12 BULLETIN 952, V. S. DEPARTMENT OF AGRICULTURE. 



perature, the optimum temi^erature 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 point, 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 out 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 be used than of sugar. 



The phenomenon of crystallization attendant upon making grape 

 jelly is one with Avhich 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 jellj'' the juice can be poured off from the settlings 

 (argols). By this means crystallization in the jelly is reduced to 

 a minimum. 



