A sterile-filtered 10% raffinose solution is commonly used as a carbohydrate additive when preparing defined or selective culture media. Because raffinose is a non-glucose carbon source, it is particularly useful in yeast genetics applications where repression of the GAL promoter must be avoided, such as experiments involving Saccharomyces cerevisiae GAL-regulated expression systems. The solution can be incorporated into media under aseptic conditions after sterilization, either by adding it directly to liquid cultures or to molten media that has been allowed to cool. This flexibility makes it suitable for preparing minimal, selective, or differential media formulations.