Following extraction from biomass, biolipids can be used as pure oil (generally plant) or can be converted to biodiesel by a process known as transesterification, described later. However, the use of PPO as a fuel re­quires the modification of diesel engines unlike bio­diesel, which, particularly when blended with petroleum diesel, can be used in unmodified diesel engines. These engine modifications are needed as PPO is more than 10 times as viscous as biodiesel. As a result, it has a tendency to gum up in cold weather, which can be somewhat overcome by blending with traditional fossil diesel. Nevertheless, it has some advantages: with a flash point of over 300 °C, storage and transport are simplified. According to the VwVwS (Verwaltungsvorschrift wassergefahrdende Stoffe), which is the national German regulation on water hazard classification, PPO is not designated as even a hazard to water given that it is biodegradable. In an unmodified engine, poor atomization of the fuel will lead to coking of the injectors and accumulation of soot deposits. Modification is designed to preheat fuel or involves installation of a two-tank system. In the latter, the engine is started with diesel and only changes to PPO when the operating temperature has been reached. It must switch back to diesel before being turned off, to flush out the remainder of the PPO in order to ready the engine for the next operation. Other options exist, such as the specialist engine developed by Ludwig Elsbett in the 1970s. The fuel emissions of PPO are also much lower in sulfur emissions when compared to the fossil equivalent. For a detailed over­view see (Russo et al., 2012). After extraction, if the biolipid is not to be used as PPO, or other pure oil, it needs to be further processed into a more useable bio­fuel, usually biodiesel. Here the biolipid goes through a series of processing steps beginning with degumming.