Galatians 5:9 says a little of what works through the whole batch of dough?

Answer: Leaven

Warning about those who hindered the Galatians, Paul says, "A little leaven works through the whole batch of dough."

“You were running so well. Who has obstructed you from obeying the truth? Such persuasion does not come from the One who calls you. A little leaven works through the whole batch of dough.”— Galatians 5:7-9 (BSB)