Drinking expired soda is unlikely to make you sick, but the quality drops noticeably over time, and in some cases the packaging itself becomes the bigger concern. Soda doesn’t spoil the way milk or meat does. Its high acidity and carbonation create an environment where dangerous bacteria simply can’t survive. What changes after the expiration date is taste, carbonation, and in certain cases, the chemical makeup of the drink and the materials it’s stored in.
What the Date on the Can Actually Means
Soda doesn’t have a true expiration date in the way perishable foods do. The date printed on the can or bottle is a “best by” date, which tells you when the manufacturer expects the flavor and fizz to start declining. It’s a quality marker, not a safety cutoff.
That said, the window for acceptable quality isn’t unlimited. The USDA recommends drinking unopened regular soda within nine months past its best-by date, and diet soda within just three months. The shorter window for diet drinks isn’t arbitrary. It reflects real chemical changes happening inside the container.
Why Diet Soda Degrades Faster
Regular soda is sweetened with sugar or corn syrup, both of which are chemically stable over long periods. Diet soda uses artificial sweeteners, and those break down. Aspartame, the most common one, gradually splits into its component parts: two amino acids (phenylalanine and aspartic acid) and a small amount of methanol. That methanol gets further converted in your body into formaldehyde and formic acid.
In a fresh can of diet soda, the amount of methanol produced during digestion is tiny and well within safe limits. But as aspartame degrades over months or years on a shelf, the chemistry of the drink shifts. The sweetness fades, an off-taste develops, and the breakdown products accumulate. This is why diet soda left in a hot garage for a year tastes noticeably wrong. Heat accelerates the process significantly.
For anyone with phenylketonuria (PKU), a genetic condition that prevents the body from processing phenylalanine, this degradation matters even more. But for most people, the primary consequence of drinking old diet soda is simply a flat, chemically off-tasting beverage.
Bacteria Aren’t the Problem
One reason people worry about expired drinks is the assumption that harmful bacteria might grow over time. In soda, that’s essentially a non-issue. Most soft drinks have a pH below 4.0, which is acidic enough to prevent the vast majority of disease-causing bacteria from surviving, let alone multiplying. Carbonation adds another layer of protection by creating a low-oxygen environment.
Yeasts are the one group of microorganisms that can tolerate both the acidity and carbonation of soda. They thrive in a pH range as low as 1.5 and can grow even under high carbonation. If a can or bottle has a compromised seal, yeast contamination is possible, and you’d notice it: the drink would taste fermented, smell off, or the container might bulge from gas buildup. Mold spores can survive in soda but need oxygen to grow, so they’re only a factor once you’ve opened the container and left it sitting.
In practical terms, an unopened soda that looks and smells normal is not harboring dangerous pathogens, regardless of the date on it.
The Can Itself Can Be a Problem
The more meaningful concern with very old soda isn’t what’s in the drink. It’s what the container is releasing into it. A study analyzing 104 carbonated beverages, including some stored five years past their shelf life, found that aluminum levels in canned drinks rise significantly over time. The acidic liquid slowly dissolves the inner lining of aluminum cans, and dissolved aluminum leaches into the beverage.
Glass bottles showed intermediate aluminum levels, and plastic (PET) bottles had the lowest. So the type of container matters if you’re dealing with soda that’s been sitting for years rather than months. A can from the back of a pantry that’s a few months past its date is one thing. A forgotten case of cans from several years ago is a different situation, and probably not worth drinking.
How to Tell If It’s Still Fine
Your senses are a reliable guide here. Open the can or bottle and check for three things:
- Carbonation. If it’s completely flat, the seal may have been compromised, or the CO2 has simply escaped over time. It won’t hurt you, but the drink has lost its defining characteristic.
- Smell. Any fermented, vinegary, or chemical odor means something has changed beyond simple aging. Pour it out.
- Taste. A small sip will tell you if the flavor has degraded to the point where it’s not worth finishing. Diet sodas in particular develop a distinctly unpleasant, almost metallic taste as their sweeteners break down.
If the container is bulging, leaking, or visibly corroded, skip the taste test entirely and throw it away.
Storage Conditions Matter More Than the Date
A soda stored in a cool, dark pantry ages very differently from one left in a hot car or a sunny garage. Heat accelerates every form of degradation: carbonation escapes faster, artificial sweeteners break down sooner, and can liners deteriorate more quickly. A can that’s one month past its date but spent the summer in a hot trunk may be in worse shape than a can that’s six months past its date but stayed in a climate-controlled kitchen.
If you’ve been storing soda at a stable room temperature, the USDA’s guidelines of nine months (regular) and three months (diet) past the printed date are reasonable benchmarks. Beyond that, quality declines enough that most people would choose to grab a fresh one instead.