12 BULLETIN 952, U. S. DEPARTMENT OF AGRICULTURE. 
perature, the optimum temperature for good commercial jelly being 
222° to 224° F. The housewife usually produces thinner jelly with 
a materially lower boiling point. In view of these facts it is apparent 
that it is not advisable to add too much water because of the pro- 
longed boiling which is necessary to remove it. 
Grape jelly foams exceedingly when it nears the jelly Sone and 
ample accommodations should be left to take care of the volume of 
foam. This is most readily accomplished by using a low-jacketed 
kettle and insuring ample steam pressure. 
Attention is also called to the fact that it is preferable to make 
the jelly in small quantities of 10 to 25 gallons rather than in 
quantities of 50 to 150 gallons, the common American practice. It 
is generally recognized that a product of higher grade can thus be 
obtained, since a smaller quantity means a greater percentage of 
heating area to the volume than is the case with larger quantities. 
This is due to the fact that as the quantity of liquid in a hemispheri- 
cal kettle is increased the volume increases as the cube of the radius, — 
while the surface exposed to the heat increases only as the square of 
the radius. Thus, there is a greater concentration of heat per unit 
of volume in the smaller quantity, with attendant quicker boiling. 
It may be of general interest to point cut that it is perfectly fea- 
sible to make good jelly by substituting some of the popular glucose 
sirups for granulated sugar. Such jelly, of course, is not as sweet 
as that made with the sugar, but this can be obviated by decreasing 
the quantity of tartaric acid added in the earlier stages or by using 
a mixture of equal parts of cane or beet sugar and glucose. It 
should be remembered, however, that commercial glucose contains 
approximately 30 per cent of water, and therefore a proportionately 
greater quantity by weight should ie used than of sugar. 
The phenomenon of crystallization attendant upon making grape 
jelly is one with which all housewives and jelly technologists are 
familiar. This is due to the slow precipitation of crystals of cream 
of tartar in the jelly during long standing, because of the insolu- 
bility of the crystals. Various means are used in the grape-jelly 
industry to obviate this. Some add alkali to the juice in order to 
convert the cream of tartar into potassium tartrate, which is more 
soluble in the jelly than the cream of tartar, and consequently there 
is much less tendency to crystallization. Others make jelly stock by 
boiling the grapes in a small quantity of water and canning the con- 
centrated product for future use. Upon standing, the crystals of 
cream of tartar slowly settle to the bottom, and when the time comes 
to make the jelly the juice can be poured off from the settlings 
(argols). By this means crystallization in the jelly is reduced to 
a minimum. 
