Metabolites are intermediates in metabolic processes in nature and are usually small molecules. A primary metabolite is directly involved in normal growth, development, and reproduction, for example, fermentation products (ethanol, acetic acid, citric and lactic acid) and cell constituents (lipids, vitamins, and polysaccharides). A secondary metabolite is not directly involved in those processes and usually has a function but is not that important for the organism (e.g., antibiotics, pigments, and carotenoids).