Your orange juice tastes carbonated because yeast or bacteria in the juice have started fermenting its natural sugars, producing carbon dioxide gas as a byproduct. This is the same basic process that makes beer and wine bubbly, and it can happen in any sugar-rich fruit juice given enough time and the right conditions. The fizz means your juice has begun to spoil.
What’s Happening Inside the Juice
Orange juice is packed with sugar, and that makes it an ideal food source for microorganisms. Yeasts are the most common culprits. Species like Saccharomyces cerevisiae (the same yeast used in brewing and baking), Candida parapsilosis, Torulaspora delbrueckii, and Zygosaccharomyces rouxii are all naturally found in citrus juices. When these organisms consume the sugars in your juice under low-oxygen conditions, they produce three main things: ethanol (alcohol), carbon dioxide, and glycerol.
The carbon dioxide is what creates the fizzy sensation on your tongue. It dissolves into the liquid and, if the container is sealed, builds up pressure inside the carton or bottle. That’s why you might also notice the container looks swollen or puffed out before you even taste anything. Certain bacteria, particularly species of Leuconostoc and Lactobacillus, can also produce large volumes of CO2 during fermentation and contribute to blown packaging.
Why It Tastes and Smells Different
Fizz isn’t the only change fermentation brings. As microbes break down the juice’s sugars, they generate a range of byproducts that alter both flavor and aroma. These include acetic acid (the sharp tang of vinegar), various esters and alcohols that can give the juice a boozy or solvent-like smell, and ketones that add unfamiliar off-flavors. Lactic acid fermentation specifically produces compounds like diacetyl, which has a buttery taste that doesn’t belong in orange juice.
If your juice smells yeasty, sour, or faintly alcoholic alongside the fizz, those are all signs that fermentation is well underway. The more pronounced these flavors are, the further along the process has gone.
How Much Alcohol Develops
Even normal, fresh orange juice contains trace amounts of ethanol from natural fermentation, typically between 150 and 900 parts per million. That’s well below the 0.5% alcohol by volume threshold used to classify a drink as non-alcoholic. However, once active fermentation takes hold, alcohol levels can climb significantly. In one study of orange juice with added sugar left to ferment spontaneously, the alcohol concentration reached 12.2%, comparable to a glass of wine. Your forgotten carton in the fridge won’t reach that level quickly, but it illustrates how far the process can go if left unchecked.
Common Reasons It Happens
Several scenarios lead to carbonated juice at home:
- The juice sat too long after opening. Once you break the seal, you introduce oxygen and airborne microbes. Even refrigerated, yeast can slowly multiply and begin fermenting. Pasteurized juice that’s been open for more than about seven to ten days is increasingly likely to develop fizz.
- The juice wasn’t kept cold enough. Yeast activity accelerates at warmer temperatures. If the juice spent time on a counter, in a warm car, or in a fridge that isn’t holding below 40°F (4°C), fermentation can start faster than expected.
- The juice is fresh-squeezed or unpasteurized. Without pasteurization, the natural yeast and bacteria on the fruit’s skin survive in the juice. These products have a much shorter shelf life, sometimes only a few days, and are more prone to rapid fermentation.
- A sealed container was compromised. Damage to a carton or a loose bottle cap can allow contamination even before you officially “open” the product. In commercial production, spoilage by yeasts that survive pasteurization or enter through packaging flaws results in off-flavors and CO2 buildup that causes blown packages.
Is It Safe to Drink?
Carbonated orange juice is spoiled juice, and drinking it comes with real risks beyond the unpleasant taste. The problem isn’t just the yeast producing fizz. The same conditions that allow fermentation can also support harmful bacteria. Unpasteurized juices in particular have been linked to outbreaks involving E. coli O157:H7, Salmonella, and Staphylococcus aureus. The FDA requires unpasteurized juices to carry a warning label noting the risk of serious illness, especially for children, older adults, pregnant people, and anyone with a weakened immune system.
Even pasteurized juice that has started fermenting is no longer safe to rely on. The fermentation itself signals that microbial populations have grown beyond what the original processing controlled for, and you have no way to tell at home whether only harmless yeast is present or whether pathogenic bacteria have also multiplied. A sip or two is unlikely to cause serious harm in a healthy adult, but there’s no good reason to keep drinking it.
How to Prevent It
Keeping orange juice from going fizzy comes down to temperature and timing. Store it at or below 40°F (4°C) at all times, and minimize how long it sits on the counter while you’re pouring. Once opened, plan to finish pasteurized juice within seven days. Fresh-squeezed or unpasteurized juice should be consumed within two to three days, or frozen if you can’t use it that quickly.
Before buying, check the container for any signs of swelling, leaking, or damage. A carton that’s puffed up on the shelf has already started fermenting inside. If you notice fizz in juice you just opened for the first time, the product was likely contaminated before it reached you, and it’s worth returning it to the store.