Is there a simple way to clean crusted, built-up coffee residue in a metal or enamelled pot (aside from steel wool)?
Coffee pot cleaners come in two "flavours": acidic and alkaline. The acidic ones, which include white vinegar, are great for removing the mineral deposits that build up inside coffee makers and clog the openings where water needs to drip out. The alkaline cleaners remove crusted coffee residue, such as what you're dealing with. But to answer your question, it's also important to realize that "metal or enamelled" covers a lot of territory. Stainless steel isn't the same as aluminium, and enamel is a finish, which means scrubbing with something highly abrasive like steel wool could wear through it.
Any alkaline solution will combat coffee crusts and coffee stains, said Isaac Cohen, vice president for marketing at Urnex Brands. Commercially formulated cleaners often also include ingredients to help with factors such as solubility and rinsing efficiency.
When coffee remains are thin and are more like a stain than a thick crust, baking soda can be a very effective cleaner, especially if you combine it with water, heat and time. Paul Genovese, a customer service representative for GSI Outdoors, which makes a vintage-looking blue enamelled coffee pot sold by retailers such as REI for camping, recommended filling a coffee-stained pot with water, heating it to boiling and scooping in a couple of tablespoons of baking soda. Simmer for a while, and the stains should come right out, without any need to scrub with an abrasive that might scratch the porcelain-enamel surface, he said.
On the pH scale for comparing acids and bases, baking soda has a pH of eight, making it one of the gentlest alkaline cleaners. If it isn't powerful enough for your pot, escalate to something with a pH around 11. Dishwasher detergent tends to be in this range, as are cleaners labelled specifically for removing coffee crust.
For cleaning large urns and coffee-making equipment, coffee shops often use a product such as Urnex Original Urn & Brewer Cleaner or Puro-branded cleaners, which are also made by Urnex. The urn and brewer cleaner has a pH of 11.2. For home use, Cohen recommends Urnex's Coffee Machine Cleaning Liquid ($7.99 – R131,30 for a 14-ounce bottle at urnex.com). It has a pH of 11.4. The instructions, written for automatic coffee makers, say to use 1 / 3 of the bottle (just under five ounces) to clean a full pot. For many brands of coffee makers, a full pot is 10 to 12 cups, so if your crusted pot is considerably bigger or smaller, you might need to adjust the dilution formula. "Let it sit for 15 to 30 minutes," Cohen said. "Then scrub it off. It will loosen [the crust] and take off discolouration from oils." If you clean regularly, the soak alone may be sufficient; you might not need to scrub, he said.
Coffee cleaners marketed to consumers also include products such as Squeak'n Clean Ultimate Coffee Pot Cleaner ($3.99 – R65,37 for a 12-ounce bottle on buycoffeehere.com).
Whatever brand you use, be aware that any cleaner with a pH around 11 is as caustic as household ammonia, so wear gloves. The safety instructions with Squeak'n Clean specify rubber, vinyl or neoprene.
The big caveat with alkaline cleaners is not to use them on aluminium. "The cleaners would remove the coffee crust but also some of the aluminium," Cohen said, leaving the metal pitted and dark, just as aluminium coffee scoops or whip attachments for mixers emerge from a dishwasher. However, Urnex's Coffee Machine Cleaning Liquid can be used on aluminium, Cohen said, because it contains a corrosion inhibitor, sodium silicate.
Urnex's basic cleaner for commercial coffee urns and brewers used to have only one listed ingredient: trisodium phosphate, or TSP. TSP is very effective, but the phosphate it contains triggers algae blooms if it winds up in streams, lakes or places such as Chesapeake Bay. The algae growth depletes oxygen in the water and causes fish to die, which is why TSP is now banned in household cleaners in many areas. TSP is still found in some cleaners marketed for commercial uses, when TSP substitutes aren't as effective. "If you make a carafe of coffee a day, your cleaning needs are very different from a business with an espresso machine" that might pump out 300 to 500 drinks a day, Cohen said.