Large ice crystals in frozen food product are often an indication that the food product has undergone:

Large ice crystals in frozen food product are often an indication that the food product has undergone: slow and uneven freezing. Because the food molecules cannot form a six-sided snowflake before the freeze is complete, Ice crystals will not form during more rapid freezing. The slower the freezing the larger and less manageable ice crystals result will be made that can cause food damage. Ice crystals can form if the product is not dried completely like in the case of fruits and vegetables.