In a pan combine together pineapple,turmeric powder,kashmiri chili powder ,salt and water.Cover and cook over medim flame until pineapple turns soft.Meanwhile,add all the ingredients listed under "For coconut paste' in a blender.Grind this to form a smooth paste ,adding sufficient quantity of water.
Once the pineapple turns soft,add the coconut paste .Cook for few minutes until the gravy turns thick.
Add the grapes and switch off the flame.Immediately add the yogurt,crushed mustard seeds ,sugar and more salt,if required.Stir continuously until combined to avoid curdling.
For Tempering,heat oil in pan and add mustard seeds,let it splutter.Add dry red chilies and curry leaves,saute for few seconds.
Immediately add this to the prepared curry .Cover and set aside for atleast 10 minutes.Uncover ,stir gently and serve with rice.