378 KEPOKT OF OFFICE OF EXPERIMENT STATIONS. 



to two seems to koop as well as that made with sii<::ar and juices one 

 to one. With the smaller amount of sup;ar the fruit flavor was more 

 prououncrd. In the tests undertaken to determine the effects of sufjar 

 added Ix'fore and after the cookini!; period, it was found that cane 

 su«j;ar cooked with apples wsis largely inverted; when added at the 

 close of the cookinjj; period, it was sli<;htly inverted; and although the 

 invert sugar is less sweet than cane sugar, yet the difference in sweet- 

 ness between stewed apples when the sugar has been added before and 

 after cooking, respectively, is so slight as to be of little practical conse- 

 quence. Edna D. Day" has also reported results of tests which have 

 to do with these (piestions and confirm Miss Snow's results. 



Nellie E. Goldthwaite, of the University of Illinois,'' has reported 

 results of an extended study of the chemistry and physics of jelly 

 making. According to Miss Goldthwaite, the essential things in fruit 

 juice are, first, pectin and, second, acid, a desirable constituent being 

 cane sugar, though jelly can be made without it. Too much sugar, 

 she concludes, is likely to cause a deterioration in the quality of jelly. 



The physical constants of hot juice ready to jelly on cooling are, substantially, 

 boiling point 103° C, and specific gravity 1.28. 



Jelly making seems to consist in so controlling conditions by means of acid and 

 sugar and boiling as to cause the pectin to be precipitated in a continuous mass through- 

 out the volume allotted to it. 



With respect to the necessity of the presence of acid in jelly making 

 a number of tests were carried on in which citric acid or tartaric acid, 

 organic acids which normally occur in fruit juices, were used in differ- 

 ent proportions. The results showed that with added acids it is 

 possible to make jellies of good texture from such fruits as peaches 

 and pears, though in the case of peaches the characteristic peach 

 flavor was not retained. 



At the Florida Experiment Station, Belling " studied guava jelly 

 making under a variety of conditions. According to his results, a 

 preliminary heating of the fruit is essential, as juice expressed from 

 the raw fruit did not flow readily, and though it gave a light, amber- 

 colored jelly with the proper proportion of sugar, with or without 

 citric acid, yet the characteristic guava flavor was entirely lacking. 

 The juices from heated fruit pass through the filtering cloth more 

 readily than that from raw fruit, and the heating also seems to help 

 in extracting the fruit flavor. 



The flavoring quality does not appear to reside in the oil glands of the rind. * * * 

 In the boiling of guava jelly some acid (the natural acid of the ripe fruit) is abso- 

 lutely necessary to change much of the sucrose into invert sugar, and if this does not 

 take place then the sucrose crystallizes out. Too much acid (and probably too pro- 



a Jour. Home Ecou., 2 (1910^, p. 94. 



b Jour. Indus, and Engin. Chem., 1 (1909), p. 333. 



c Florida Sta. Rpt. 1908, p. CV. 



