The fading of food during elutriation may not necessarily mean that it is dyed, but it may also be a normal phenomenon. Before finding out whether the discoloration of black sesame seeds is normal, let's first understand a water-soluble natural pigment-anthocyanin, which is the main color source of purple-black foods such as black rice, purple rice, black peanuts, black corn, black soybeans, mulberries, purple potatoes and purple cabbage. Anthocyanins are usually stored in vacuoles of plant cells and will dissolve into water when the cells are damaged. Therefore, it is normal that the water soaked in black sesame, purple rice and black peanuts will turn purple or light black.

first, from the appearance, the seeds of natural foods such as black rice, black sesame seeds and black peanuts should have a shiny surface, and the dyed black surface has no natural luster.

Second, peel off the skin to see the color. Black grain foods, such as black soybeans, black sesame seeds and black peanuts, should be light-colored inside. If they are peeled and found to have color on the inside, it can be inferred that they are dyed.

thirdly, the normal black sesame and black peanut will not change color immediately after being soaked in cold water, but will ooze color slowly. This color is not pure black and transparent, and the dyed black sesame and black peanut will fade quickly, and the aqueous solution is pure black and opaque.

Fourth, add vinegar or alkali to the water. The anthocyanin pigments contained in purple-black food have a special property: they turn red in acid and blue in alkali.