"使结晶为砂糖" can be translated into English as "to crystallize into sugar (or specifically, granulated sugar)".
Here, "crystallize" means to form crystals, and "into sugar" specifies the resulting substance. If you want to emphasize it's granulated sugar (a common form of processed sugar), you can use "granulated sugar" instead of just "sugar".
A more natural and concise expression in everyday contexts might also be: "to form sugar crystals (especially granulated sugar)".