Yeast is good as it will be more immediately available for food as it will ferment faster than a rice grain and is already broken down. Our own Springtail Culture Food is composed of immediately available Vitamins serving as the best of Nutrients for your Springtails and is already broken down for Quick Assimilation. Grains like rice often contain eggs from several varieties of pests like gnats or moth. It is good to use these procedures you are doing in order to determine what will cause your colonies to thrive.