Before you go making faces wondering if I’ve lost my mind, rest assured that I haven’t just dumped blue dye into regular mashed potatoes. These blue mashed potatoes are essentially Colcannon, except instead of using regular cabbage, I’ve used red cabbage. The cabbage is cooked in milk to extract its color. Then the colored milk and cooked cabbage are mixed together with the potatoes after they’ve been mashed.
“But isn’t red cabbage magenta in color” you say? Well yes, but there’s a simple trick you can use to turn it blue. The pigment in red cabbage is pH sensitive and turns red when the pH is less than 7(acidic), while it turn blue when the pH is greater than 7(alkali). Milk has a pH of around 6.5, which means it’s slightly acidic, but adding a bit of baking soda will quickly increase the pH turning the milk a vibrant blue. The more you add the more blue your mashed potatoes will be, but you have to be careful as too much baking powder will give the mashed potatoes an unpleasant taste.
When mixed in with the mashed potatoes the blue cabbage and and milk give the potatoes a stunning color. Cabbage also contains a lot of glutamic acids which means it adds a ton of flavor as well. If you want to add even more, you could also add some blue cheese, which is my secret to making a great Irish Champ.
This blue cabbage trick can also be used to make a natural blue dye as well. Just boil the red cabbage in water instead of milk and then strain out the cabbage before reducing the liquid and adding the baking soda. As long as the food you add it to is not acidic, the dye will turn everything from rice, to pasta dough to bread a festive shade of blue.
Armed with this trick, try coming up with a natural red white and blue buffet for your next patriotic barbecue and have a Happy Fourth of July!
- Boil the potatoes skin-on until you can easily slide a toothpick through one.
- Slice the cabbage into thin strips and then add them to another pot, along with the milk and salt, and bring the mixture to a boil.
- Turn down the heat and simmer until the cabbage is very tender and the milk is a vibrant purple (about 20-25 minutes).
- Add baking soda a little bit at a time until the mixture reaches your desired shade of blue. Don't add more than 1/8 teaspoon though as too much will make your mashed potatoes taste metallic. Add the butter and melt.
- When the potatoes are tender, mash them.
- Add the blue cabbage and milk mixture to the potatoes and stir everything together until the blue mashed potatoes are creamy and uniform in color.