i see a bunch of tiny pinholes or dark spots on the inside bottom of my aluminum pressure canner, is it still safe to use or is it corroded?

Diagnosis

The tiny pinholes or dark, grayish-black spots you are seeing on the bottom of your Presto 01755 aluminum canner are the result of "pitting corrosion." This occurs because aluminum is a highly reactive metal. When acidic foods (like tomatoes, fruits, or vinegars) or high-salt brines come into direct contact with the aluminum surface during the heating process, they strip away the protective aluminum oxide layer. This creates localized chemical reactions that eat tiny, microscopic craters into the metal. These spots are not "holes" in the sense that they go through the metal; they are surface-level depressions. You can confirm this by taking a cotton swab dipped in water and rubbing the spot. If the spot doesn't bleed a dark liquid and doesn't feel like a deep puncture that you can poke a needle through, it is surface pitting. If the spots are merely discolorations or shallow pits, the structural integrity of the 16-quart vessel remains intact, and the unit is safe for continued pressure canning. However, if you see actual perforations where water leaks into the outer jacket, the unit must be decommissioned immediately.

How to Fix It

Since pitting is a chemical change in the metal, you cannot "buff" it out without removing a significant amount of material, which is not recommended. Instead, focus on neutralizing the surface and preventing further degradation.

1. Empty the canner and allow it to cool completely to room temperature.
2. Wash the interior with a mild dish soap and a soft nylon sponge. Avoid using steel wool or scouring pads, as these create micro-scratches that accelerate future pitting.
3. To remove dark oxidation stains, create a paste of baking soda and a small amount of water. Apply the paste specifically to the dark spots and let it sit for 15 minutes.
4. Gently scrub the paste with a soft cloth in a circular motion, then rinse thoroughly with warm water.
5. Dry the interior completely using a lint-free microfiber towel. Any residual moisture left on the bottom can contribute to further oxidation during storage.
6. To create a temporary protective barrier, you can "season" the bottom by rubbing a very thin layer of neutral vegetable oil onto the base and heating it on low for 5 minutes before adding water for your next batch.

If That Didn't Work

If the spots continue to grow or the discoloration is stubborn, try these advanced recovery methods:

• White Vinegar Soak: Fill the bottom of the canner with a mixture of one part white distilled vinegar and three parts water. Simmer this mixture for 10 minutes. The mild acidity of the vinegar helps break down the surface oxidation without eating into the healthy metal. Rinse thoroughly with water afterward.
• Citric Acid Treatment: For heavy gray scaling, add two tablespoons of food-grade citric acid to a gallon of water and simmer for 15 minutes. This is more effective than vinegar for removing mineral buildup that often hides under the pitting.
• Commercial Aluminum Cleaner: Use a specialized aluminum polish or cleaner that does not contain bleach. Apply with a soft cloth, wipe away the residue, and wash the unit twice with soap to ensure no chemical residue remains before canning food.
• Replacement of Gasket: If you have been scrubbing the interior aggressively, check your rubber gasket for wear. Pitting often coincides with old age; if the metal is pitting, the gasket may be brittle. Replace it with a genuine Presto replacement gasket to ensure a tight seal.

Heads Up

• Avoid Acidic Direct Contact: Never place high-acid foods directly on the bottom of the aluminum pot. Always use the provided canning racks to keep jars elevated and prevent the food from reacting with the metal.
• No Bleach: Never use chlorine bleach on your Presto 01755. Bleach is extremely corrosive to aluminum and will cause rapid, deep pitting that can compromise the safety of the pressure vessel.
• Dry Storage: Always store your canner with the lid inverted (upside down) on top of the pot. This prevents moisture from being trapped inside, which reduces the formation of oxidation spots during the off-season.
• Inspect Every Use: Before every canning session, visually inspect the bottom for "bulging" or actual holes. If the metal begins to warp or thin significantly, replace the unit immediately to avoid a catastrophic pressure failure.