Is It Bad to Drink Expired Soda? The Facts

Drinking soda past its printed date is almost never dangerous, but it is rarely enjoyable. The date stamped on a can or bottle of soda is a quality indicator, not a safety deadline, and the beverage inside does not suddenly become toxic the day after that date passes. What does happen is a slow decline in flavor, fizz, and chemical stability that makes the drink taste increasingly off. The more interesting question is what actually changes inside the container over weeks and months, and whether any of those changes could genuinely affect your health.

What the Date on Your Soda Actually Means

Unlike raw meat or dairy, soda does not carry a federally mandated expiration date in the United States. The “best by,” “best before,” or “sell by” dates printed on soft drinks are set by the manufacturer and refer to when the product will taste closest to what they intended. After that date, the company no longer guarantees the flavor or carbonation level, but they are not claiming the product is unsafe. In practical terms, most sodas are stamped with dates ranging from three to nine months after bottling, depending on the brand and packaging type.

This distinction matters because a lot of perfectly drinkable soda gets thrown away by people who treat the date as a hard cutoff. The acidity of most sodas, typically falling between a pH of 2.5 and 3.5, creates an environment that is extremely hostile to the bacteria responsible for foodborne illness. Carbonation adds another layer of preservation. Together, these properties mean that an unopened soda stored at room temperature will remain microbiologically safe for a long time past its printed date. The question is not really safety; it is whether you will want to drink it.

How Flavor Falls Apart Over Time

The first thing you will notice in an expired soda is that it tastes flat. Carbon dioxide slowly escapes through the container walls or cap seal, and once enough is gone, you lose both the sharp bite of carbonation and the way it enhances your perception of sweetness and acidity. A flat cola does not just lack fizz; it tastes noticeably sweeter and more syrupy because CO₂ was doing real work in balancing the flavor profile.

Citrus-flavored sodas degrade faster than darker colas because their flavor compounds are chemically fragile. Lemon oil, for instance, is packed with terpenes that oxidize readily. As those compounds break down during storage, they produce off-flavor substances that give the drink a stale, sometimes vaguely turpentine-like taste.¹ Cola-type sodas, which rely more on caramel color and spice extracts, tend to hold their flavor longer, though they are not immune to staleness.

Sugar itself also changes over extended storage. In acidic solutions, sucrose gradually breaks down into glucose and fructose, which are sweeter individually but alter the overall flavor character. Over very long periods, those breakdown products can react with trace amino acids in the beverage to produce darkened color and off-tastes through a process called the Maillard reaction.² In a practical sense, this means a soda that has sat on a shelf for a year or two might look slightly darker and taste different from a fresh one, even if the seal is intact.

Cans and Plastic Bottles Age Differently

The packaging your soda comes in plays a surprisingly large role in how it holds up over time, and the concerns are different for aluminum cans than for plastic bottles.

Aluminum cans are lined with a thin polymer coating to prevent the acidic drink from directly contacting the metal. Over time, that lining can degrade, especially if the beverage inside becomes slightly more acidic as its chemistry shifts. Research on canned soft drinks has found a clear and significant rise in aluminum content as storage time increases, pointing to gradual dissolution of aluminum from the packaging into the drink.³ The combination of increasing acidity and long storage accelerates this corrosion, leading to higher aluminum levels in older samples. Whether the amounts involved are enough to matter for health is debated. Occasional exposure to slightly elevated aluminum from a single old can is not going to cause problems, but it is one more reason not to make a habit of drinking soda that has been sitting in a warehouse for years.

Plastic bottles, overwhelmingly made from PET (polyethylene terephthalate), present a different set of issues. PET is not perfectly inert. Over time, small amounts of antimony, a metal used as a catalyst during plastic manufacturing, can leach into the beverage. One study found that antimony levels in carbonated drinks stored in PET bottles increased over time, along with shifts in acidity and other chemical properties.⁴ The same research conducted a health risk assessment and found that the tolerable dose index and hazard index remained below one for both adults and children, meaning the levels detected were not expected to cause harm from typical consumption. That said, the researchers did note that prolonged consumption of carbonated drinks stored well past their expected shelf life could contribute to fatigue and headaches in the short term, and flagged children as a more vulnerable population.

