Donald Qualls pages, Reinhold blog and Caffenol.org recipes.
Trying to get an overview, I putted all of them in a table and looked for some rule in these recipes. All of them use coffee and Sodium Carbonate as alkali, aka Washing Soda. Almost all the developers also use Ascorbic Acid, aka Vitamine C, but one uses only coffee, pure Caffenol. In this recipe the amount of coffee is twice the amont of soda and, depending on dilution, you get more or less time for it to work. It seems that the more coffee in proportion to soda, the more contrast you get. But pure caffenol will tend to give low contrast, grain and coffee spots. So, people give up soon developing only with caffenol and they try the other recipes with Vit. C that seems to work much better.
In all we can say that for one liter Caffenol, the recipes have following range of use, having all recipes in account:
Coffee - from 10 to 80 gBelow you can see two examples where in the first I used a developer based on just coffee as developing agent, in the second I combined coffee with another B&W developer, but not the usual Vit. C, but Acetaminophen, aka Paracetamol.
Ascorbic Acid - from 0 to 40 g
Sodium Carbonate - from 16 to 120 g
To make a better use of coffee in color developers, first I need to understand how it works in black and white photography. With this example it is clear that when you combne coffee with another well choosen developing agent, it works better, less fog and stains and not so grainy as only coffee. The amount of the other developing agent is minimal.