Why Do Onions Turn Blue?

If you enjoy cooking onions, you may be wondering why onions turn blue after they have been cooked. This is a commonly asked question, as many people will automatically assume that something has gone wrong if their onions turn blue.

Especially as the majority of foods will change colors only when they have started to go bad. So you may automatically think that this is a bad sign and you shouldn’t eat those onions.

But there are actually plenty of instances where produce may change colors depending on the situation. Whether that be a temperature, environment, or the type of vegetable that has changed its color.

So there may be other reasons involved if a vegetable that you cooked has changed in color after you put it in the fridge. Keep reading to find out why onions turned blue and whether or not they are still safe to eat after the fact.

Why Did My Onions Turn Blue?

If you cook red onions and they turn blue, you may be wondering why this happened. Red onions often turn a shade of blue after being cooked and stored in the fridge due To an alkaline reaction that the onions have.

onion and garlic

This is actually quite a common reaction that purple produce has after it has been cooked. So you may actually notice this happening with other purple produce like purple cabbage, as that can often turn blue as well.

You may assume that this means that your red onions have gone bad before you were able to eat them. But this is a normal occurrence and is nothing to worry about, as the red onions are still perfectly safe to eat.

They simply had a chemical reaction once they were cooked and stored away, resulting in the purple color turning blue. It may be a vibrant blue, a light blue, or even a bluish-green color.

Either way, this does not indicate that the onions have gone bad or are not safe to eat. As long as they have not been in the fridge for very long, they are still fresh and perfectly safe to consume.

They may just not look as nice, which is why some people prefer to cook their red onions as they eat them. Instead of storing them in the fridge where they can become discolored.

You Can Eat an Onion That Has Turned Green

If you have an onion that has started to turn green, you may be concerned about it and think it is not safe to eat. But the good news is that this is most likely nothing to worry about, and you can still eat that onion.

Onion on the table

White onions and yellow onions specifically can start to take on a greenish shade if they are exposed to sunlight. This has a chemical reaction and can create a green color on a perfectly healthy onion.

You may even cut open an onion defined that some of the layers inside have a greenish color to them. This is usually nothing to worry about either as long as they are not very soft or slimy, which would indicate that they have gone bad.

So when it comes to onions, color changes are not extremely uncommon and usually do not mean that the onion has gone bad.

Is It Normal for Onions to be Discolored?

You may be worried about your onions if they start to look discolored. Many people may think that this indicates they have gone bad or cannot be eaten anymore.

But discoloration can also indicate different things, not necessarily that the onion has gone bad. So it is useful to understand why onions may be discolored so that you do not throw them out if they are still perfectly edible.


Many onions will change in color if they have been bruised along transportation or after you got them home. This is especially true for onions with thin skins, as they do not have as much protection.

You will notice bruising if certain patches on the onion are much darker than the rest of the onion. For white or yellow onions, this will often look tan or brown in color, while red onions will have much darker spots.

These discolored areas can be cut off, and the rest of the onion can be used as normal.

Chemical Reaction

Onions are very susceptible to having chemical reactions depending on the environment and what temperature they have been put into. Which is why red onions can’t turn blue if they were cooked and then put into a cold environment like a fridge.

Chopping Onions

Red onions will also turn a much brighter and redder shade of purple when they are cooked with an acid. So if you cooked red onions with vinegar or lemon juice, they would take on a much more vibrant appearance as a chemical reaction.

Light Reaction

Onions can also react to light, as excessive sunlight can make a white or yellow onion start to develop a green tinge. This indicates that those parts of the onion have started to create chlorophyll and reaction to the sunlight.

You can still eat the onion, and you can even eat the green part if you like as there is nothing wrong with them.

In Conclusion

If you cooked red onions and they turned blue, these are still safe to eat as this was merely a chemical reaction. Chemical reactions are very common in onions, and you may even notice your red onions becoming more vibrant in some cases.

It is even normal for onions to turn green or have brown spots, depending on the situation.