Advances in Cucumber Pickling

John L. Etchells, Ivan D. Jones, Thomas A. Bell.

In this country the manufacture of cucumber pickles requires annually about 240,000 tons of pickling cucumbers. The crop is the fourth largest in acreage of the national truck crops (122,000 acres). A typical annual crop is about 10 million bushels and is valued at about 16 million dollars by 50,000 growers. About one-half the acreage is centered in Michigan and Wisconsin and one-fifth in the South Atlantic States.

The industry has three major operating fields. The first is manufacture of salt stock and genuine dills from green cucumbers by natural fermentation in brine. The second is the manufacture of such staple items as sweet, sour, and mixed pickles from the brine-cured cucumbers. The third is the pasteurization of various pickle products from green cucumbers, which is essentially a canning operation.

In each field, the industry has made notable advances in the past decade. Basic studies on the fermentation of salt stock have pointed out the complex nature of the microbial, chemical, and physical changes that take place. More information on how to spice pickles has made it possible to improve the finished products. Pasteurization has resulted in increased consumption of pickle products, by reaching new consumers and by giving packers a standardized procedure for preserving and maintaining the quality of their products. Storage problems have received renewed attention, and much that is advantageous has been learned. Many of these developments are the result of cooperative research by the Department of Agriculture and the North Carolina Agricultural Experiment Station.

The use of salt for the preservation of food began early in man's efforts to store edible material for his future consumption. During the years, salt preservation, or brining, has been gradually replaced by other methods, such as canning and freezing, for the bulk of commodities required for table use between seasons of production. Brining, however, is still used to produce cucumber pickles.

In times of national emergency, as during the Second World War, salt is used to preserve other vegetables, particularly when they cannot be frozen or canned because of wartime restrictions. During the period from 1942 to 1945, our research efforts turned to brine preservation of green beans, green peas, lima beans, wax beans, corn, lettuce, carrots, tomatoes, celery, okra, and certain leafy vegetables. Recommendations were given in a bulletin for the salting and brining of such vegetables for nonpickle use on both home and commercial scale. Information gathered during the 1943 season showed that several million pounds of vegetables such as corn, green peas, green beans, celery, and okra were successfully salt-preserved by commercial concerns for use in food products. Substantial amounts were also preserved in the home by this method.

In the cucumber-pickling industry, brine salinity is usually recorded in terms of degrees salometer, as measured by a hydrometer calibrated in percentages of saturation with respect to sodium chloride (0' to 100 sal.). For the convenience of the reader, degrees salometer have been converted to the approximate equivalent in percentage of salt by weight (for example, 20 , 30 , and 40 sal. brines would approximate brines with 5, 8, and 10 percent of salt).

Cucumbers are brined in wooden vats ranging in capacity from 200 to 1,200 bushels. In the South, where fermentation is relatively rapid, the vats are filled with green cucumbers, either graded to size or mixed, and fitted with loosely constructed wooden board covers keyed down firmly with wooden 2 by 4's or 4 by 4's. Salt brine of suitable concentration is added to a level of a few inches above the cover in each vat. Next, dry salt is added on the cover of the vat to maintain the initial brine concentration, which otherwise would be diluted by the water in the cucumbers. The initial concentration ranges from 8 to 10 percent salt, depending on the individual pickling plant. Usually the brine strength is gradually raised by adding enough dry salt on the cover to give a holding strength of 16 to 18 percent at the end of 4 to 6 weeks. Under these conditions and with brine temperatures of 75 to 80 F., salt-tolerant micro-organisms grow for at least 4 months. The micro-organisms that cause the fermentation come from the cucumbers and adhering particles of soil. They use as food the soluble nutritive material, principally sugar, that diffuses into the brine from the cucumber as the result of the action of salt solution on the tissue.

The growth of the micro-organisms, or fermentation, produces lactic and acetic acids, alcohols, and gases. The type of fermentation, with respect to the microbial groups involved and the end products formed, is greatly influenced by the starting brine strength and by the rate at which it is increased. At the end of the curing process, about 3 months, the cucumbers have changed from a green, opaque, buoyant fruit to olive-colored, translucent, gas-free salt stock.

