The process of filling a vat with uncrushed grapes, where the grapes at the bottom of the vat are gradually crushed under pressure from the top grapes. Juice is released from the bottom grapes and begins to ferment. This fermentation releases carbon dioxide, which causes the uncrushed top grapes to ferment within their skins. This process is commonly used with young fruity wines with low tannins such as Beaujolais Nouveau.