I made a premix of the solutions:
50ml instant coffee + 350ml water
35ml Sodium Carbonate + 350ml water
5ml Ascorbic Acid + 350ml water
10 minutes before I process the film, I mixed 100ml of each of the premixes, making 300ml of solution.
You can see a more detailed explanation on my blog http://camarasclassicas.blogspot.com/2010/10/caffenol-c.html