If you don't have a thermometer (candy or infrared), you can test to see if the fudge is ready using the iced water hack. After the fudge has boiled properly for about 10 minutes, you test it by dropping a small amount of the mixture into the glass/bowl of cold water. You’ll know that the fudge is perfect when this mixture sets and forms a ball that you can squeeze between your fingers without it sticking to them.