Brie cheese turning white when refrigerated overnight is a normal and natural process called "blooming." Brie cheese is a soft, creamy cheese with a white rind made from Penicillium candidum, a type of mold. The rind is an essential part of Brie's character and flavor.
When Brie cheese is left at room temperature or slightly warmer conditions, the mold on the surface becomes more active and grows, giving the cheese its characteristic white appearance. This mold is responsible for breaking down the cheese's proteins and fats, which contributes to the cheese's soft, runny texture and distinct flavor.
However, when Brie cheese is refrigerated, the lower temperature slows down the activity of the mold. As a result, the mold growth decreases, and the rind may turn paler or white during this cooler storage period.
Despite the change in color, the cheese is still perfectly safe to eat. The flavor and texture of Brie will remain largely unaffected by the blooming process, and once the cheese is taken out of the refrigerator and allowed to come to room temperature again, the mold will become more active, and the rind may regain its typical white appearance.
If you enjoy the full bloomed look, you can let the Brie sit at room temperature for a while before serving to encourage the mold to grow and the rind to become more pronounced. Just remember to store Brie cheese properly in the refrigerator when not serving to prevent it from spoiling or becoming too runny.