An activator is a substrate you add to get the composting process going. In most of these activators the main source is a high level of nitrogen (protein), the nitrogen will help the microorganisms to start breaking down the material. 

 Because kitchen waste is a high source of nitrogen it's a super good activator, when your allowed to compost meat, fish, chicken etc it becomes even a better compost activator and this is why you never have to buy activator with a Joraform Compost tumbler. It's specifically made for kitchen waste including all sorts of meat with bones.