It would be manifestly impracticable, as a rule, to remove even the seeds of small fruits, except where jelly is to be manufactured. The fruits, having been properly prepared, are mixed with sugar or thick sugar sirup and subjected to heat for two purposes. The first purpose of heat is to sterilize completely the material so that no bacteria, germs, or spores may be left alive in the finished product. The second purpose of heating is to concentrate the material to a proper consistence and to thoroughly saturate all portions with sugar sirup. Incidentally, the heating also by the combined action of temperature and free acids in the fruit inverts a large quantity of the cane sugar that is used and thus prevents the finished product from granulating. The crystallization of the sugar in these bodies renders them very much less desirable and suitable for consumption. For this reason, among others, the precaution above mentioned, namely, that the fruit should not be overripe, should be observed. It has been seen that overripe fruit diminishes in acidity, and hence it is less suitable for converting the cane sugar than fruit just short of complete maturity. For this reason, too, the more strongly acid fruits are better suited for making these sweetened products than those in which the acidity is less strongly developed.
Jams.
—As has already been said, jams differ from jellies in that they contain not only the juice of the fruit but the whole pulp of the fruit or the whole fruit. The methods of preparation in effect produce the same changes upon the sugars that are produced by the fruit juice. The fruit after proper comminution is boiled with large quantities of sugar a sufficient length of time to reduce the fruit flesh to a pulp and to invert more or less of the sugar which is used. The insoluble matter which jam contains consists chiefly of the cellulose and pectose matter in the fruit, together with the seeds of the small fruit. The various solids are made up of the solid bodies in the fruits, including the sugars which are added. The character of the ash of the jams is a good indication whether or not they are pure, that is, made out of sugar and fruit only. While it is true that the ash of fruit varies, it is also true that the real ash of fruit has certain characteristics in regard to alkalinity which are not possessed by the ash of adulterated fruit products. For the sake of convenience and reference it is seen advisable to append a table showing the composition of the ash of some of the fresh fruits (Bulletin 66, Bureau of Chemistry).
| Fruit. | Pure Ash. | K2O. Potash. | Na2O. Soda. | Lime. | P2O5. Phos- phoric Acid. | SO3. Sul- furic Acid. | Cl. Chlorin. |
|---|---|---|---|---|---|---|---|
| Percent. | Percent. | Percent. | Percent. | Percent. | Percent. | Percent. | |
| Apple, | 0.264 | 55.21 | 11.69 | 4.79 | 12.83 | 4.62 | 0.83 |
| Apricots, | .508 | 59.36 | 10.26 | 3.17 | 13.09 | 2.63 | .45 |
| Banana, | 1.078 | 63.06 | 2.34 | .86 | 1.62 | 2.32 | 26.93 |
| Cherries, | 0.440 | 57.67 | 6.80 | 4.20 | 15.11 | 5.83 | 1.83 |
| Figs, | .682 | 57.16 | 2.38 | 10.90 | 12.76 | 3.90 | 2.05 |
| Grapes, | .500 | 50.95 | 6.32 | 4.96 | 21.27 | 4.28 | 1.54 |
| Lemons, | .526 | 48.26 | 1.76 | 24.87 | 11.09 | 2.84 | .39 |
| Oranges, | .432 | 48.94 | 2.50 | 22.71 | 12.37 | 5.25 | .92 |
| Prunes, | .486 | 63.83 | 2.65 | 4.66 | 14.08 | 2.68 | .34 |