Glass bottles, for their part, are chemically inert and do not leach anything into the drink. If you happen to find a sealed glass bottle of soda past its date, the only real concern is flavor degradation and carbonation loss, not chemical migration from the container.

The Preservative Problem at High Temperatures

Most commercial sodas contain sodium benzoate as a preservative, and many also contain citric acid or ascorbic acid (vitamin C). Under normal storage conditions, this combination is stable and safe. But when those beverages are exposed to elevated temperatures or ultraviolet light for extended periods, sodium benzoate and ascorbic acid can react to form benzene, a known carcinogen.

Research has shown that under intense UV exposure, benzene levels in model beverage solutions increased by as much as 53 percent in non-UV-stabilized bottles.⁵ Separately, studies on sodium benzoate stability found that at moderately elevated temperatures around 40°C (about 104°F), sodium benzoate concentrations generally increased across samples, but at 60°C (140°F), levels dropped to less than half or became undetectable, suggesting the preservative was degrading, potentially into benzene.⁶

To be clear, the benzene levels involved in these studies are extremely small. Nobody is getting acute benzene poisoning from an old soda left in a hot car. But the finding does reinforce an important practical point: how you store soda matters much more than the printed date. A soda kept in a cool, dark pantry for six months past its “best by” date is in far better shape chemically than one that spent a summer in a hot garage within its date window. If you have cases of soda that have been sitting in direct sunlight or a non-climate-controlled shed, the date on the can is the least of your concerns.

Storage Conditions Trump the Printed Date

Temperature is the single biggest factor determining how fast a soda degrades. Heat accelerates every process that makes soda worse: carbonation escapes faster, flavor compounds oxidize more quickly, sugar breaks down sooner, and chemical reactions between preservatives and acids speed up. A consistent room temperature of around 20-22°C (roughly 68-72°F) is ideal for long-term storage. Every degree above that shortens the window of acceptable quality.

Light is the other major enemy, especially for sodas in clear or green plastic bottles. UV exposure drives oxidation of flavor compounds and, as noted above, promotes benzene formation in beverages containing the right combination of preservatives and acids. Dark-colored or opaque containers offer meaningful protection. If you are stockpiling soda for some reason, keep it in a cool, dark place and it will remain drinkable for months past the date with only minor quality loss.

Refrigeration extends quality significantly. Cold temperatures slow chemical reactions and dramatically reduce the rate at which CO₂ permeates through plastic. A refrigerated PET bottle of soda will stay fizzy and flavorful far longer than one stored at room temperature. Research on functional beverages stored at 4°C after expiration found a chemically stable period that lasted several weeks before any measurable degradation began.⁷ While that study focused on functional drinks rather than standard soda, the principle holds across carbonated beverages: cold storage buys time.

Once You Open It, the Rules Change Completely

Everything discussed so far applies to unopened containers. The moment you crack the seal on a soda, you introduce an entirely different set of risks, and these are worth taking seriously even if the expiration date is still months away.

An opened soda left at room temperature becomes a potential growth medium for bacteria, molds, and yeasts. Research examining microbial contamination in beverages after opening found that drinking directly from the bottle was far worse than pouring into a glass. In tests where people drank directly from the bottle, microbial growth was detected in roughly half of the samples, with 225 bacterial strains, 27 mold strains, and 77 yeast strains isolated. Even in the more cautious pouring test, contamination was detected in about one in five samples.⁸ The organisms involved included foodborne pathogens, and room-temperature storage allowed them to multiply rapidly.

The acidity that protects sealed soda from microbial contamination is still present after opening, but it is no longer enough on its own once you have introduced bacteria from your mouth and hands. The carbonation that also helps suppress growth escapes rapidly once the bottle is open. If you open a soda, your best bet is to finish it within a few hours, or cap it tightly and refrigerate it. An opened soda left on a countertop overnight is a much more realistic food safety concern than a sealed can that is three months past its best-by date.

