I guess... You can regrow coal/trees in this case, or meat and neck that was cooked to long. Could be one opinion for 2 coal - 1 ore. And from my experience Sometimes I have 1 coal left and sometimes 1 ore left in the smelter. I don´t know how the process is counting but it works in some ways.

Buuuuuuut it would be nice by holding "E" loading to full charge at once.