It is possible to create a vat from indigo, lime (calcium hydroxide) and over-ripe fruit such as bananas or dates that relies on the chemistry of the sugars* rather than fermentation of the fruit. But it’s easier to simply use fructose shared in
Michel Garcia’s 1-2-3 recipe. It’s very simple: One Part indigo,two parts lime and three parts fructose, plus warmth.
*Fructose and glucose found in ripe fruit are reducing sugars; ordinary sugar – sucrose – is not a reducing sugar.