10 BULLETIN 1010, U. S. DEPARTMENT OF AGRICULTURE. 



practice among some refiners to roast the earth, while others claim 

 that the temperature used should be only high enough to remove 

 external moisture and that excessive heating affects the porous 

 character of the earth. Accordingly, three samples of oil were 

 bleached with earth treated as follows: (1) No dehydration, (2) 

 heated at 100° C. for 15 hours, and (3) roasted at high temperature 

 for five minutes. Table 4 shows the results. 



Table 4. — Effect of the degrees of dehydration on the bleaching efficiency of standard 



fuller's earth. 



Treatment of the earth. 



Color. a 



Yellow. Red 



No dehydration 



Dehydrated at 100° C. for 15 hours e 



Roasted at high temperature for five minutes. 



6 13.0 

 21.5 

 16.5 



1.1 



1.1 

 .9 



a Colors read in 2-inch cell. 



b Color of the oil before treating with earth: Yellow, 36.0; red, 4.0. 



e This treatment resulted in a 12 per cent loss in moisture. 



This experiment was repeated with almost identical results. Earth 

 previously roasted effected a slightly better bleach on the red but 

 somewhat poorer on the yellow, while earth dehydrated at 100° C. 

 appears to be the least beneficial, for reasons not yet apparent. It 

 appears, therefore, that better results are obtained on corn oil by 

 using fuller's earth as it is found on the market. 



Some oils can be more effectively bleached by means of a decolor- 

 izing carbon or a combination of such carbon with fuller's earth. 

 Four of the principal commercial decolorizing carbons were tested on 

 corn oil, alone and in combination with fuller's earth. The color 

 of the oils thus treated was so manifestly the same that no readings 

 were made, but the conclusion is warranted that the color in corn 

 oil is not removed to any practicable degree by these carbons. 



A further bleaching is effected during the deodorizing process. 



DEODORIZING. 



The process of deodorizing is the third and last principal step in 

 the preparation of an edible oil. The trade demands an oil which 

 is as nearly as possible without deleterious odor and taste, and it is 

 mainly to remove such odor and taste that this last process is neces- 

 sary. The treatment as followed at the present time has a further 

 value, however, in that it frequently effects a considerable bleaching 

 at the same time. 



The method employed in the deodorization of oils consists essen- 

 tially in blowing steam through the heated oil, usually under reduced 

 pressure. This removes all volatile constituents and leaves a bland 



