Purple yam is not a perishable crop. Can still be marketed tomorrow if not sold today. Can still be sold the next week or the next month. However, it will dry up slowly and will loss its market value. The best way to make it last long is intentional drying.
1) Dip ube in slow boiling water for few minutes. This will prevent skin itching while peeling. Experiment result showed that ube skin contains most of the substance responsible for itching. Dipping in hot water is able to degrade the harmful substance.
2) Let cool. Slice as thin as possible, the thinner the better. Thinner slices will allow faster drying time. Using a fruit peeler will get the job done with ease.
3) Arrange slices in metal or aluminum tray. Make sure that every slices can get ample heat from the sun. Do not use plastic trays.
4) Dry under the sun for two days. Drying time may take longer depending on weather condition. Drying is done when the purple yam slices are crispy.
Notice the browning reaction on some of ube slices. It is natural because I never used any color stabilizer. Browning can be prevented by dipping the slices in solution of sodium erythorbate before drying.
5) Grind the dried slices using manual/electric grinder or blender. Then pack in a sealed container.
Our blender is not working. I used mortar and pestle to granulate the ube. I will redo the work once the blender is fixed.
update as of May 1, 2012. I passed it through manually operated steel mill. I got a more fine powder that I used for making ube haleya.