Is It OK To Drink Flat Soda? (What Happens)

You’ve grabbed a bottle of soda from the fridge, only to discover it’s flat – can you still drink it, or should you pour it away? When I was young, my mom always gave me flat cola for an upset stomach, so I assumed flat soda was OK to drink. Maybe it’s even better for you that way.

Flat soda is OK to drink for several days once opened if kept in the fridge to prevent bacteria growth. The loss of carbon dioxide will alter the flavor but it’s an unpleasant flavor, odor, and change of appearance that indicate spoilage.

A flat, unopened bottle of soda is still drinkable after 6-9 months, or longer if the container is stored well, as the soda is not perishable unless it has contacted the air.

Soda quickly loses its fizz once you’ve opened the bottle, and while some of us prefer the taste of a flat soda, others don’t. So does the carbonation make your drink taste better – or are we just used to the carbon dioxide? You’ll find this interesting if you’ve wondered what happens when drinking flat soda.

What Happens If You Drink A Flat Soda?

When you open a can or bottle of soda, the pressure on the dissolved carbon dioxide in your drink causes that welcome fizz of bubbles we all love. The bubbles are thanks to nucleation; the gas collects on imperfections in the glass and begins to gather together.

The longer your soda sits open, the more gas nucleates and escapes into the atmosphere.

As the levels of carbon dioxide drop in your drink, the fizz slowly disappears, and your soda goes flat. Some things can make your soda go flat even faster, such as pouring it over ice, stirring it with a spoon, or adding some sugar.

These methods work because either they create more nucleation sites for the bubbles to form or the movement agitates the soda so it can release more bubbles – one of the reasons a dropped bottle of soda goes flat so quickly!

But what happens when you drink this flat soda? Well, not much if you’ve just made it go flat—all you’ve done is remove the carbon dioxide gas. There will be no fizz, and the taste will be altered, but nothing bad will happen to you.

On the other hand, if you open a sealed bottle of soda and it’s already flat, you might want to look at the best-by date. The USDA says soda isn’t perishable, but flat soda months past its sell-by date is unlikely to taste great. If it’s 3-6 months past the expiry date, it’s probably better not to drink it.

Is It Better For You To Drink Soda Flat?

If you prefer the taste of flat soda – can that be better for you?

Well, it might reduce the amount of carbonic acid in your drink, but the sugars will still be there. The carbonic acid can build up in your stomach and cause bloating or heartburn, so drinking flat soda might be better for you if you’re prone to bloating or stomach aches.

If you prefer flat soda, drinking it will be no risk. For some people who find the bubbles leave a bad aftertaste or dislike the texture of the bubbles, drinking a flat drink will be more pleasurable.

Do you remember being given flat soda for an upset tummy – it was one way our parents tried to keep us hydrated when we were sick. I think it’s one of the reasons I’m not fond of flat sodas: it evokes memories of feeling ill and being in bed.

Well, it turns out this particular bit of home care is a myth. Of course, when our kids feel poorly and have a tummy bug, we’re concerned about them getting enough fluids.

Many parents convince a sick child to get enough fluid to avoid dehydration by offering them juices or flat sodas. Giving your sick kids an oral rehydration solution with the correct amount of sugar and electrolytes rather than a flat soft drink is better.

How Long Is Flat Soda Good For?

Flat soda is good for 3-4 days until the taste deteriorates and then you risk becoming ill from bacteria and other contamination in the air. It’s best to store it in the fridge to prevent this.

If the soda has no signs of spoilage – an unpleasant odor, taste, or color – then it is good to drink for several days. Discard when it goes off or it doesn’t taste good anymore.

As the carbonation decreases, some people may find they don’t enjoy the drink’s taste.

You can keep an unopened bottle of soda for three to six months past its listed expiry date, but after that, although it won’t harm you, it probably won’t taste very good. As long as the soda can or bottle is still intact, it’s unlikely that any contaminants will have entered the drink.

Once you’ve opened a bottle of soda, the gas will begin to escape and go flat faster.

Keep your soda as fizzy after you’ve poured a drink by capping it to retain as much remaining gas in the bottle as possible. Place the bottle back into the fridge, as keeping it cool will also help the carbon dioxide.

Most soda will stay fizzy for around 3-4 days once it’s been opened, as long as you don’t leave it uncapped.

As long as you don’t mind the taste of flat soda, you can still pour drinks from a bottle that has lost carbonation.

Why Does Carbonation Make Soda Taste Better?

So why do fizzy sodas taste better than flat sodas? Not all of us agree on that, and some people find that carbonation makes their drinks taste worse and even has an unpleasant aftertaste, but in general, most people say their drink tastes better with bubbles.

I prefer my drinks when they’re still fizzy, which made me wonder if the carbonation changes how the drinks taste or if it’s simply the texture of the bubbles that makes me think it tastes better.

The carbonation process creates a carbonic acid when added to water, which is a very mild acid with a slightly sour tang. When you sip sweet soda, your tongue is also picking up a delicious contrasting sourness from the carbonic acid, which most find very pleasurable.

Add to that the delightful tingle of bubbles against your tongue, and it’s clear the added carbonation provides an enjoyable sensation and enhances the pleasing tang of our sodas, making them taste better.

How to Keep Soda From Going Flat

To keep an unopened bottle of soda from going flat, keep it in a cool, dark place where the temperature will stay constant. Warm conditions will make the drink go flat faster as it’s easier for carbon dioxide to remain dissolved when it is cold.

The dark won’t affect the fizziness, but it’s a good idea to avoid light on your drink as it can cause chemical reactions that change the flavor and even the color of your beverage.

If you’ve opened your soda bottle, cap it tightly after use, and keep it in the fridge. Suppose you’ve opened a can and don’t want to drink all the contents at once; pour the rest into a glass bottle with a tight-fitting lid. Glass is better at preventing gas loss than plastic, as it’s less porous and usually has better seals.

For more tips on keeping your drink fizzy, check out my post on what makes soda go flat faster?


So is it OK to drink flat soda? Drinking a flat soda poses no danger to your health if it hasn’t spoiled, as the escaped carbon dioxide gas is not the main preservative. You can treat the drink like any other in terms of when it is sensible to throw it away.

If the drink is unopened, thanks to the sugar and acid content in most sodas, they are considered non-perishable, though the flavor deteriorates over time and with the loss of carbonation.

Tom Hambly

Tom Hambly is the founder of Totally Drinks. He loves to cook and drink nice things - his favorite drinks are wine, beers and whiskey. About Tom Hambly.

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