Peanut brittle without a thermometer

Yes, you really do need to start with raw peanuts. If you use already roasted or cooked peanuts they will be burned and nasty by the time the brittle portion is done. The raw peanuts will also have a color change and give you a roasted smell, which allows you to judge when cooking has finished. I'll be honest with you, this is one candy which definitely is easier and more dependably done with a thermometer. If you get one, then you can opt to use already roasted nuts and add them in at the last moment. Lacking one though, you need to use raw.