The many alternate uses for Coca-Cola -- are they worth the price of a 2-liter bottle?
Some seem highly improbable (defrosting a frozen windshield by pouring a Coke on it? Drinking heated, flat Coke for decongestion? Adding it to your laundry to combat the smell of fish?) Others seem at least vaguely possible. How many of these are legit, and why would "The Real Thing" work for these tasks?
If it does do the job, you can credit one of three working ingredients in a bottle of Coke: phosphoric acid, sugar, or carbon dioxide. The acid is the same as the active ingredient in naval jelly, which is used to remove rust, but the soda has it in much lower concentration. Coke has a PH around 2.5, making it more acidic than apple juice but less than lemon juice.
The sugar is, of course, a nutrient, a highly-concentrated one, and if a biological entity (like you, for instance) can absorb it, it can be converted to energy. Bacteria that make mulch from yard waste might work faster after munching on some Coke. The CO2 is the bubbly part, and if you have an upset tummy, the fizz could help you burp, giving temporary relief.
We tried a few of these alternative uses just to see how useful Coke could be around the house.
Brownies: We found a recipe on Coca-Cola's site that showed us how to make low-fat brownies by mixing a couple of cups of Coke with a chocolate cake mix in place of the oil and eggs. We did, and yes, the brownies came out OK. However, the lack of grease robbed them of much of their chewiness. Using Coke did drop the overall calorie count of the brownie from 260 calories to 177, a significant difference.
However, I believe that any sugar soda could perform the same function, although the flavor of the brownie will be altered by the type of soda you use.
Pennies: We soaked five tarnished pennies in Coke for a day, and the acid in the drink actually did leave them looking much brighter. However, keep in mind that bathing coins in acid could very well kill off their value as a collectible. If you have a valuable penny, take it to a coin shop and ask their advice before doing any cleaning.
Rust: I was able to harvest 2.5 ounces of rust from my '95 Voyager. After soaking it in Coke for a day, over half an ounce of rust had been dissolved away, which surprised me. However, I have no idea how you could keep a rusty side panel immersed in Coke for a day, and even if you could, there are more concentrated de-rusters on the market that could do a better job.
Car battery terminals: Fortunately, I just happened to have a car battery terminal that was covered in acid crystal fuzz. I dumped some Coke on it and it dissolved the crystals completely. The only downside? Sticky sugar residue which I had to rinse off with a hose.
However, I wouldn't recommend this process; it could make things worse if the sugar syrup insinuates itself into the cable connection. Pulling off the connectors and giving this a thorough cleaning with a wire brush and perhaps some baking soda is a better solution.
Windshield: One of Michael's 51 uses is "Shake up a can and pour it over your windshield to remove bugs and other crud." This didn't work for me any better than the blue water that you find at gas stations. Much better is a bit of ammonia in water.
Having rubbed sugar all over my windshield, I'm curious to see how many flies chase me the next time I go out for a drive.
My conclusion? Yes, Coca-Cola might have attributes that allow it to be used for non-food purposes, but for almost all of those instances there are better alternatives, ones that are cheaper and/or work better. The big three household cleaners, vinegar, ammonia and bleach, are inexpensive and work very well. There are over-the-counter drugs to help you belch and oils to help you tan. As a lawn and flower spray, Coke is a very expensive solution. As a cooking ingredient, making your own sugar water is a cheaper way to go.
And what about the original use, as a beverage? Be aware of the sugar content; a one-liter bottle of Coke has almost half a pound of sugar in it.