Marcelle was making a big batch of feijoada and started the black beans soaking the night before we were going to have it for dinner. As she was preparing to pour off the blue/purple water they had soaked in I asked her to save some for me.
The dinner was delicious. And I decided that I'd see what colors I could come up with after dinner. In the picture below you can see the spectrum of colors obtained from my black bean juice with vinegar and baking soda.
|Black bean indicator: acidic on the left, neutral in the middle and basic on the right.|
If you want to get some indicator in 10 minutes instead of 10 hours you can soak the beans in 70% isopropyl alcohol. The alcohol will make a solution much faster.
|Acid, neutral, and basic forms of anthocyanins.|