Since it was first invented by John Pemberton in 1886, Coca-Cola has become one of the world's best selling soft drinks. Coke is sold in more than 200 countries around the world, and the name is often used as a generic term to describe all cola. You may not think of Coke as a product that's in danger of "going bad," but its quality will suffer under certain circumstances.
Best Before Date
Whether it's in a can, plastic bottle or glass bottle, all servings of Coke have a “Best Before Date” printed on them. This date lets retailers and customers know that the product is at its highest quality prior to that date, according to Coca-Cola. Unopened Coke products will retain their shelf life for six to nine months after the Best Before Date, in the pantry or the refrigerator.
What Bad Coke Tastes Like
Most soft drinks lose carbonation, or go "flat," after opening if not stored properly. If you leave opened Coke sitting overnight, or store it unopened for more than nine months past the Best Before Date, you'll be left with a flat product that isn't very appetizing. If your Coke does taste sour or "off," stop drinking it immediately. Diet Coke contains artificial sweeteners that are known to break down chemically over time, so it's especially important to avoid it if it tastes flat or spoiled.
Keeping It Fresh
If you're interested in keeping your Coke fresh longer than the date on the bottle or can, store it in a cool, dark place with a constant temperature, such as your pantry. Storing it in the refrigerator also works. Use the date on the bottle or can as a guide, and drink it within nine months of the date for best results.