What if Tin Can and Aluminum Can Have No Lacquer Coatings?

Every inner of tin can and aluminum can is coated with protective lacquer. It protects the metal from corrosion and eventual destruction. Protects the food contents – contact of acid foods with metal causes the metal corrosion. Some metals are being absorbed into food causing off-taste, disagreeable odor and or change in color. And ultimately, protects the consumer from consuming potentially harmful food stuffs.
What if cans are not lacquered? How does it looks like when filled with organic acid?
I gathered two can representatives. One aluminum can and one tin can. I removed the top of aluminum can by cutting it with a sharp knife. Tin can cover was opened using a regular can opener. Lacquer coatings were removed by rubbing it vigorously it with industrial type sand paper. Rinse with tap water then filled with vinegar, about 1/4 of the container capacity.
tin can before vinegarI chose vinegar as representative of acidic foods. Results maybe slightly different with other food acids. I am going to do more test later.
After about three hours, a distinct brown to dark brown discoloration was evident around vinegar surface and the metal surface below the line got darker. Vinegar odor became slightly disagreeable.
tin can after vinegarAluminum can exhibited change only after three days. Vinegar to acid reaction seemed too fast. It might be as fast but with no visible signs. The part around vinegar surface showed numerous block dots. Aluminum soaked in acid got a cleaner look.
aluminum can after vinegarChanges above might actually happen to foods if the lacquer is defective, lacquer which contains pinholes. Gonna do a verification test with pinholes.
update as of May 15 2012 for tin can … After several days, the corrosion around the vinegar surface was more pronounced.  The space above also showed signs of rusting.  The cloudy vinegar became clear and few rainbow flakes were visible on surface.
tin can rusting

Marvin is the lead chocolate maker of Ben and Lyn Chocolate Inc. Has strong background in food research and development. Occasionally conducts training and lectures. Lecturer of Cocoa Foundation of the Philippines. Do coaching and consultancy services on his free time.

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