Overview
There are 258 frozen fruit, juice and vegetable plants in the United States, with the highest concentration in California, Washington and Florida. They tend to be concentrated near to the growing areas where crops are produced. These plants are characterized by the use of large quantities of hot water and steam, and of refrigeration, making them good candidate sites for on-site power production (CHP, Cogen).
Major Processes
Fruit and vegetables are processed and preserved in a large range of products. Fruits and vegetables are harvested at times when they are at peak quality, and sent to the plant for processing. Although there are many similarities between the processing of fruit and vegetables, it is important to realize the following differences.
Fruits are nearly all acidic and are commonly called ‘high acid’ foods. This acidity naturally controls the type of micro-organisms that are able to grow in fruit products. The spoilage microorganisms that are likely to be found in such products are moulds and yeasts, which if consumed, rarely cause illness. Processing may be achieved by using preservatives such as sugar, salt and vinegar, and by drying, concentration or fermentation.
Vegetables are less acidic than fruits and for that reason are classified as ‘low acid’ products. A wide range of micro-organisms are able to grow in moist low-acid products, which may lead to spoilage and the possibility of food poisoning. To prevent this, vegetables can be processed by heating to destroy bacteria, or by pickling, salting, or drying to inhibit bacterial growth. Care is needed when processing low acid products, such as vegetables, to minimize the risk of transmitting food poisoning bacteria to consumers.
Produce is cleaned, sorted and peeled as required. If skin is to be removed, items may be softened. Caustic wash tanks that are usually steam heated. Further mechanical processing includes husking, slicing, cutting, crushing and mixing. These processes may use high horsepower electric motors, which may result in large demand loads for electrical power.
Fruits and vegetables must be stabilized to prevent natural enzymes causing changes of color and taste during frozen storage. Some produce Is blanched In steam-heated vessels. Blanching consumes large amounts of steam. Vegetables must be blanched before freezing to prevent the development of off-flavors and colors during frozen storage. Fruit is rarely blanched because this can cause the fruit to become soggy upon thawing, instead chemicals are used without heat to inactivate the enzymes.
Fruits and vegetables are frozen in individual quick freeze (IQF) units or blast freezers. Process and storage refrigeration is the largest consumer of electricity in these plants; it averages about 70% of electricity consumption in the plants producing frozen fruits and vegetables.
Major Equipment
Natural Gas Technologies