An acidic rinse is a natural hair conditioner with a pH value < 7. Only natural ingredients that you can usually find in your household are used. One of the most well-known acidic rinses is the one with water and apple cider vinegar.
But I always suggest using citric acid instead, because it has a lower impact on the planet.
You can make your acid rinse with ACV by combining 1 tablespoon of vinegar in 1 glass of water (around 250/300ml). Once your hair is dry it will not smell at all, don’t worry!
Otherwise you can dilute 1 teaspoon of citric acid in 500ml of water.
Why should you really consider doing an acid rinse after using a saponified shampoo?
Tap water and hair soap used to wash your hair are alkaline with a pH value > 7, and might open the cuticle layer of your hair. Your scalp has a pH of about 5.5 and the acidic rinse after washing your hair, helps to reduce the pH value. As a result the cuticle layer of your hair closes again.
Your hair is easier to comb because your hair is smoother with closed cuticles.
The inside of the hair is better protected from drying out when the cuticles of your hair are closed.
Your hair shines when the hair cuticles are closed. On a smoother hair surface, light reflects better and this is perceived as shine.
Are you gonna give it a go?