Diet Soda Ages Worse Than Regular

If you have ever tasted a diet soda that has been sitting around for a while, you may have noticed it tastes markedly worse than a similarly aged regular soda. This is not your imagination. The artificial sweetener aspartame, used in most diet colas, breaks down over time, especially in acidic solutions and at warm temperatures. As aspartame degrades, it loses its sweetness and produces breakdown products that can give the drink a bitter or off-putting taste. The rate of degradation increases significantly with heat, so a diet soda stored in a warm environment will lose its sweetness profile much faster than one kept cool.

This breakdown is a quality issue, not a safety one. The products of aspartame degradation, primarily phenylalanine and aspartic acid, are amino acids that your body encounters in food daily. They are not harmful at the levels you would get from a degraded diet soda, with the exception of people who have phenylketonuria (PKU), a metabolic condition that prevents proper processing of phenylalanine. For everyone else, the problem with old diet soda is purely that it tastes bad. Where a regular soda might be tolerable months past its date, a diet soda stored in even mildly warm conditions may become essentially undrinkable well before the printed date.

Drinks Stored for Years, Not Months

Most discussions about expired soda focus on the window of a few weeks to a few months past the date. But what about soda that has been sitting in a basement or collector’s shelf for years? This is where the aluminum leaching concern becomes more relevant. The research on canned beverages found that the combination of long storage times and the slight increase in acidity that occurs during aging led to a significant accumulation of aluminum in older samples.³ Collectors who open and taste vintage sodas from the 1990s or earlier are drinking something with a measurably different chemical composition from a fresh can.

At the multi-year timescale, you also lose essentially all carbonation, regardless of packaging type. The flavor will have shifted noticeably. Citrus sodas will likely taste oxidized and stale. Colas may taste flatter and darker. The sugar chemistry has had time to progress through stages of inversion and browning. None of this makes the drink acutely dangerous in a single serving, but it is far from the product the manufacturer intended, and calling it “soda” at that point is generous.

What to Actually Look For Before Drinking Old Soda

If you find a forgotten can or bottle of soda and you are wondering whether to drink it, the printed date is the least useful piece of information. Here is what actually matters:

Container integrity: Is the can dented, swollen, or leaking? Is the bottle cap compromised or the bottle deformed? Any damage to the seal means the contents are unpredictable. Toss it.
Carbonation: When you open it, does it hiss? If there is no pressure release at all, the seal likely failed at some point, or the CO₂ has fully permeated through the plastic. The drink is probably safe but will taste flat.
Storage history: Has this been in a temperature-controlled space, or in a shed, trunk, or attic? Heat exposure accelerates every form of degradation and is the single most important variable.
Appearance: Unusual cloudiness, floating particles, or dramatic color changes in what should be a clear beverage suggest chemical or microbial changes worth avoiding.
Smell and taste: If it smells off or the first sip tastes wrong, trust your senses. You are not going to miss out on anything by pouring it out.

Why Soda Is Not Like Milk or Juice

People sometimes treat all beverage expiration dates the same way, but soda occupies a very different spot on the safety spectrum than dairy, juice, or even water. Milk supports bacterial growth readily because of its neutral pH and rich nutrient content. Fruit juice, while acidic, often contains enough nutrients and lower preservative levels to allow microbial growth after pasteurization effects wane. Water in plastic bottles faces the same chemical migration concerns as soda but without the antimicrobial benefit of acidity and carbonation.

Soda’s combination of high acidity, carbonation, chemical preservatives, and high sugar concentration makes it one of the most shelf-stable beverages you can buy. The trade-off is that it was never nutritionally valuable to begin with, so the loss in quality from aging does not represent a loss of health benefit the way deteriorating juice or milk might. You are not losing vitamins or beneficial bacteria. You are losing fizz and flavor in a product that was engineered for fizz and flavor. Once those are gone, the only remaining question is whether the chemical changes in the container are worth worrying about, and for a single serving found a few months past the date in reasonable storage conditions, the honest answer is no.