“Room Temperature Butter” Has an Actual Target

Photo by pfctdayelise, CC BY-SA 2.5, via Wikimedia Commons

Creaming butter with sugar isn't just mixing — the sugar crystals cut tiny air pockets into the butter, and those pockets expand in the oven to help leaven cakes and cookies. That only works in a specific window, around 65°F (18°C): cold butter won't cream smoothly and won't trap air, but butter that's gotten too soft or greasy-looking can't hold the air pockets either, and the bake ends up dense either way. If you press a finger into the butter and it leaves an indent without the butter collapsing or looking shiny, it's in the right range — if it's shiny or oily-looking, it's already too warm.