When unbroken grapes are surrounded by CO₂, they begin to absorb the CO₂ and initiate a yeast-free and oxygen-free fermentation. The resulting fermentation process is the same as what happens with conventional maceration: the yeast converts sugars into alcohol, and the anthocyanins begin to diffuse into the centres of the grape, staining the resulting juice a pinkish-red colour. A major sensory change occurs at this stage because less tannins diffuse into the flesh than do cyanins, so the juice inside the unbroken grapes will be less tannic than it would be in a conventional maceration.