First, cut a piece of old ginger into small pieces and grind the ginger to fine. Then, squeeze the juice out by pressing the ginger through a sieve. Put the juice into a bowl. Next, bring the milk to a boil and dissolve sugar in milk. Take off heat and allow it to cool a little. If you have a kitchen thermometer, place your kitchen thermometer into the milk. The optimum curdling temperature is 70 °C (158 °F). In the mean time, stir the ginger juice thoroughly. When milk temperature decreases to around 75-70°C, pour the milk quickly into the middle of the ginger juice. Wait for two to three minutes. The milk will then be curdled, and may be eaten with a spoon.
Ginger contains the proteasezingipain. When milk is added to ginger juice, this protease catalyses denaturation of the protein in the milk, changing it from a water-soluble form to a water-insoluble form, and leads to the formation of milk curd.