The presence of lipids can be tested using the grease spot test and the Sudan Red test. The grease spot test involves placing a sample on an unglazed brown paper bag and looking for translucent spots that are left behind. The Sudan Red test involves using Sudan Red, a fat-soluble dye, that stains lipids red.
Lipids are molecules that contain mostly hydrocarbons, and they are one of the main building blocks of life. As a result, they can be extracted from both plants and animals. Some examples of lipids include fats, oils, certain vitamins and hormones. Lipids make up a huge component of the non-protein membranes of all cells.