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

By Paul Smart •  Updated: 03/14/21 •  6 min read

Why Does Red Cabbage Turn Into Blue Cabbage? 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 or the level of acidity or alkalinity. The color change of the cabbage is a result of a slight pH change 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 Cook Red Cabbage

There are a number of ways to prepare red cabbage, but the most common is to braise, pickle or just leave it raw. When working with cabbage it is common to shred it finely which is commonly done when making coleslaws or salads. As the majority of salad dressing contains acidic components it is rare that cabbage will turn blue.

However, when heat is applied to the cabbage the plant can start to turn blue as some of the acidic components are either boiled off during the cooking process.

How To Prevent Red Cabbage From Turning Into Blue Cabbage

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 which 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 as you are cooking it you will be able to return it to its original color by adding a small amount of vinegar or lemon juice.

Preparing Red Cabbage

To get the very best out of a red cabbage it is important to remove the outer leaves of the plant as they can become limp, lose their crunch, and even become discolored. The cabbage can then be cut the cabbage into quarters allowing the central stalk to be removed which can be a little tough. The cabbage should then be cut finely with a knife into a quarter of an inch strips

Cooking Cabbage

The method most commonly used to cook cabbage is braising or frying. The length of cooking can be used to determine the texture of the cooking. The longer the period of cooking the softer the cabbage will become. Additionally, the pigment within the red cabbage will be increasing transferred to other components in the dish the longer it is cooked.

This is generally most obvious when the other ingredients that are white. If you want to avoid this all together it is possible to use green cabbage instead as it has quite a similar taste.

Red cabbage can also be boiled. This method tends to soften the cabbage to a greater extent than frying or braising. To create a crunchier result add a teaspoon of salt and white vinegar for no more than a few minutes.

Another way to prepare the cabbage is to pickle it. This is a method that has been used widely for centuries in Europe to preserve the harvest. This technique also enables you to enhance the flavor of the cabbage.

The basic pickling method is quick and similar. Place the shredded cabbage into a sterilized jar. Pour the pickling solutions over the cabbage when it is still hot ensuring that the cabbage is completely submerged.

There are many variations of pickling brine that can be used which include a wide range of spices including mustard seeds, cloves chilli and ginger. However, the basic recipe I use is listed below

2 cups of Water

2 cups of white vinegar

1 teaspoon of salt

1 cup of sugar

Pour in a saucepan and bring it to the boil stirring as you go to dissolve the sugar. Once this occurs pour the pickling solution over the cabbage and seal it immediately. The cabbage will last for 12 months.

Growing Your Own Cabbage

In many regions, Red cabbage can be grown all year if different types of cabbage are used throughout the year. Red cabbage can be divided up into Spring, Summer, and Autumn cabbage based on the harvest time. The length of time that that the cabbage takes to mature varies from 90 to 150 days depending upon the variety.

To help identify the ideal variety visit our vegetable database page as it contains over 200 varieties.

In terms of growing, Cabbage is a hardy plant that tolerates temperatures as low as -3°C (26°F). Plants can be established by direct sowing into soil, however, planting in modular trays is recommended.

When sowing the seed it should be planted at a depth of 0.5 inches. The seedlings will typically appear after 7 to 14 days and usually take a further 4 weeks to become large enough to plant out in the garden.

Once the plants are large enough they can be planted out at a spacing of 50cms (20 inches), when the temperature is greater than 7°C (45°F).

To ensure that the seedling survives it is advisable to put snail pallets around to prevent attack. Apply a thick layer of mulch that is 2 to 4 inches thick and ensure that the seedlings remain moist throughout the growing season.

Paul Smart