fold something in/fold something into something
phrasal verb with fold verb uk/fəʊld/ us/foʊld/
（烹调中）把…调入，拌入
(in cooking) to mix a substance into another substance by turning it gently with a spoon
Fold the egg whites into the cake mixture. 把蛋白调入蛋糕混合物。
Fold in the flour. 拌入面粉。