lipids, a group of chemicals that includes oils, fats, and waxes. Lipids are distinctive in plants because, despite the plant’s watery environment, they are not soluble in water, which is also the basis of their important roles. They make up the membranes of plant cells which keep apart entirely different zones of metabolic activity, often with large differences in acidity on either side of the membrane. They make energy-rich reserves of food as in seeds, grapeseed oil being a good example. Also they coat the surface of the plant with a water-impermeable layer of waxy cutin which stops desiccation. A host of other compounds have lipid-like structures, including important plant pigments such as chlorophyll and carotenoids. The sediment in must contains a significant amount of lipids that play an important role in fermentation. If clarification of the must is too severe (so that the turbidity is less than 150 NTU), the risk of sluggish fermentation is higher than in more turbid juices with higher levels of solids.