Term for grape must obtained from grapes by various mechanical methods (not to be confused with grape juice produced by further treatment). Strictly speaking, however, a distinction must be made between the must obtained by automatic draining free-run must and the must obtained by subsequent pressing. The must composition or its ingredients are of great importance for the quality of the later wine. Because of the sugar and other nutrients it contains, must is a very good breeding ground for yeasts and bacteria. Without appropriate measures such as pasteurisation or filtration, fermentation starts very quickly. The must is strongly enriched with carbon dioxide and therefore foams with corresponding noise. The ingredients also determine the necessary steps of must treatment. The unit of measurement to represent the relative density is called must weight (colloquially the sugar content, although other substances are also contained).