A ripe melon should give slightly when pressed gently at one end. For rockmelon, press at the stalk end. For honeydew, press at the end opposite the stalk. You should also sniff the melon: a ripe one has a strong
The most probable explanation for pallid rubbery mince is that you are cooking the meat for too long at a temperature that is too high. For better results, the mince should be started over a medium-high heat in a large