Drinking expired pop is almost certainly not going to make you sick. Carbonated soft drinks are highly acidic, heavily preserved, and inhospitable to most harmful bacteria. What you will notice is a flat, off-tasting beverage that has lost much of what made it enjoyable in the first place. The date stamped on your can or bottle is a “best by” quality marker, not a safety deadline.
Why Expired Pop Rarely Makes You Sick
The environment inside a sealed can or bottle of soda is hostile to dangerous microorganisms. The combination of high acidity (most sodas sit around pH 2.5 to 3.5), dissolved carbon dioxide, and chemical preservatives like sodium benzoate makes it extremely difficult for pathogens to survive. Common foodborne bacteria like E. coli and Salmonella can only last about 48 hours in cola, and they’d need to get inside the sealed container in the first place.
The main spoilage organisms that can tolerate those conditions are certain yeasts, particularly a species called Zygosaccharomyces bailii, which can handle both high carbonation and preservative concentrations. If these yeasts do get a foothold, you’ll know before you take a sip: fermentation produces gas pressure that causes cans to bulge and bottles to swell. In extreme cases, it can produce enough ethanol to technically push the drink past the legal limit for a nonalcoholic product. A bulging or leaking container is the one clear sign you should throw it away. A normal-looking, properly sealed container that’s a few months past its date is a different story entirely.
What Actually Changes Over Time
The real consequence of drinking old pop is that it tastes worse. Several things degrade simultaneously.
Carbonation slowly escapes through the container walls. In aluminum cans, this happens slowly, with only about 1% to 5% of the CO2 lost per year. A can at its expiration date still holds over 95% of its original fizz. Plastic bottles lose carbonation much faster, at rates of 15% to 50% per year, and that rate doubles for every 10°C (18°F) increase in storage temperature. A plastic bottle of pop that’s been sitting in a hot garage for a year past its date will be noticeably flat.
Flavor compounds break down too. Citrus-based flavors are especially vulnerable to oxidation, producing stale, off-putting tastes. Colors fade when exposed to light and oxygen. Storage above 20°C (68°F) accelerates all of these changes. A can stored in a cool, dark pantry will taste much closer to fresh than one that sat on a shelf near a window.
Diet Soda Expires Faster Than Regular
If your expired pop is a diet version, expect it to lose its taste sooner. The USDA recommends consuming unopened diet sodas within three months of their expiration date and regular sodas within nine months. The difference comes down to artificial sweeteners.
Aspartame, the most common sweetener in diet drinks, breaks down in acidic environments over time. It hydrolyzes into its component parts, including the amino acids phenylalanine and aspartic acid, plus a small amount of methanol. This is the same breakdown that happens in your digestive system when you drink fresh diet soda. The amounts involved are tiny and not a health concern. But as the aspartame degrades on the shelf, the drink loses its sweetness and can develop an unpleasant, slightly bitter or chemical taste. Regular soda uses sugar or corn syrup, which are far more chemically stable and hold up much longer.
Cans vs. Plastic Bottles
Your container makes a real difference in how well pop ages. Aluminum cans have a thin polymer lining that prevents the acidic drink from contacting the metal, and they form a much tighter seal against gas exchange. They lose carbonation 30% to 50% more slowly than plastic bottles and offer better protection against light and oxygen.
Plastic bottles are more porous. CO2 permeates through the PET plastic over time, and oxygen can slowly seep in, accelerating flavor breakdown. Plastic surfaces also have higher roughness and tend to harbor more microorganisms than glass or metal, though this matters more for opened containers. If you’re deciding whether to drink something old, a can that looks and sounds normal when opened is your safest bet for decent quality.
The one scenario where can integrity becomes a concern is extreme storage conditions over very long periods. Research on acidic beverages stored in aluminum cans has shown that liner blistering (where the protective coating breaks down) can occur after about 48 weeks, but this was observed in highly acidic specialty products, not standard sodas. For typical pop, the liner holds up well within any reasonable timeframe past expiration.
How to Read the Date on Your Pop
Most major soda brands use straightforward “Best By” or “Best If Used By” dates printed directly on the can or bottle. Dr Pepper, for example, prints both a manufacture date and a “BIUB” (Best If Used By) date in a simple month/day/year format. Coca-Cola and Pepsi products typically use similar readable dates on the bottom of cans or on bottle caps.
These are quality dates, not expiration dates in the way that dairy or meat products have them. The FDA does not require expiration dates on soft drinks. The manufacturer is telling you when the product will start tasting less than ideal, not when it becomes unsafe. A pop that’s a month or two past its printed date is virtually identical to a fresh one. Six months to a year past, you’re mostly dealing with less fizz and duller flavor. Years past, you’re in “why bother” territory for taste, but still unlikely to get sick from a properly sealed container.
Signs You Should Actually Throw It Out
- Bulging or swollen container: This indicates fermentation from yeast contamination. The pressure inside can be significant, reaching 2 to 7 bars of gas in lab conditions.
- Leaking or damaged seal: Any breach in the container means outside microorganisms and oxygen have gotten in.
- Visible sediment, haze, or ropiness: These are signs of bacterial or yeast growth, sometimes caused by lactic acid bacteria in drinks containing fruit juice.
- Foul or fermented smell on opening: Spoilage yeasts produce ethanol and other off-odors that are immediately noticeable.
If the container looks normal, opens with a satisfying hiss of carbonation, and smells fine, you’re looking at a quality issue rather than a safety one. It might taste a little flat or slightly off, but it won’t hurt you.