Black Spots on Your Canning Lids? Pinholing Explained

Uh-oh …

You opened your canning jar, and there are black spots on the underside of the lid.

What is it? More importantly, is your canned food still safe to eat?

It might be a normal case of “pinholing.”

What Is Pinholing?

Pinholing occurs when certain acidic foods or meats react with the metal on a canning lid.

This causes the metal to corrode, producing black material as a byproduct.

You might notice black spots—or what looks like black soot—on the underside of the lid when you open a canning jar.

Common culprits for pinholing include tomatoes, meats, and rhubarb, as they are acidic and can react with metal. When you clean the lid after discovering pinholing, you will be left with spots of corrosion.

To ensure the safety of canned food, always familiarize yourself with the signs that your canned food has gone bad.

If you find pinholing but no other signs of spoilage, your food is likely safe to eat.

Pinholing vs. Mold: Signs to Know

When you open a can and see black spots on the lid, it’s crucial to determine if it’s mold or pinholing.

While mold indicates spoilage and potential health risks, pinholing has no effect on the food’s safety.

To distinguish between the two, follow these steps:

1. Examine the black spots: Mold usually appears fuzzy, while pinholing looks like flat black spots.
2. Rub your finger over the spots: If they don’t move at all OR they smear like black soot, it’s pinholing.

If it’s fuzzy, different colors, or wipes off easily with no left-behind residue, it’s mold. If it smears black, soot-like stuff, it’s pinholing.

Also, pinholing leaves behind spots of corrosion in the metal. Once you wash the lid, and there’s little chips or holes in the metal coating of the lid, that verifies that it’s pinholing.

Hope that helps!