Why Does Red Cabbage Turn Blue? And Is It Safe To Eat?

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Is Blue Cabbage Safe To Eat? If you have ever cooked with red cabbage in a stir fry or used it in a salad, you might have had the experience of finding that the cabbage has turned by blue the following morning. This may look a little strange and somewhat disturbing but is it still safe to eat?

Red cabbage that has changed color overnight from red to blue is safe to eat. Red Cabbage along with other purple fruit and vegetables such as blueberries and purple carrots contain a group of compounds called Anthocyanins which change color with pH. The color change of the cabbage is a result of a slight pH within the food that is not detrimental to you or the flavor of the dish.

The Anthocyanin dye can be extracted by cutting the cabbage into small pieces and placing them in boiling water for 5 to 10 minutes. The solution produced can be used as a pH indicator. The picture below shows what happens to the color of the dye as the pH changes and helps explain the color change.

The pH of fresh Red Cabbage is usually between 6.0 to 6.5 which produces a purple color. An increase in pH to 6.5 or 7.0, which is the same as tap water, will produce a blue color.

How To Prevent Red Cabbage From Turning Blue

To avoid the appearance of blue cabbage all that is required is the addition of an acidic substance which could include vinegar, lemon juice, lime juice or even things like soya sauce are also acidic. The volume required of the acidifying agent is relatively small, 1/2 tablespoon of the ingredient is usually more than enough. For recipes that already contain acidic components, you will not need to add any additional quantities.

Additionally, the reaction that causes the discoloration of the cabbage is reversible. This means that if the dish you are cooking does happen to turn blue you will be able to return it to its original color by adding a small amount of vinegar or lemon juice.

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