From the above table it is seen that there is not a very large percentage of sulfuric acid in the natural ash in fruits, and very little chlorin, with the exception of the banana, in which the ash is principally potassium chlorid. Since the ash of glucose, as it is made at the present time, consists almost entirely of sulfates and chlorids, any considerable increase of these ingredients of an ash over the normal may be regarded as an indication that the fruit product from which the ash is obtained contains added glucose. Inasmuch as there are chemical and physical methods of detecting glucose which are entirely reliable, the utility of the composition of ash for this purpose is rather confirmatory than otherwise. Since the added sugar is the chief constituent of jams there is little difference in other respects in the composition of jams made from different fruits, as will be seen by the table of analysis given below:
| Description. | Total Solids. | Acidity. | Reducing Sugar. | Cane Sugar. | Total Sugar. |
|---|---|---|---|---|---|
| Jams. | Percent. | Percent. | Percent. | Percent. | Percent. |
| Apple, | 63.22 | 0.282 | 25.52 | 29.11 | 54.63 |
| Blackberry, | 55.42 | .851 | 18.77 | 29.00 | 47.77 |
| Grape, | 56.64 | .744 | 33.44 | 11.33 | 44.77 |
| Orange, | 80.52 | .433 | 13.61 | 54.23 | 67.84 |
| Pear, | 61.52 | .163 | 13.20 | 33.74 | 46.94 |
| Peach, | 65.65 | .500 | 36.48 | 23.16 | 59.64 |
| Pineapple, | 73.92 | .314 | 14.05 | 46.40 | 60.45 |
| Plum, | 50.43 | 1.012 | 28.29 | 9.70 | 37.99 |
The characteristics of fruit which give the special flavors to the jams are imparted by constituents such as ethers, essential oils, and other aromatic substances, together with the free acids which are present in such quantities as not to be susceptible of easy quantitative determination by chemical means. The relation which exists between the cane sugar and the invert sugar is not a safe index of the method of preparation, but is rather an indication of the excess or deficiency of the acid in the fruit employed. The greater the quantity of active acids, other things being equal, the larger the quantity of inverted sugar and the smaller the quantity of cane sugar in the finished product.
In the following table is given the composition of a number of jams made in the laboratory of the Bureau of Chemistry. These analyses are selected from a great many which are available because the character and amount of sugar in the composition of the jam were carefully controlled, and thus the chemical data afford a base of direct composition.
| Se- rial Num- ber. | Descrip- tion of Sample. | Total Solids. | Ash. | Total Acids Ex- pressed as H2SO4. | Pro- teids (N × 6.25). | Sugars. | Polarizations. | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Re- ducing sugar. | Cane sugar added. | Cane sugar found. | Cane sugar inverted. | Direct at 18° C. | Invert at 18° C. | Invert at 86° C. | |||||||||
| P. ct. | P. ct. | P. ct. | P. ct. | P. ct. | P. ct. | P. ct. | P. ct. | °V. | °V. | °V. | |||||
| 20446 | Apple (fall pippin) | 63.22 | 0.20 | 0.282 | 0.175 | 25.52 | 51.31 | 29.11 | 43.22 | + | 26.3 | - | 13.0 | + | 4.8 |
| 20414 | Blackberry | 55.42 | .48 | .851 | .737 | 18.77 | 43.99 | 29.00 | 34.08 | + | 24.6 | - | 14.6 | + | 1.6 |
| 20445 | Grape (fox) | 61.80 | .19 | .698 | .200 | 50.06 | 54.21 | 3.70 | 92.96 | - | 9.0 | - | 14.0 | + | 2.2 |
| 20416 | Grape (Ives seedling) | 56.64 | .48 | .744 | .525 | 33.44 | 42.45 | 11.33 | 73.38 | + | 3.5 | - | 11.8 | 0 | |
| 20443 | Orange (Florida navel) | 80.52 | .44 | .433 | .944 | 13.61 | 69.13 | 54.23 | 21.55 | + | 55.9 | - | 17.5 | + | 2.0 |
| 20448 | Pear (Bartlett) | 61.52 | .28 | .163 | .312 | 13.20 | 46.52 | 33.74 | 18.87 | + | 32.3 | - | 13.2 | + | 1.0 |
| 20442 | Pineapple | 73.92 | .30 | .315 | .312 | 14.05 | 60.20 | 46.40 | 22.90 | + | 52.3 | - | 10.3 | + | 6.2 |
| 20421 | Plum (damson) | 50.43 | .54 | 1.102 | .525 | 28.29 | 37.75 | 9.70 | 74.42 | + | 3.1 | - | 10.0 | + | 1.2 |
| 20423 | Plum (wild fox) | 62.10 | .46 | 1.355 | .212 | 28.78 | 47.86 | 23.26 | 53.43 | + | 13.9 | - | 17.5 | 0 | |
The following table represents the data relating to the composition of jams from samples purchased in the open market, free from glucose and apparently pure: