1. Soak in water overnight after cleaning.
2. Drain away all water in the morning and tie in a piece of muslin.
3. Hang for 8 hours.
4. Wash and make ready for use.

For usal :

1. Cook beans in water or pressure steam till just soft but whole.
2. Drain and reserve.
3. Heat oil and deep fry slices of potatoes.
4. Put on absorbent paper. Sprinkle with salt. Reserve all oil except 3 tbsp.
5. Add cummin seeds and curry leaves. Then add onions and fry till golden
6. Add beans and all powdered spices, salt and sugar. Mix well.
7. Put in a serving dish and cover with slices of fried potatoes.
8. Garnish with coconut and coriander leaves.
9. Serve hot with rice.