The principal grape cultivar for juice is the Concord. It gives the dark purple anthocyanin color, the astringent-sweet flavor, odor, and other characteristics necessary for quality juice. Processing is similar to apple juice extraction except that a hot extraction is necessary to obtain the rich purple color derived from a complex mixture of anthocyanins. Grapes are gently washed with water sprays. Crushing takes place inside a perforated drum where rotating blades and beating bars break the grape’s skin but not the seeds and stems. The rotating blades produce a centrifugal action that forces juice and pulp through the slotted drum while the stems and some seeds are discharged out of the opening. The juice and pulp are extracted by heating at 60 – 63 ?C while being stirred with pectic enzymes in a steam-jacketed kettle. Heating time and enzyme concentration are adjusted to extract the desired color and solubles. Traditionally, juice has been pressed from the pulp using a plate and frame press. Hot pulp and juice are piled on a press cloth, which is folded to surround them. A second press cloth is placed on the first, and the process is repeated. About 50 % of the juice freely flows from the pulp before pressing. Hydraulic pressures of 1380 – 2050 kPa are used to complete the separation of juice, which may yield up to 90 %.
