, drizzling it over popcorn, or re-softening it for spreading on toast, on a warm slice of easy-peasy three ingredient banana bread, or on some cloud-like buttermilk pancakes.