Ice crystals occur in any homemade ice cream when there is too much water in the ice cream mixture. While making these recipes I recommend using whipping cream or heavy cream and mangoes which yield a thick pulp when blended. If the mangoes are very juicy, watery, the pulp will be runny and watery resulting in the formation of ice crystals. Also remember to seal or cover your ice cream bowl or box securely and tightly, so that ice crystals are not formed.