Fermentation Sorting and size grading (air exposure)

Slow loss of sugars, tannins, and oleuropein.

Formation of organic acids, ethanol, acetaldehyde, and ethyl acetate.

Final phase

Storage in brine Canning

Packing and storage

None, under normal conditions and it is regulated in such a way that the treatment takes a determined number of hours to reach the suitable penetration for each variety. As a general rule, time for the majority of the varieties is 5 to 7 h, except for Gordal and Ascolano, which require a slower treatment, around 9 to

10 h, with more diluted lyes because of the texture and composition of the skin and flesh. A good control of the factors mentioned previously (lye concentration, lye penetration, and time of the treatment) is essential for the quality of the final product. When the fruits are treated with too much of a low-concentration lye and hence over a longer time, the further developed color may be only fairly acceptable and the fermentation will be poor. Conversely, a high-lye concentration may produce texture deficiencies and a high loss of fermentable matter, which is important to further fermentation.

After the alkaline treatment, the fruits are washed with water to eliminate the major portion of the lye that remains in the flesh. The duration and number of necessary washings are also important factors. An excessive number of washings can deplete the fermentable matter and nutrients in such a way that it will be necessary to add more of those compounds to complete the fermentation process. An excessive amount of organic salts may also be lost, producing as a consequence a lack of buffer capacity of the medium. Finally, a long period of washing may lead to serious bacterial contamination before the fruits are placed into the brine. On the contrary, excessively short washings produce a high concentration of organic salts (frequently called residual lye) in the fruits, which further prevents the attainment of suitable pH values during fermentation (81).

In summary, for each variety, stage of maturity, and temperature, a compromise must be found between lye treatment and the washing system that permits the fruits, when placed in brine, to retain enough fermentable compounds to reach a suitable degree of free acidity during fermentation and a concentration of organic salts (normally around 0.1 N) that will maintain the right pH value for safe storage of the fruits in brine. If the lye treatment is correct, a quick rinse after the alkaline treatment, followed by a first washing of 2 to 3 h and a second washing of 10 to 12 h, is the schedule normally used in the factories.

After washing, fruits are placed into a brine of sodium chloride in which lactic acid fermentation takes place. The brine, by osmosis of the components of the fruit, is transformed in a rich culture medium for microorganisms that are responsible for fermentation. The speed of that transformation depends on the variety, lye treatment and washings, ratio of fruit to brine, salt concentration, temperature, and so on. The order of appearance of growth of different microorganisms is dependent on their nutritive requirements.

The concentration of initial brine is quite important. If too low, the also low osmotic pressure can lead to spoilage by sporulating microorganisms of the Clostridium type during the first stage of fermentation, if the pH value remains too high. On the contrary, if the concentration of salt is too high, fruits may become irreversibly wrinkled (86). Depending on the variety and the stage of maturity of the fruit, initial concentration must be regulated between 9 and 11 Beaume degree units.

After the initial decrease in the salt concentration, it must be gradually increased to maintain a good texture in the fruit and allow good fermentation and storage (86). However, the increments of salt must be slow enough to permit the right growth of the lactic acid bacteria.

A good approach is to maintain the salt concentration between 5 and 6% during the greater part of the fermentation phase, rising to 7% at the end of that part of the process. Furthermore, it may be increased up to 8% or even more during the storage phase to avoid the growth of Pro-pionibacteria during the last stage of fermentation, which may produce a depletion of lactic acid.

At present, the containers used for all the fundamental phases of the process (treatment with lye, washing, fermentation, and further storage of the fermented product) in the majority of the producer countries are fermentors made of polyester and fiberglass. They can be fully closed to create anaerobic conditions and exclude the growth of yeast films on the surface of the brine. The containers have a large opening on the top and valves at the top and the bottom that facilitate the unloading of the fruits and the circulation of the brine. The most common capacity for these is about 10 t of fruit, some even 15 t. The same material is used for underground fermentors. In those cases, the opening at the top is used for all operations—loading, unloading, and recirculation of the brine—by use of suitable pumps.

The four phases of spontaneous fermentation of pickled green olives in brine have been described in detail. Each of them is characterized by a different development of the microbial population as well as by changes in the physical chemical characteristics of the culture medium, which is constituted by the initial brine and the soluble compounds of the fruit that pass to it by osmosis.

The duration of each phase as well as the relative importance of the growth of certain microorganisms depend on a series of factors, among which the following must be emphasized.

• Prior treatments of the olives (lye treatment, washing operations, and initial concentration of the brine)

• Capacity of the fermentor and, as a consequence, the ratio of fruit weight to brine volume

• Climatic and environmental conditions in the factory

• Variety of the olives

• Sanitary conditions of the plant and equipment

In all cases, the natural sequence of appearance, growth, and disappearance of microorganisms may be established as follows:

• Gram-negative bacteria, the majority of which belong to the Enterobacteriaceae family. They are the first to appear and grow, at the relatively high pH values of the initial brine.

• Lactic-acid-producing cocci, mainly from the genus Pediococcus (homofermentative) and Leuconostoe (heterofermentative). Their major or minor growth may have, together with other factors and the action of gram-negative bacteria, an influence on Lactobacilli, mainly from the species L. plantarunz, which, under normal conditions, become predominant in the third phase and are responsible for the typical fermentation of Spanish-style pickled green olives in brine.

• Propionibacterium genus, which, as indicated earlier, may grow during the fourth phase with depletion of lactic acid if salt concentration in the brine is not suit ably controlled during the storage of the fermented fruits.

A variable and nonabundant fermentative yeast population coexists with Lactobacilli throughout the whole fermentation period and probably partially contributes to the sensory properties of the final product. However, film-forming oxidative yeasts must necessarily be avoided with a suitable anaerobic closing of the fermentors. Each genus and species gradually adapts the characteristics of the medium to the requirements of the microorganism that succeeds it within the natural sequence, until the last one becomes dominant.

The correct control of a reduced number of factors, such as pH value, free and combined acidity, salt concentration, temperature, degree of aerobiosis or anaerobiosis, and use of a pure culture as starter, permits food technologists to vary the duration and relative importance of each of the phases and avoid the microorganisms that can have negative effects on the quality of the final product.

Acidification or injection of C02 into the brine during the first stage to prevent the development of gramnegative bacteria, and a further inoculation with a pure culture of L. plantarum or a well-fermented brine with a good population of active Lactobacilli, is a very efficient method to reduce to a minimum the effect of the first and second phases and accelerate the start of the fundamental third phase. A well-controlled fermentation process produces a final product that, in general, shows pH values of 3.8 to 4.2 units and a free acidity between 0.8 and 1.2%, expressed as lactic acid and mainly composed of that acid. The figures for combined acidity, also improperly called residual lye, oscillate between 0.09 N and 0.11 N, approximately. The final salt concentration should be about 7%, if the storage period is expected to be relatively short and room temperature is not too high. However, for longer periods of preservation or high summer temperatures, it is better to raise the sodium chloride concentration to at least 8%, to avoid the growth of Propionibacterium species. Only Lactobacilli in their declining phase and some fermentative yeasts constitute the microbial population of the fermented product.

Green olives to be sold are bottled or canned in small, hermetically sealed containers, which generally present the characteristics summarized in Table 10. The right selection of those parameters, the most important of which are fixed by the international standard of the IOOC, permits the bottled or canned product to be kept safely without pasteurization, and no sediment is formed in the container (87). According to those standards, salt concen-

Table 10. Topical Ranges for the Main Physical Chemical Parameters of Pickled Olives in Brine


Spanish-style green olives

Californian-style black olives

Greek-style black olives

pH value

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