I had many conversations about coloured food with my friends who are also chefs or food bloggers. Many of them say that they never feel attracted to blue or pink foods that should not naturally be that way. I get it, when I see a vegan burger in an artificially dyed green bun, I start wondering what has gone wrong with the human kind…
But what if it was coloured with 100% natural pigments from plants? I honestly don’t mind blue, purple or pink noodles, as long as they are naturally dyed. On the contrary, I think they are super fun if you understand the process behind it. As long as it tastes good, why not!
The secret ingredient – anthocyanins!
I first encountered the wonderful ability of anthocyanins from red cabbage to act as a pH-indicator back in elementary school, at a chemistry competition. Since then, I had occasionally been playing with it and used it for some small projects such as dyeing fabric and other things.
That was fun but relatively useless since the colour would turn out pretty light and would wash out easily (compared to some other plant dyes) if the fabric was not treated with some kind of mordant. Still, it was satisfying to watch the colour change in different pH conditions and I am sure this would make an interesting experiment to do at home with kids.
Using these plant pigments as a food colouring was a logical next step, right? The colour doesn’t need to be that lasting since you will eat it anyway, and it provides such a nice effect on a plate when you treat these pigments with solutions of a different pH.
How does nature do it?
Anthocyanins are water-soluble pigments from the phenolic group, that give some plants their blue, purple, pink and red colour. Some of the foods containing anthocyanins are red cabage, purple sweet potatoes, blueberries, blackberries (and many other berries), aubergine, black rice, red wine grapes…
When they are in pH-neutral conditions, these pigments appear blue to purple. In acidic conditions they will be pink (and provide a more stable colour), and when placed in an alkaline solution, they will turn turquoise to green.
This phenomenon appears due to pigment molecules’ different light absorbing and reflecting properties when in different forms that occur as a result of a different pH value. There is another fun thing about it – the reaction in which these pigments change form is actually reversible, so you can change the acidity of the same solution over and over again to get different colours.
Always a fun lunch idea
I did this experiment with my friend’s kids and they loved it! I used butterfly pea, as this plant contains LOTS of anthocyanins. We brewed a herbal tea with it, and then added lemon juice, little by little, to see it gradually change colour from blue to pink.
Butterfly pea tea is also super healthy and refreshing due to its high content of anthocyanins and other plant chemicals, so besides its beautiful colour, you can also get a nice refreshment.
Of course, if you would like to make this experiment with your kids and can’t find butterfly pea flowers where you live (I actually got mine in Thailand and Laos where they naturally grow), you can always do it with red cabbage. It will need to be cooked for some time and you will need a bigger quantity to have it turn out amazing, but it is worth the effort!
On the pictures below, you can see how it turned out for me when I dyed rice pasta with butterfly pea tea, in comparison to red cabbage. Both work great, but it is easier to get a vibrant colour with butterfly pea.
Nevertheless, I will write a recipe with red cabbage, because it is so easily available in most parts of the world. With butterfly pea it is easy – just brew the tea and soak or cook rice pasta in it. With red cabbage you will need a couple of extra steps, and here is how to do it.
- 120 g rice pasta
- 1/2 red cabbage
- 700 mL water
- a pinch of salt
- 1 tbsp apple cider vinegar or lemon juice + 50 mL water (acidic)
- 1/8 tsp bicarbonate of soda (baking soda) + 50 mL water (basic)
- Chop the cabbage into small pieces and put them into a pot.
- Add the water and put it on the stove.
- After it boils, cook for 3-5 minutes and then add the rice pasta.
- Cook for another 6 minutes or until the pasta is cooked. If you are using thin rice noodles, they will not need to be cooked - just soaked for 5 minutes.
- Drain it and remove the cabbage pieces.
- In one bowl, mix water and vinegar, and in another mix water and soda.
- Leave one-third of the pasta as it is (at this stage it will probably look pastel purple/violet); add another third into the vinegar solution and put the last third into the soda solution.
- Mix it a bit and leave until the colour has completely changed. The rice noodles that you mixed with vinegar or lemon juice should be pink, and the one in alkaline bicarb soda solution should be bright blue to turquoise, depending on the amount of alkaline solution that you used.
- Season with some tamari and serve with lots of fresh veggies to make it a super tasty, light lunch.
If you would like to get a complete colour gradation from bright pink through purple, violet and blue to turquoise, you can dilute some portions of the acidic and alkaline solutions with water and use them to get a variety of colours based on different acidity.