Wash the grapes, pat them dry and cut them into halves, lengthwise.
Add the sugar, salt and chilli powder to the yogurt and whisk with a fork till it is smooth. Fold the chopped grapes into the yogurt and chill till youu2019re ready to serve the Raita.
Just before serving, transfer the Raita into a serving bowl. Heat the oil in a small pan, and add the mustard seeds. When they splutter, add the lentils and turn the heat down to low. Stir this until the lentils turn a golden brown. Then add the fenugreek and cumin seeds, and the asafoetida. Stir once or twice and turn off the heat. Add the curry leaves and pour this into the yogurt.