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AGRICULTURE HANDBOOK 495, U.S. DEPT. OF AGRICULTURE 



in baking. Flours prepared by such 

 techniques are often gray to black, 

 from mold growth and polypheno- 

 lic oxidation, and are not favored 

 except when fresh yams are not 

 available. 



With modern techniques a higher 

 grade of flour can be produced. In 

 an ideal process the yams would 

 be washed, lye-peeled, trimmed, 

 cut into pieces, dried with hot air, 

 ground into a fine flour, sieved to 

 appropriate size, and then pack- 

 aged. Laboratory experience shows 

 that the flour potential of D. alata 

 varieties differs. Pigments in the 

 flesh or a tendency towards poly- 

 phenolic oxidation results in off- 

 colored flours or unappetizing 

 odors or flavors. The best yams for 

 flour have fine, dense, perfectly 

 white flesh, the same varieties pre- 

 ferred for boiling and frying. 



In contrast to flours of other 

 farinaceous roots and tubers, yam 

 flours can be substituted for wheat 

 flours at a higher percentage, per- 

 haps as much as 60 percent. The 

 success of this substitution pos- 

 sibly is related to the high protein 

 content of the tubers or perhaps 

 to its mucilagenous character. 

 However, as the percentage of yam 

 flour increases, certain problems 

 are encountered, among them, poor 

 crumb quality and poor rising of 

 the dough. Taste panels have 

 judged products made from yam 

 flour, including pancakes, cup- 

 cakes, conventional bread, and 

 hard bread rolls, acceptable to 

 delicious. 



The nutritional value of yam- 



wheat flour mixtures needs study. 

 Since the protein content of the 

 two simple flours is about the 

 same, the total protein may not 

 change by combining them. Never- 

 theless, the relatively high lysine 

 content of yam flour and the com- 

 plementary content of methionine 

 in wheat flour should result in a 

 mixture of high nutritional value. 



The realistic use of yam flour 

 calls for a cookery based only on 

 it, not on a mixture of flours. Such 

 a cookery needs to be developed 

 not only for homemade flour but 

 also for commercially produced 

 and marketed flours. The potential 

 of yam flour in the processed-f ood 

 industry merits investigation. If 

 yam flour is to become widely used, 

 techniques to produce yams more 

 cheaply, probably through mech- 

 anization, need to be developed. 



COMPOSITION 



The dry weight of the edible 

 portion of the yam is about 15 to 

 35 percent of the fresh weight. 

 High dry weights are associated 

 with fine structure, dense feel, and 

 high quality. Maximum dry 

 weights are achieved near the end 

 of the dry season. High density is 

 a varietal character that is not 

 changed much by environmental 

 influences. 



The composition of five varieties 

 of D. alata was reviewed by Wilde- 

 man (table 3). Water is the chief 

 ingredient, of course, followed by 

 starch. The lowest starch figure, 

 15 percent, represents the content 

 of an immature tuber, and few 

 varieties would assay less. As a 



