6 BULLETIN 656, U. S. DEPARTMENT OF AGRICULTURE. 



CRUSHING AND STEMMING THE FRUIT. 



The crusher consists of two rollers of metal, usually bronze, revolv- 

 ing at high speed. The rolls are set in such a manner as to avoid the 

 crushing of the stems and seeds. The stemmer is a cylindrical re- 

 volving drum, inside of which are arranged revolving fingers that 

 separate the berries from the stems. The crushed berries and liber- 

 ated juice pass through openings in the side of the drum and fall 

 through to the cooker, while the stems are pushed out of the drum 

 by the fingers. 



HEATING THE CRUSHED FRUIT. 



From the stemmer the crushed fruit and the liberated juice fall 

 into the heating kettles, commonly called cookers. 



The grape berry may be divided into two main parts, the skin and 

 the pulp. The pulp of the grape is practically colorless and carries 

 most of the juice. The skin furnishes the coloring matter so much 

 desired by the manufacturer of Concord grape juice, as well as less 

 desirable ingredients. The juice of the pulp is sweet and pleasant 

 but lacks body and character. The juice from the skin is highly 

 colored, high in acid and tannin, and in mineral ingredients and 

 body, but low in sugar. By judiciously mixing these two juices a 

 better product, of more pleasing appearance, is obtained than would 

 result from either of these juices alone. 



Such a modified juice is obtained by the simple operation of heating 

 the crushed fruit to suitable temperatures. The very closest atten- 

 tion is required, however, to secure the best results. Temperatures 

 which are too high give the juice a harsh taste, lacking in quality but 

 high in coloring matter, and if carried to excess may ruin the flavor 

 and aroma completely. On the other hand, low temperatures do 

 not draw sufficient color, and such juices are wanting in body, though 

 pleasant in taste and aroma. 



In choosing the best temperature for heating the crushed fruit, the 

 quality of fruit must be taken into consideration. Ripe fruit or 

 fruit that has been air-ripened yields its desirable ingredients at a 

 lower temperature than immature fruit. Also the pressing process 

 must be considered in connection with the heating, as by applying 

 more or less pressure the color, tannin content, and body of the juice 

 may be regulated, the greater pressure giving the more color, tannin, 

 and body to the juice, as well as delivering the greater amount of 

 juice. It is apparent that to regulate the tannin content and the 

 body of a juice by using a smaller amount of pressure, means a loss 

 of juice. Consequently it is better to regulate the heating process 

 and not rely altogether upon the pressing process to correct the 

 quality of the juice. In this connection it should be said that 



