310 TECHNOLOGY OF CEREALS the hydrolysis of starch to glucose, and the mash liquefying enzyme is needed for the subsequent is then fermented with yeast, releasing carbon saccharification with glucoamylase. Ethanol yields dioxide gas, and producing alcohol. The wort is from wet-extruded and from steam-cooked grain treated with steam in a beer still, and the alcohol were almost equal, but the extrusion method uses is finally separated in a rectification column, less energy. Roller-milled whole barley, wheat or yielding 95% ethanol and leaving a protein- oats can be used in this process, with or without enriched residue, suitable for animal feeding the addition of thermostable alpha-amylase, which (Dale,1991) appears to have little effect during extrusion As a motor fuel, ethanol has various advantages cooking The fermentation stage is carried out over gasoline: it has a very high octane number; using either yeast( Saccharomyces cerevisiae) or the it increases engine power; it burns more cleanly, bacterium Zymomonas mobilis, the latter produc producing less carbon monoxide and oxides of ing an increased initial rate of fermentation(Linko nitrogen. On the other hand, there may be 1989a, b) difficulties in starting the engine on ethanol alone and accordingly a blend of ethanol with gasoline Furfural production from cereals Other uses for ethanol made from cereals. Corncobs the hulls of oats and rice, and besides motor fuel, include use as a solvent in fibrous parts of other cereals are rich in pentosans antifreeze and as the raw material for the manu- condensation products of pentose sugars, whicl facture of various chemicals, e.g. acetaldehyde, are associated with cellulose as constituents of ethyl acetate, acetic acid glycols(Dale, 1991). cell walls, particularly of woody tissues The carbon dioxide evolved during the fermen Thus, the pentosan content of oat hulls is given tation stage finds uses in oil fields, for recovery as 29%, along with 29% of cellulose and 16% of of additional oil, in the manufacture of methanol, lignin(McMullen, 1991). Pentosans are the start as a refrigerant and in carbonated beverages ing material for the manufacture of furfural,a (Dale,1991) chemical with many uses. Indeed, commercial A process for the continuous production of utilization of oat hulls and other pentosan- rich ethanol from cereals, involving screening, filter- cereal materials lies in the manufacture of furfural ing, saccharification, fermentation and distillation (MacArthur-Grant, 1986) tages,has recently been patented(Technipetrol Furfural was first produced commercially in SPA, 1989), while a dual-purpose flour mill has 1922. By 1975, oat hulls were providing about been described in which the four is air-classified 22% of the annual demand for furfural in the to produce a high protein fraction(particle size: U.S.A. but thereafter the demand for furfural 2-5 um) and a residual protein-depleted fraction and other furan chemicals far outstripped the for use as the starting material for production of supply of oat hulls, and increasing use was then Corncobs can be used for the production of hulls, corncobs, bagasse(Shukla, 1975. 2.rice ethanol (Bonnet and willm, 1989) made of other sources of pentosans, vi ethanol, and also of furfural (vide infra). By Plants for the commercial production of furfural treating the cobs with dilute sulphuric acid, 80% from agricultural residues have been established of the pentosans in the cobs are converted to in the U.S. A. The plant at Cedar Rapids, lowa pentoses, from which furfural is obtained, while uses oat hulls and corncobs; the one at Memphis the residual cellulose can be hydrolyzed to glucose tn uses rice hulls, corncobs and cottonseed in 65% yield(Clark and Lathrop, 1953) hulls; while the plant at Omaha, NB uses corn- Extrusion cooking has been suggested as a cobs only( Clark and Lathrop, 1953) method for pretreating grain to be used for the The commercial process for manufacturing production of ethanol. The thermomechanical furfural involves the boiling of the pentosan effects of extrusion cooking produce gelatinize- containing material with strong acid(sulphuric tion and liquefaction of the starch so that no or hydrochloric) and steam for 7-9 h at 70 psi310 TECHNOLOGY OF CEREALS