214 MANUAL OF TROPICAL AND SUBTROPICAL FRUITS 



method of artificial ripening has been practiced in most date- 

 growing countries since the time of the earliest written records. 

 Much careful experimentation has been done in this country, 

 first by the Arizona Experiment Station and later by the 

 United States Department of Agriculture. As a result, such 

 simple, satisfactory, and inexpensive methods of maturing dates 

 have been worked out that the commercial grower will do well 

 to rely on them. The exact process differs with the variety 

 and with the conditions under which the dates have to ripen ; 

 for the precise technique advisable in his case the grower must 

 either refer to those who have had the experience he needs, 

 or experiment on a few dates for himself, after he has grasped 

 the general principles. 



As W. T. Swingle points out, a date is botanically mature, 

 or "tree ripe" as horticulturists say, as soon as it reaches 

 full size and the seed is fully developed. At this stage, however, 

 the date is still astringent and not eatable. Following this 

 comes a process that may be called "ripening for eating," 

 consisting of complex chemical transformations by which the 

 sugars are altered and the tannin deposited in insoluble form 

 in " giant cells." This final ripening is brought about by the 

 combination of heat and a certain degree of humidity. 



The principle underlying modern methods of artificial ripening 

 is, therefore, to expose the dates to a constant high temperature, 

 while holding them in the humid atmosphere which is created 

 by the moisture they naturally give off as they dry and wrinkle. 



For this purpose the dates are picked when they first begin 

 to soften. Most varieties at this stage show translucent spots 

 while the remainder of the berry is still hard and remains bright 

 red or yellow in color. Dates taken from the tree in this condi- 

 tion will ripen successfully in three or four days if they are 

 packed loosely, stems and all, into a tightly closed box and left 

 at ordinary room temperature, the room being closed at night 

 to keep out cold air. Commercial growers provide a special 