In the North, the brining procedure is different. There the intake of cucumbers is slower, and therefore the vats are not filled so rapidly as in the South. The salting method, usually a combination of brining and dry salting, consists of adding a few inches of brine as a cushion in the vat and gradually filling the vat with cucumbers and dry salt. Some of the brine is formed by action of dry salt on the cucumbers. The initial brine strength used is usually in the range of 6 to 7.5 percent and is not generally raised according to any set schedule but is dependent mostly on temperature conditions and progress of the acid fermentation. The aim is to have the stock cure out as much as possible before cold weather otherwise, vigorous gaseous fermentation takes place in the spring as the brine warms up. Another feature characteristic of northern brining stations is that most of the vats are sheltered. Shelters, which range from high sheds to enclosed buildings, prevent the dilution of the brine by rain or snow, but provide ideal conditions for the film-forming yeasts, which are absent from the brine surfaces of vats in the open and exposed to direct sunlight.

During the natural fermentation of cucumbers for salt stock, the following salt-tolerant microbial groups may be present: Acid-forming bacteria, yeasts, coliform bacteria (Aerobacter), and obligate halophilic (salt-loving) bacteria. As a result of the growth of these organisms, lactic and acetic acids, alcohol, and gases are formed.

UNDER SUITABLE CONDITIONS as to temperature and brine strength, an active acid fermentation, resulting from the growth of salt-tolerant, acid-forming bacteria, begins within a day or so after the cucumbers are brined and continues for 4 to 6 weeks. The preserving effect of the brine is due chiefly to the combined action of the salt and the developed acidity. There is a direct relationship between numbers of lactic acid bacteria and the brine strength used. For example, in 5-percent brines upward of 200 million bacteria per milliliter are found. Correspondingly smaller populations are found as salt concentrations increase. At 15 percent concentration or stronger, little or no growth by the, acid-producing bacteria is observed. The effect of salt on the growth of these organisms is shown by the degree of developed acidity. Fermentations at salt concentrations of 5, 10, and 15 percent result in decreasing brine acidity-0.7, 0.4, and 0.1 percent total acid calculated as lactic.

Identification studies on cultures of lactic acid bacteria from commercial fermentations at 5, 8, and 10.5 percent salt showed that the bacteria were Lactobacillus plantarum. Additional cultures from commercial brines at 11 to 12.5 percent salt were also identified as this species.

Yeasts associated with the cucumber brines are of two general groups: Those that produce a gaseous fermentation in the brine; and those that produce luxuriant films on the brines exposed to air but sheltered from direct sunlight. The two groups are frequently confused in the reports on cucumber pickling.

Yeasts capable of gaseous fermentation have a high tolerance to salt and acid. Fermentations are found in brines ranging from 2.5 to 20 percent salt by weight. As a rule, the salt content governs the time yeast growth starts, as well as the duration of activity. Carbon dioxide is evolved from the brine surface as long as yeasts are present. At brine temperatures of 75 to 80 F. and fermentations at 5 percent salt strength, yeast growth usually starts within 2 to 3 days and -populations drop sharply after 7 days of activity. At 10 and 15 percent brine strengths, yeasts start growing in 7 to 12 days, respectively, and the gaseous fermentation continues for a much longer period than at 5 percent. The reason for the More active development in the stronger brines is that the lactic acid bacteria are inhibited as the brine strength is increased and more fermentable material remains for the yeasts, which are not similarly inhibited.

The principal subsurface yeasts, isolated and identified during fermentation of 42 commercial vats of cucumbers at two plants, fell into the following six genera in the order of frequency of isolation: Torulopsis, 721 cultures; Brettanomyces, 588; Zygosaccharomyces, 59; Hansenula, 49; Torulaspora, 6; and Kloeckera, 1. Two new species, Torulopsis caroliniana and Brettanomyces versatilis, accounted for 88 percent of the total cultures. These results are based on fermentations under southern conditions. First results in studies on cultures obtained from northern brines indicate that yeast activity also forms part of the general fermentation of cucumbers brined in Michigan, Indiana, and Wisconsin. Several of the species Torulopsis caroliniana, Brettanomyces versatilis, Hansenula subpelliculosa, Torulaspora rosei, and Zygosaccharomyces spp. were found in both brining areas.

Film-forming yeasts do not depend on sugar for growth but use organic acids or alcohol in the brine as a source of energy. Their growth causes a decrease in brine acidity. In 1939, E. M. Mrak and Lee Bonar, of the University of California, found that the surface films on seven samples of cucumber salt stock at 18 to 20 percent salt were the result of growth by film-forming yeasts belonging to the genus Debaryomyces. However, films on seven samples of dill-pickle brines at 4 to 6 percent of salt were identified as species of the genera Mycoderma and Picha. Work by the writers shows that species of Endomycopsis, Candida, and Zygosaccharomyces, in addition to Debaryomyces, produce films on commercial cucumber brines.