32 
BULLETIN 1158, TJ. S. DEPARTMENT OF AGRICULTURE. 
To produce clear sirup, evaporate crude sirup to 60° Brix or above, 
let it cool and stand for about 40 hours, then dilute it to 45° Brix 
with cold water containing kieselguhr, filter, and reevaporate. 16 
GENERAL PROPERTIES OF SWEET-POTATO SIRUP. 
Sweet-potato sirup is clear and has an amber color. The taste is 
sweet, with a slight distinctive flavor and a slight after taste. It 
is not as sweet as cane sirup, honey, etc., which are characterized by 
high proportions of sucrose or invert sugar. 
COMPOSITION OF SWEET-POTATO SIRUP. 
The analvsis of a sample of the sirup made at Fitzgerald is given 
in Table li. 
Table 11. — Chemical composition of sweet-potato sirup. 
Determination. 
Water- 
free 
basis. 
Solids (by specific gravity) (per cent). 
Ash (per cent) 
Protein (N x6.25) (percent) i 
Direct polarization ( °V.) 
Invert polarization (°V.) 
Reducing sugar as invert (per cent ) 2 . 
Reducing sugar as maltose (per cent) 
Total sugar as invert (per cent ) 2 
Sucrose by polarization (per cent ) 
Sucrose by reduction (per cent) 
Dextrin (per cent) 3 
1.63 
1.65 
57.94 
14.96 
14.96 
19.95 
1 Analysis made in the nitrogen laboratory of the Bureau of Chemistry. 
2 Munson and Walker method. The cuprous oxid on ignition gave over 98.5 per cent of cupric oxid, 
showing that it was nearly pure. 
» By fermentation method described in J. Assoc. Official Agr. Chemists, Methods of Analysis (1916), 
p. 179. 
Sweet potatoes contain very little dextrose or levulose, and practi- 
cally no inversion of the sucrose present occurs during sirup making. 
For these reasons a much better idea of the composition of the sirup 
is given by the application of the usual methods of analysis than 
would otherwise be the case. Thus, this analysis shows that the car- 
bohydrates of the sirup are mostly maltose (57.94 per cent of the 
sirup solids), dextrin (19.95 per cent of the sirup solids), and 
sucrose (14.96 per cent of the sirup solids). 
COMPOSITION OF SWEET-POTATO POMACE. 
The chemical analysis of the dried sweet-potato pomace, deter- 
mined by the cattle-food laboratory of the Bureau of Chemistry, is 
given in Table 12. 
16 One of the most difficult problems was the development of a simple method whereby 
a sirup which would be clear and would remain so on cooling and standing could be 
produced. The suhstance which gave most difficulty was a salt of unknown composition 
which separated out in minute quantities in the finished filtered sirup, thus rendering it 
turbid. This difficulty could be overcome by concentrating the wort to about 60" Brix 
and letting it cool and stand for at least 40 hours. During this time enough of the salt 
separates in the sirup so that by diluting it with cold water to about 45° Brix, filtering, 
and reevaporating to final density the sirup will remain clear on cooling and standing. 
