the extrusion-pressing process consists of the raw material characteristics. This comprises the seed moisture content and the typeof oilseed, but also the specific variety of the species and potentialdifferences in the seed and oil composition due to variations in thecultivation conditions. In contrast to single-screw extruder-presses,which are typically designed for a single oilseed species, twinscrew extruders show high process flexibility due to theirmodular design and may be employed for the thermomechanicalpressing of different types of oilseeds. This has been illustrated byAmruthraj et al. (2014), who have designed a twin-screw extruderpress which, through the installation of different barrel configurations, could serve as a means for efficient pressing of Pongamiapinnata seeds on the one hand, and as highly flexible R&D equipment for the processing of different oilseeds on the other hand.Even though no studies analyzing the varietal effect or the influence of cultivation conditions on the pressing process have beenreported for twin-screw extrusion so far, these parameters havebeen shown to exert a significant impact on the single-screwpressing process (Savoire et al., 2010; Zheng et al., 2003). As anexample, important differences were observed for the single-screwpressing of two varieties of flaxseed and were explained throughthe presence of a thinner hull for a particular variety, which rendersthe material more compressible and reduces its porosity fordrainage, thus leading to a reduced oil extraction (Zheng et al.,2003). The moisture content of oilseeds is of key importance tothe pressing efficiency of the process, as moisture acts as a lubricantand shows a large impact on the rheological properties of thecellular material inside the extruder. Many studies have describedthis effect for single-screw extrusion, where the general trendconsists of an increase in the oil extraction efficiency with areduction in the seed moisture content. This increase in efficiency isdue to an enhanced pressure build up with an increased seed rigidity, as shown for flaxseed (Zheng et al., 2003), rapeseed (Vadkeand Sosulski, 1988), crambe seed (Singh et al., 2002) and cupheaseeds (Evangelista and Cermak, 2007). The optimal seed moisturecontent for efficient thermomechanical pressing is largely dependent on the raw material and the operating conditions of theextrusion process, which are determinant for the degree of fill andinclude the pressing temperature, the screw profile, the seeds feedrate and the screw speed. While several studies have reported thepresence of an optimal moisture content beyond which theextraction efficiency no longer increases or even decreases, otherreports have found a continuous increase in oil recovery up to thepoint, often near a moisture content of 3e4%, where a furtherdecrease in moisture caused blocking of the extruder due to theexcessive pressure and friction of the very rigid material(Evangelista and Cermak, 2007; Singh et al., 2002). For example, anoptimal moisture content of 7% was observed for the single-screwpressing of rapeseed (Singh and Bargale, 2000) and linseed(Singh and Bargale, 1990), while other researchers reported amaximum pressing efficiency for rapeseed at 5% moisture content(Vadke and Sosulski, 1988) and for jatropha seeds, the optimalmoisture was found as high as 10% (Pradhan et al., 2011). Only onestudy has evaluated the influence of moisture on the performanceof a twin-screw extrusion-pressing process. For the extraction ofsunflower oil, sunflower seeds were conditioned to differentmoisture contents between 6 and 2% through oven drying prior totwin-screw pressing (Dufaure et al., 1999a). The authors found thata drying pre-treatment of the seeds led to important increases inthe foot content of the filtrate, for example from 10% to 25% for areduction in seed moisture content from 6% to 4%. Therefore, loweroil yields were obtained with intensively dried seeds due to thesignificant oil losses during centrifugation of the filtrate showing ahigh foot content, even though there was a decrease in the residualoil content of the press cake, indicating enhanced pressing capacity.