Dr Keith Souter writes: I also like doing little experiments that you can perform at home. For example, you can actually use tea to check food for iron content. You may even find it fascinating enough to start your own chemical analysis of common foods. You need a few jars, depending on how many foods you plan to study, a food blender, or failing that a good fork to mash the food up, and some paper coffee filters. To start, brew a pot of strong tea (using five or six tea bags, more than you would normally use for drinking) and allow it to cool. It needs to be as strong as possible. Now prepare the food that you want to test. Simply pop a couple of spoons of it in the blender or macerate it with a fork. Add just enough water in order to make a puree. Once it is fluid enough, filter it through the coffee filter into a jar. Gradually add tea and gently stir. If there is iron in the food, you will start to see a black precipitate begin to form. That is, a black powder will start to appear. Allow it to settle for about five minutes then filter through a fresh coffee filter. You have actually extracted the iron from the food. Thus, you can compare amounts in different foods. What happens is that the tannins in the tea will chelate the iron in the food and it gets thrown down as a precipitate. Chelation is the name for a process by which certain ions and molecules bind metal ions. Iron is easily chelated by the tea tannins and this black precipitate is iron tannate. There is a serious point to this experiment. If you tend to be anaemic or if you are on iron tablets from the doctor, don’t have tea within half an hour of meals or of the tablets. This is especially the case with plant-based iron, so vegetarians and vegans should take note. Have it after a gap of half an hour and there is no problem. Also, if you take your tea with lemon, the vitamin C will help to absorb the iron.