Science Of Pickling, Explained!

By Anusha Mishra, M. Salman Chukkan, Prof. Uday S. Annapure

The science of food preservation is as old as mankind. This technique emerged in India around four thousand years ago. The first food that is believed to have been pickled is cucumber and was consumed in the Tigris Valley of India. It was widely initiated to preserve the food materials for the people travelling for longer duration in sea voyages South Korea has ‘kimchi’ prepared from cabbage, radish and other materials. Then Germany has ‘sauerkraut’ or soured pickled cabbage. The demand for preservation increased in order to overcome improper agricultural planning, to produce value added products and to add variety in diet. Inspite of several modern food preservation techniques like chemical additives, hurdle technology, non thermal technologies, pickling of fruits and vegetables continues to have an upper edge. It is an ancestral technique. Pickles are spicy and aromatic food accessory which stimulate the sense of taste and act as appetizers. It is the process of preserving food by anaerobic fermentation in brine to produce lactic acid, or marinating and storing in the acidic solution generally acetic acid. Term pickle is derived from the Dutch word pekel, meaning brine Examples include cauliflower, carrot, radish, garlic, mango etc. It helps in the preservation of perishable foods for longer duration

Vegetables such as cucumber, cabbage, olive and onion are fermented by lactic acid bacteria which can grow in low concentrations of salt. The bacteria ferment sugars in the food to form lactic acid, which then prevents the growth of food poisoning bacteria and moulds. The amount of salt controls the type and rate of the fermentation. If 2-5% salt is used, the fermentation is carried out by bacteria that produce lactic acid. The pickle is preserved by the high level of acidity. If higher levels of salt are used (up to 16%) the product is preserved by the high salt concentration rather than by fermentation and is known as a salt-stock pickle. Fruit and vegetables can be semi-processed and stored for many months by preserving in a high salt solution. In the later season they can be processed into pickle. Sugar is added sometimes to increase the rate of fermentation. Strict attention must be paid to cleanliness and hygiene of fermented pickles as they are not heated in the process. To ensure a good fermentation and preventing the growth of undesirable bacteria, concentration of salt, pH of the mixture and temperature of fermentation must be controlled. Vegetables pickled in acetic acid (vinegar) have salt and sugar added as they are not fermented and therefore have a different texture and flavour.

Different Pickling Methods

a.   Dry salted pickles

Fruits like lemon, lime, mango, cucumber are used for the preparation of dry salt pickle. According to FPO ‘pickling in salt,’ the sodium chloride concentration should not be less than 15%. The juice is extracted due to the application of dry salt leading to the production of brine. Both microbial population and fermentation are controlled using salt that is measured using a salometer or brine hydrometer. A temperature of 21°C is ideal for lactic acid fermentation; hence the vessel is placed in a warm sunny place to allow fermentation for a week. The absence of bubble production indicates that the fermentation is complete. It takes about one to four weeks to complete fermentation to take place. The quality of fermented vegetables depends on how well the undesirable organisms are controlled during fermentation.

 

Fermentation process by Lactic acid bacteria

 

 

Different types of Pickles (Fellows 1997)

 

Product Salt Sugar Vinegar Process
Fermented Sweet

Pickle

5% then 3% 1-2% then

3%

0 then 5% Ferment for 1-2 weeks then

repacked in vinegar + salt +

sugar

Fermented sour

pickle

5% then 3% 0 then 0 0 then 5% Ferment for 1-2 weeks
Unfermented

pickle

3% 1% 5% Pack straight away and

pasteurise.

Salt-stock pickle 15% 0 0 Store  until  required.  Wash

out salt and repack as unfermented pickle

b. Pickling with vinegar

Vinegar serves as a preservative and flavouring agent to pickles. The cut vegetables are immersed in strong vinegar of about 10% strength. This prevents the dilution of vinegar by the water extracted from the vegetable and also expels the gas present in the intercellular spaces. Salt, sugar and spices are added to flavour these pickles. The vinegar concentration in the final product, in terms of acetic acid, should not be less than 2%. Vegetables pickled with vinegar gives a crunchy texture to the product. Cauliflower, onion, garlic, cucumber, celery, carrots and zucchini can be pickled using vinegar. The vegetables are blanched for about 1-2 minutes in a brine solution before transferring to the jar. The jar is cooled to room temperature and the product should be stored in a cool dry place.

c. Pickling with spices

These have a bacteriostatic effect. The essential oil of spices are more inhibitory than the corresponding ground spices. It differs with kind of spice and the micro-organisms being tested. The volatile oil of mustard are very effective against Saccharomyces cerevisiae. It seals off the air from the product. It also helps in the better adherence of seasonings to the product. For instance, during mango pickle preparation, mango are first dried to completely remove moisture. Fenugreek seeds, asafoetida, turmeric powder, tamarind, chilli powder, cloves are bacteriostatic. Extracts of the plants are inhibitory to Bacillus subtilis and E. Coli. Allicin is the active principle in onions and garlic.

d. Pickling with oil

Spice mixtures and /oil are added and the fruit or vegetable is allowed to ferment for a month. The fermentation process renders fruit soft and the fruit takes on the additional aroma and flavour of the spices. Aerobic bacteria and mould growth are prevented by covering the top with oil. Properly prepared and stored pickles can last for a year or more without spoilage. Thus, pickling of fruits and vegetables shall continue to be a promising preservation technique for the times immemorial.

 

Author

Anusha Mishra, Research Scholar, Department of Food Engineering and Technology, Institute of Chemical Technology, Mumbai

Muhammad Salman Chukkan, MTech, Final Year, Food Engineering and Technology, Institute of Chemical Technology, Mumbai

Prof. Uday S Annapure, Head, Department of Food Engineering and Technology, Institute of Chemical Technology, Mumbai

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