Grape Juice

The development of bulk storage of grape juice paralleled the experience with tomato juice, but the products are different primarily due to the higher sugar content and flavor lability of grape juice. The aims are similar. The "Concord" grape juice industry primarily in the eastern United States is used for juice, jams, jellies, and fruit juice drinks. The western U.S. grape industry is about 10 times as big and is used for wines, brandies, raisins, juices, and fruit juices. Both have a need for bulk storage of grape juice. Friedman (8) attributed the development of the Concord grape juice industry in the last 70 years to three major technological developments: (J) bulk storage of juice, (2) continuous processing, and (3) mechanical harvesting. Continuous processing was introduced about 1955 to replace the batch process being used by the apple and grape industry prior to that time. The batch process consisted of crushing the heated grapes and building a pad of grapes on a filter cloth on a wooden rack. The racks and layers of grapes were alternated to build a large pile and the whole stack was placed in a filter press to remove the juice. A number of types of continuous presses were developed that removed the juice in one pass. The batch process was labor intensive and slow, whereas the new presses enabled some plants to process 2000 tons of grapes per day. The introduction of mechanical harvesters, at approximately the same time as continous pressing, enabled the operators to harvest a large quantity of fruit in a short time. Most harvesters consist of a machine that straddles the row of grapes, and beater blades separate the grapes from the vine. The grapes are collected and transferred to a tank in the vineyards for transport to the processing factory. Today, nearly all grapes for processing are mechanically harvested.

A typical bulk storage operation would be as follows. Grapes are crushed and destemmed, heated to about 60°C, and treated for 30 to 40 min with a depectinizing enzyme to disintegrate the pulp and release the juice. A filter aid, usually a cellulose derivative, is added, and the skins and seeds are separated in a continuous press. The juice is filtered, flash-pasteurized, cooled, and pumped directly to the sterile storage tanks with the same sterility precautions as described for tomato juice. The storage tanks may be made of stainless steel or, more usually, of mild steel lined with a phenolic (epoxy) resin. Tanks holding 320,000 gal were standard in the industry for years, but modern installations usually hold 714,000 gal. Apparently grape juice can be held at 30°F for 12 months or more with little loss in quality. The large tanks are usually freestanding with refrigerated coils inside the tank, but smaller tanks could be stored in a refrigerated room. Bulk storage of juice has several important advantages: (1) The "argols," crystals of potassium bitartrate, precipitate out, which prevents the accumulation of tartrates as unsightly sediment in consumer packages; (2) a substantial amount of pooling takes place with a resulting beneficial standardization and uniformity; and (3) the juice can be withdrawn, as desired, to maintain year-round production lines. The same procedure may be used to produce and store juice concentrates. Juice can be pumped to the concentrators at 15 to 20° Brix and stored at 60° Brix. The concentrate is more stable, mi-crobiologically, because of the high sugar content. Alternatively, single strength juice can be stored for later concentration, but this is only done with white juices because two heat treatments would cause too much color degradation for colored grape juice.

Many of the fruit drinks on the market use grape juice as the main ingredient for several reasons. It is inexpensive, available in large quantities, provides sweetness, and has a desirable fruity flavor that is compatible with other added flavors. Some grape concentrates have another advantage in that they can provide a very attractive color in addition to the sugar and flavor.

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