Fermentation is a chemical process where microorganisms break down sugars, generate heat, and releases gas bubbles, giving injera the tangy flavor similar to sourdough. It is a byproduct of depriving cells of oxygen. Bacteria and yeast not only thrive but produce energy in this environment. The organisms feed on sugar (glucose) and turn it into energy. Thus, when you do not feed the batter, the bacteria run out of sugars to digest and start to die, or alter their metabolism, which can cause the starter to turn dark or develop unusual aromas.
Alcohol is one of the byproducts of the process. That is why starters often have a strong acidic smell. The alcohol created during this process evaporates when the food is cooked but still gives it a robust and tart flavor.
Another byproduct is carbon dioxide (C02), which helps the batter grow during fermentation and rise when baking traditional bread in the oven.
The fermentation process is tricky. The environment needs to be just right for growing cultures to perform a series of reactions, making it challenging to recreate consistently. A controlled environment helps guarantee the best results.