- Foil and stainless steel can trigger a galvanic reaction when cooking moist, salty foods.
- This reaction may cause discoloration and metallic residue on your dish.
- Acidic or salty foods increase the risk of aluminum transfer during cooking.
Picture it: It’s a cozy night at home, and you layer your favorite lasagna recipe into your trusty stainless steel baking dish, cover it tightly with foil and look forward to enjoying a delicious dinner. That might sound like a solid plan, but science warns otherwise.
“When aluminum foil is in contact with metallic cookware such as steel, iron or copper in the presence of moist food, you can unintentionally create a galvanic cell. This is the same chemistry behind the production of electrical energy in alkaline batteries and in the battery that makes your car work,” explains Humberto Maldonado, chemist and food safety expert at Organically Grown Company. In fact, he says that pairing those materials is the perfect recipe for galvanic corrosion—not a tasty lasagna.
When peeking through the glass window on your oven door, you might not even notice some of the telltale signs that this is occuring: little holes, black spots and a chalky substance forming on the surface of the foil. So, when you go to uncover the pan, you could be shocked to see that the top layer of your lasagna has become a silver or black color and may even have a bluish liquid sitting on top.
It won’t be an appetizing sight, but if you’re particularly hungry, you might still find yourself wondering if you can safely have a few bites. The answer is maybe so—but playing it safe and throwing the pasta away is a much safer bet.
“As unpleasant as it would be, in most real-life situations, aluminum transfer would be very low (in the microgram to low milligram range), well below toxic levels for healthy adults,” says Maldonado. “That is why the U.S. Food and Drug Administration considers aluminum contact materials generally safe for normal use.”
However, he notes that there may be an increased concern for individuals who are at higher risk for health problems, like infants and dialysis patients, and that there are certain situations and foods that can significantly increase aluminum uptake as a result of galvanic corrosion.
This includes highly acidic foods—such as tomatoes, pineapple, citrus, vinegar and wine-based sauces—foods with a high salt content and dishes with long contact times. Lasagna is typically a tomato-based dish with a good bit of salt, and it often cooks for quite a while in your pan. That means it’s especially likely to take in a bit more aluminum and not a great candidate for that night’s supper.
If you distinctly remember lining or covering a stainless steel dish with foil when cooking a particular meal and not experiencing these results, it’s probably because one of the elements necessary to create the chemical reaction wasn’t present: Two electrodes with different electrochemical potentials (stainless steel and foil, in this case), electrical contact between the two and an electrolyte to allow ion movement.
“Most foods contain water, dissolved salts and organic acids, which provide the mobile ions required for current to flow through the electrolyte,” says Maldonado.
To err on the side of caution, it’s a good idea to avoid bringing these elements together when cooking and storing food. The expert says to consider using food wrap alternatives, like parchment paper and food-grade plastic liners, when cooking on stainless steel cookware, but that aluminum foil can be safely used with non-metallic materials, including tempered glass and ceramic.
Now that you know some of the dos and don’ts of kitchen chemistry, you can get back to cooking your favorite meals without experiencing disappointing—or more chemistry lab-appropriate—results.
