2.3 Cassava feedstock preparation
2.3.1 Cassava chip
Similar to bioethanol production of corn grains, there are two processes for preparing
cassava chips which are “Dry Milling” and “Wet Milling”. In Dry Milling process (Figure 2),
chips are transferred to the hopper and a metal and stone detector. The chips are then milled
and sieved to obtain fine powders. Coarse powders are remilled. The fine powder having all
components including fibers is slurried with water and proceeds to cooking and enzyme
hydrolysis. The heat to cook slurry for liquefaction process is usually from direct steam
instead of a jet cooker due to the difficulties of handling particles and contaminants in
slurry. Owing to contamination of sand, conveyor system and grinding system require
special treatment. Furthermore, after passing through syrup making process, an extra
separation unit or hydrocyclone is required to remove sand and other impurities. The dry
milling process is suitable for batch fermentation. Most of existing factories in China and
some factories being installed in Thailand apply this dry milling process as it uses less
equipment and investment (Sriroth & Piyachomkwan, 2010b).
As corn grains are composed of many valuable components including protein, lipid and
starch, wet milling process has been developed as a separation technique in order to
fractionate starch and other high-valued products including corn gluten meal with high
protein content, corn gluten feed and corn germ for oil extraction. The grains are initially