Biofuel
Fuel in 99 Nights in the Forest
About
Biofuel is a fuel made only in the Biofuel Processor and used to keep the campfire alive. It is worth nearly twice a log and is not affected by rain.
Biofuel — In-Depth Analysis
Biofuel is a fuel item in 99 Nights in the Forest whose job is to keep the campfire burning. It cannot be found lying around: it only comes out of the Biofuel Processor, a machine you build yourself.
The processor costs 12 Wood and 12 Scrap. Once it is placed, you feed it and wait a short time while the input is converted into Biofuel. Any type of food works, such as carrots, and uncooked food is just as good as cooked food. Saplings, logs and most pelts are also accepted. Pelts are the more generous input, since they always yield more than one piece of Biofuel.
The main reason to bother is efficiency and reliability. A piece of Biofuel gives close to twice the fuel value of a log when added to the campfire. Logs can be hurt by rain, but Biofuel cannot, so it is a useful reserve for the moments when the fire is almost out at night, especially during a rainy one. In practice that means leftover food, spare saplings and pelts you do not need elsewhere can be turned into extra burn time instead of being wasted.
The wiki also jokes that the item looks like human feces, which is a fair description of its brown, lumpy icon.