Why cookies spread
In the oven, the butter melts first and the dough slumps outward. Then the eggs and flour set and lock in the shape. Cold dough, extra flour or a hotter oven makes the cookie set sooner, so it spreads less.
Sugar loosens the dough
Sugar melts as cookies bake and loosens the dough, so more sugar gives flatter, crisper cookies. Brown sugar holds more water than white sugar, so it gives chewier cookies. Mix the two to balance chewy against crisp.
Test yourself
Questions from the interactive lesson, with the answer and the why.
Your cookies spread into thin crisps. Which change helps most?
Chill the dough for at least 30 minutes. Cold fat melts later, so the dough sets before it spreads.
True or false: Chilled cookie dough spreads more than room-temperature dough.
False. Cold butter melts later, so chilled dough sets before it can spread.
What went wrong? You scoop soft dough onto a baking sheet that's still warm from the last batch. The cookies come out thin and lacy.
Warm dough on a warm tray melted too early. Chill the dough and use a cool tray.
Fill the blank: Cold cookie dough spreads less because the butter takes longer to ___.
Cold cookie dough spreads less because the butter takes longer to melt. Cold butter melts later, so the structure sets first.
You want thick, chewy cookies. Which combination is best?
More brown sugar and chilled dough. Brown sugar holds water for chew, and chilling limits spread.
Chilled vs room temperature cookie dough
Spread or stay thick?
Do the 40-minute experiment