Why are most copper cooking utensils lined with tin?
It’s widely believed that copper interacts with food to produce a toxic effect, and must be lined with another material to make it safe for use. Acidic foods can interact with the copper itself and leach minute amounts of it from the vessel. Although copper is a trace element that’s necessary to life and excess copper is voided by the body, significant amounts may produce an upset stomach. Therefore, If the tin linings of your copper pots are worn, you can use them — provided they’re free of any copper oxides and you’re not cooking highly acidic foods in them, but it is not recommended. The exterior of the copper pot is a less vital concern, but few who make the investment of copper are content to let their pots tarnish. Most professional cooks maintain the amber glow with liberal amounts of vinegar and coarse salt, which clean the copper gently. If the copper is heavily oxidized or you desire a brighter sheen, use a commercial cleanser. And in an emergency, you can use an imperfectly
