I use two torches facing each other and a deep socket of the appropriate size on a cordless drill. I just hold them in long enough for them to change colour, not even to red. I dump them out on a folded up wrung out wet bath towel, it sucks the heat out of the brass with out the worry of getting water inside the case.
It doesn't take a lot of heat to anneal brass you can do it with a candle even, rotating the neck in a flame until you feel heat in your finger from the head of the brass where you are holding it. Or you can dip it in hot casting lead(too dangerous for me)
The very BEST way is with an annealing machine as everything is exactly the same for each case, but they are expensive and unless you are doing large batches not a worthwhile investment.