Mellowness is a state of being soft, ripe and tender. However, when we talk about antonyms for the word 'mellownesses,' we are actually looking for words that represent the opposite of these qualities. So, antonyms for mellownesses can include harshness, bitterness, roughness, sourness, and abrasiveness. These words signal a state of being that is opposite to mellowness in terms of texture, personality or flavor. While mellowness is typically characterized by a pleasing smoothness and a serene disposition, its antonyms indicate the presence of an unsettling roughness or uncomfortable sharpness that can be hard to bear.