how do you get the black stuff off the bottom of the presto canner pot? i've scrubbed and it's still stained

Diagnosis

The dark discoloration on the bottom of your Presto 01781 is typically a combination of carbonized food residue, mineral deposits from hard water, and aluminum oxidation. Because this model is constructed from heavy-duty aluminum, it reacts chemically with the high heat of a stove burner. When water evaporates or spills over the side of the pot, it leaves behind concentrated minerals that "bake" into the metal surface, creating a stubborn, blackened crust or a deep grey stain. This is often exacerbated if you use a gas range with a high BTU output or an electric coil that creates "hot spots." The black residue is essentially a layer of carbonized organic matter bonded to the oxidized aluminum. If you have already tried scrubbing with a standard sponge and dish soap without success, it is because the bond is chemical, not just mechanical; simple friction cannot break the molecular bond between the carbon and the aluminum oxide layer.

How to Fix It

To remove these stains without gouging the aluminum—which can create pits that lead to further staining—follow this chemical-lift process:

1. The Alkaline Paste: Mix 1/2 cup of baking soda with approximately 2 tablespoons of water to create a thick, toothpaste-like consistency. Apply this paste liberally to the blackened areas of the pot's exterior bottom.
2. The Activation Soak: Pour 2 cups of distilled white vinegar directly over the baking soda paste. It will fizz violently; this chemical reaction helps lift the carbonized particles away from the metal pores.
3. The Heat Cycle: Place the pot (without the lid) on the stove and bring a small amount of water to a simmer inside the pot. The heat from the bottom of the pot will activate the cleaning paste from the inside out, loosening the bond of the black residue.
4. The Gentle Scrub: While the pot is warm, use a nylon scrubbing brush or a non-scratch scouring pad (blue or green, but avoid steel wool). Scrub in circular motions, focusing on the edges of the burner rings.
5. The Final Rinse: Rinse thoroughly with warm water and dry immediately with a microfiber cloth to prevent new water spots from forming.

If That Didn't Work

• Cream of Tartar Acid Bath: For deep-set oxidation, mix 2 tablespoons of cream of tartar with a small amount of water to create a paste. Rub this into the black stains and let it sit for 30 minutes. The mild acidity of the cream of tartar reacts specifically with aluminum oxide to dissolve the grey-black tint.
• Bar Keepers Friend (Powder): Use the powder version of Bar Keepers Friend (which contains oxalic acid). Dampen the bottom of the pot, sprinkle the powder, and rub with a damp sponge. Do not leave this on for more than 5 minutes, as the acid can etch the aluminum if left too long.
• Boiling Vinegar Solution: Fill the pot halfway with a mixture of 1 part vinegar to 3 parts water. Bring it to a boil for 15 minutes. While the metal is heated and expanded, the acidity penetrates the pores of the aluminum, making it much easier to scrub the exterior stains away.
• Mechanical Plastic Scraping: If the "black stuff" is a thick, physical crust (carbon buildup), use a heavy-duty plastic putty knife or a nylon scraper to gently flake off the larger chunks before applying chemical cleaners.

Heads Up

• Avoid Steel Wool: Never use steel wool or metal scrapers on the Presto 01781. Aluminum is a soft metal; scratching the surface creates microscopic grooves where carbon and minerals will trap more easily, making future stains permanent.
• No Dishwashers: Never put the aluminum pot in the dishwasher. The harsh detergents used in dishwashers cause a chemical reaction that turns the aluminum a dull, dark grey/black color across the entire surface.
• Flame Management: To prevent future buildup, ensure your gas burner flame does not extend beyond the bottom edge of the pot. "Lapping" flames cause the sides of the pot to overheat and carbonize.
• Dry Storage: Always dry the exterior of the pot completely after washing. Storing the canner while the bottom is damp can lead to "pitting," which appears as small black dots that cannot be scrubbed off.