Food works, but it's not ideal. The 'best' source of ammonia is normal, unscented household ammonia. it needs to be unscented though.
Basically you want to add enough ammonia every day to keep 4-5ppm of ammonia in the tank. After a week or two it'll drop and you'll see nitrItes. At this point you only need to maintain about 3ppm of ammonia in the tank every day.
If you can't get ahold of unscented ammonia, you can use a raw shrimp, like at the grocery store. Doing it this way, you don't have to do anything but test the water every couple of days..the shrimp will decay and continuously produce sufficient amounts of ammonia. However, you have a shrimp rotting in the tank, so this method can be a little smelly. I've not done a cycle this way, so I can't tell you exactly how strong the odor will be.
