You can add 1 teaspoon of all-purpose flour to the yogurt. It will prevent it from curdling and will also make the curry thicker.If the guava has large seeds, then remove them.Choose firm and ripe guava to make this curry. If the guava is raw, it will taste bitter and if the guava is overripe, the curry will taste sweet and mushy. Pick up guavas that are free of blemishes and bruises. Some guavas have pink flesh, you can use them too.