1, use acidic or neutral water. Purple potatoes contain a lot of anthocyanin ingredients. Anthocyanin components will change different colors according to the degree of acidity and alkalinity, acidic water or neutral water cooked out of the purple potato porridge will be purple or red. Alkaline water is blue.

2, add white vinegar or lemon juice. When cooking purple potato porridge, you can add a small amount of white vinegar or lemon juice to prevent it from turning blue.