I'm trying to make Injera traditionally, without any starter, just teff flour (the white one) and water (tap water). I mixed it and left in a bowl, covered by dish towel, in my kitchen. After 60 hours I noticed the surface (just the surface) was grey with molds, something gone wrong! I'm investigating about the causes. First of all I live in central Italy, weather conditions are obviously different from Ethiopia. Maybe my kitchen is a too humid place? Could be something related to tap water (PH?)? Or maybe I let it ferment too long, as there were bubble even after 48 hours.. Any hints?
I haven't done injera yet but I make dosa which is similarly traditionally fermented and one of the most important factors to do this safely and effectively is temperature. My experience with dosa batter indicates that much lower than ~70F (~21C) really slows the fermentation down. I tried to find a more precise temperature recommendation and found a blog (Culinaria Eugenius) which recommends 30C (~86F) (and includes a really thorough walk-through, too).
I have a really good Ethiopian cookbook at home I can check later, but I don't know if it will have a precise temperature recommendation.
If your kitchen is on the cool side (and I hope it isn't a steady 30C for your sake :-) ), it may be helpful to ferment it in the oven. If you have a pilot light on a gas oven, that is enough heat to keep it warm enough, or if not, if you have an internal oven light you can turn on, that can be enough heat.
You would need to keep it out, covered, for some time first, though, as the oven is less hospitable to the wild yeasts you want to catch in the first place.
Your batter could have been ready after 2 days, although it will achieve a stronger flavor if you let it ferment longer.
Another recipe from Mesob Restaurant in NJ says that it can be anywhere from 2-6 days for it to complete fermentation, but for safety's sake, you really do want the fermentation to start quickly so that the good wild yeast can build up and get finished before anything bad gets a chance to take hold, especially in a humid environment that is friendly to such mold spores.
(Note, Mesob is a good restaurant and their injera is good, even if they do cut costs by mixing in other grains, so I trust their advice even though I haven't made it myself from this recipe.)
Regarding your current batch, another blog instruction for making starter says that you can simply remove the mold by skimming off the top. If there is enough alcohol in the mixture that may be safe, but I personally would be likely to throw it out and start over, which is what is generally recommended in answers to this question about sourdough starter.
Edit: None of my books say anything more useful than "room temperature" for fermenting. Most indicate that it should be ready in 2-3 days.
The way I make injera is simple. Make a batter teff and water. Once your batter or dough is done take half a liter of water and pour it over your batter or dough. Let it seat for 5 days. After 5 days, REMOVE the separated water and keep it aside. You will need it to cover the batter again once you done cooking. Mix well the batter without the excess water and cook. Add new teff flour to replace what you took to cook.
THe batter ferments UNDER the excess water.