It is normal to boil water or porridge with purple potato, and the soup is blue-green. Because purple potato contains anthocyanin, which is a water-soluble pigment, it will change color when it meets acid and alkali, turn red when it meets acid, and turn blue-green when it meets alkali. Because the tap water we usually drink at home is generally alkaline, the color of the water for boiling purple potatoes is mostly blue-green.

Prevent the water boiled in purple potato from turning blue-green: just cook it without tap water, such as neutral boiled water. Or add a little acidic liquid such as white vinegar or lemon juice to make it turn purple again.

Extended data:

1. Purple sweet potato is rich in selenium and iron, which is an essential element for anti-fatigue, anti-aging and blood-enriching. In particular, selenium is known as the "king of cancer", so purple potato has anti-cancer effect and function.

2. Purple sweet potato is rich in cellulose, which can promote gastrointestinal peristalsis, keep defecation unobstructed, improve digestive tract environment and prevent gastrointestinal diseases.

3. Purple potato has slimming effect and function, which is a good choice for female friends to lose weight and eat purple potato. Eating purple potato will not only make you fat, but also help you lose weight, keep fit, prevent sub-health, relieve constipation and detoxify.

4. Purple sweet potato has the function of enhancing immunity. Purple sweet potato contains a lot of mucin, which can prevent the atrophy of liver and kidney connective tissue and improve immunity. Moreover, the minerals contained in purple potato play a very important role in maintaining and regulating human functions. Calcium and magnesium can also prevent osteoporosis.

Reference link: People's Network-What are the benefits of eating purple potatoes? Efficacy and function of purple sweet potato