the hydrolysis of starch to glucose, and the mash is then fermented with yeast, releasing carbon dioxide gas, and producing alcohol. The wort is treated with steam in a beer still, and the alcohol is finally separated in a rectification column, yielding 95% ethanol and leaving a protein￾enriched residue, suitable for animal feeding (Dale, 1991). As a motor fuel, ethanol has various advantages over gasoline: it has a very high octane number; it increases engine power; it burns more cleanly, producing less carbon monoxide and oxides of nitrogen. On the other hand, there may be 1989a,b). difficulties in starting the engine on ethanol alone, and accordingly a blend of ethanol with gasoline is generally used. Other uses for ethanol made from cereals, besides motor fuel, include use as a solvent in antifreeze and as the raw material for the manu￾facture of various chemicals, e.g. acetaldehyde, ethyl acetate, acetic acid, glycols (Dale, 1991). The carbon dioxide evolved during the fermen￾tation stage finds uses in oil fields, for recovery of additional oil, in the manufacture of methanol, as a refrigerant and in carbonated beverages (Dale, 1991). A process for the continuous production of ethanol from cereals, involving screening, filter￾ing, saccharification, fermentation and distillation stages, has recently been patented (Technipetrol SPA, 1989), while a dual-purpose flour mill has been described in which the flour is air-classified to produce a high protein fraction (particle size: 2-5 pm) and a residual protein-depleted fraction for use as the starting material for production of ethanol (Bonnet and Willm, 1989). Corncobs can be used for the production of ethanol, and also of furfural (vide infra). By treating the cobs with dilute sulphuric acid, 80% of the pentosans in the cobs are converted to pentoses, from which furfural is obtained, while the residual cellulose can be hydrolyzed to glucose in 65% yield (Clark and Lathrop, 1953). Extrusion cooking has been suggested as a method for pretreating grain to be used for the production of ethanol. The thermomechanical effects of extrusion cooking produce gelatiniza￾tion and liquefaction of the starch so that no liquefying enzyme is needed for the subsequent saccharification with glucoamylase. Ethanol yields from wet-extruded and from steam-cooked grain were almost equal, but the extrusion method uses less energy. Roller-milled whole barley, wheat or oats can be used in this process, with or without the addition of thermostable alpha-amylase, which appears to have little effect during extrusion cooking. The fermentation stage is carried out using either yeast (Saccharomyces cmevisiae) or the bacterium Zymomonas mobilis, the latter produc￾ing an increased initial rate of fermentation (Linko, Furfural production from cereals Corncobs, the hulls of oats and rice, and the fibrous parts of other cereals are rich in pentosans, condensation products of pentose sugars, which are associated with cellulose as constituents of cell walls, particularly of woody tissues. Thus, the pentosan content of oat hulls is given as 29%, along with 29% of cellulose and 16% of lignin (McMullen, 1991). Pentosans are the start￾ing material for the manufacture of furfural, a chemical with many uses. Indeed, commercial utilization of oat hulls and other pentosan-rich cereal materials lies in the manufacture of furfural (MacArthur-Grant, 1986). Furfural was first produced commercially in 1922. By 1975, oat hulls were providing about 22% of the annual demand for furfural in the U.S.A., but thereafter the demand for furfural and other furan chemicals far outstripped the supply of oat hulls, and increasing use was then made of other sources of pentosans, viz. rice hulls, corncobs, bagasse (Shukla, 1975). Plants for the commercial production of furfural from agricultural residues have been established in the U.S.A. The plant at Cedar Rapids, Iowa, uses oat hulls and corncobs; the one at Memphis, TN uses rice hulls, corncobs and cottonseed hulls; while the plant at Omaha, NB uses corn￾cobs only (Clark and Lathrop, 1953). The commercial process for manufacturing furfural involves the boiling of the pentosan￾containing material with strong acid (sulphuric or hydrochloric) and steam for 7-9 h at 70 psi