What is freeze ripening of date?

The dates which are on the khalal stage are picked and cleaned thoroughly to remove the dirt. A solution of lemon juice and water is prepared and the dates area soaked in it for 10 minutes as an attempt to pre-treat the dates. The solution is drained and the dates are wrapped in freezer paper or placed in freezer bags. They are freezed at a temperature of -64 to -122°F for 24 hours so that they reach the rutab stage. This process is call freeze drying.