Steps
1. Peel and grate the potatoes.
2. Wash and squeeze the pulp to remove free starch.
3. Squeeze lemons or limes and strain the juice.
4. Bring cloves and mace (or nutmeg) to the boil in a little water and strain off the extract.
5. Pack the potato pulp into a large stone jar.
6. Add sugar, lemon or lime juice and spice extract.
7. Add 4 1/2 l of cold water and stir until the sugar is completely dissolved.
8. Whisk in the beaten egg white, cover and allow to stand for 8 days.
9. Strain before drinking, if necessary.

Source
Food and Agriculture Organization of the United Nations (1990), Roots, tubers, plantains and bananas in human nutrition, ISBN 92-5-102862, Rome