Both höfats bioethanol fuels are intended for product-specific use. This means that the SPIN 90 | 120 can only be filled with the gel fuel (black cap). The new SPIN 900 | 1200 | 1500 and all SPINs retrofitted with the new Bio-Burner 900 | 1200 can only be filled with the liquid fuel (green cap).
Under no circumstances should you fill the new Bio-Burner with the previous höfats bioethanol gel fuel, as this can cause damage.