Why Do Onions Turn Blue? How to Check & know?

Why Do Onions Turn Blue? How to Check & know?

Did you know or wants to know that Why Do Onions Turn Blue? If you enjoy cooking with onions, you may be wondering why they become blue after cooking. This is a frequently requested issue since many people assume that if their onions turn blue, something is amiss.

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Why Do Onions Turn Blue? How to Check & know?
Why Do Onions Turn Blue? How to Check & know?

Especially since the bulk of foods only change colour when they begin to spoil. So you might believe that this is a negative sign and that you shouldn’t eat those onions.

However, there are numerous situations where produce may change hue based on the situation. It could be the temperature, the surroundings, or the sort of vegetable that has changed colour.

So there could be other causes if the colour of a cooked vegetable changes after it is refrigerated. Continue reading to learn why onions became blue and whether they are safe to consume thereafter.

What Caused My Onions to Turn Blue?

If you cook red onions and they turn blue, you might be wondering why. Due to an alkaline response that red onions have, they frequently turn a shade of blue after being cooked and stored in the fridge.

This is a rather frequent reaction to purple produce after it has been cooked. As a result, you may notice this happening with other purple produce, such as purple cabbage, which can often turn blue as well.

You might think that this means your red onions went rotten before you could eat them. However, this is a common occurrence and nothing to be concerned about, since the red onions are still totally fine to consume.

They merely underwent a chemical reaction after being cooked and stored, resulting in the purple tint turning blue. It could be a bright blue, a mild blue, or even a bluish-green.

In any case, this does not imply that the onions have gone bad or are unsafe to eat. They are still fresh and absolutely safe to eat as long as they haven’t been in the fridge for too long.

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Some individuals like to fry their red onions as they eat them because they don’t look as beautiful. Instead of storing them in the refrigerator, where they can discolour.

An Onion that has turned green can be eaten.

If you have an onion that has begun to turn green, you may be afraid that it is unsafe to consume. But the good news is that you shouldn’t be concerned, and you can still eat that onion.

When exposed to sunlight, white and yellow onions, in particular, might begin to turn a greenish colour. A chemical reaction occurs, resulting in a green tint on a completely healthy onion.

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You can even chop up an onion if parts of the layers within are greenish in hue. This is usually not a problem as long as they are not excessively soft or slimy, which indicates that they have gone rotten.

Color changes in onions are relatively unusual and usually do not indicate that the onion has gone bad.

Is it normal for onions to get brown?

If your onions begin to yellow, you should be concerned. Many individuals may believe that this means they have gone rotten or are no longer edible.

However, discoloration might signal a variety of causes, not just that the onion has gone bad. So understanding why onions may become discoloured will help you avoid throwing them out if they are still completely edible.


Many onions will change colour if they are harmed during transportation or after you have brought them home. This is especially true for onions with thin skins, which lack protection.

If particular portions of the onion are noticeably darker than the remainder of the onion, this indicates bruising. White or yellow onions will have tan or brown spots, whereas red onions will have considerably darker marks.

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These discoloured parts can be removed, and the remainder of the onion can be utilised normally.

Reactions in Chemistry

Onions are particularly susceptible to chemical reactions depending on the environment and temperature in which they are placed. This is why red onions cannot turn blue after being cooked and then placed in a cold environment such as a refrigerator.

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When red onions are cooked with an acid, they become a much brighter and redder hue of purple. As a result of the chemical reaction, if you fried red onions with vinegar or lemon juice, they would become much more bright.

The Light Reaction

Onions can also respond to light, as too much sunlight can cause a white or yellow onion to turn green. This signifies that those onion portions have begun to produce chlorophyll and react to sunlight.

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You can still eat the onion, and even the green part, because there is nothing wrong with them.


If you cooked red onions and they turned blue, don’t worry; this was only a chemical reaction. Chemical reactions are prevalent in onions, and in some situations, you may see your red onions growing more brilliant.

Onions can even turn green or have brown patches depending on the situation.



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About Cuisine Cravings Team

Hello there! Cuisine Cravings Team is a group of people who are passionate about Kitchen Ideas that developed this website to educate people on the finest kitchen techniques. We publish articles that focus on basic and fundamental cooking ideas for all levels of chefs, from beginners to specialists! Our objective is to remove the guesswork out of meal preparation so you may worry less and enjoy more! Food is an important aspect of our life, and we are excited to share our knowledge with you!

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