This invention describes the use of mutarotase (also known as aldose-1-epimerase) in a process for carbohydrate crystallization. Preferably the carbohydrate is a reducing sugar, more preferably the carbohydrate is lactose. The mutarotase can be obtained from an organism, preferably a micro-organism, more preferably from a fungus, even more preferably from a fungus of the genus Aspergillus, most preferably from Aspergillus niger. Carbohydrate crystallization can be performed from a pure, partly purified or a crude solution of carbohydrate. In general, carbohydrates are first concentrated into a supersaturated solution, after which temperature decreases and optional seeding with carbohydrate crystals initiate crystallization. Mutarotase is preferably added before or during the crystallization process.