Preservation by salt and pickling
Salt draws water out of microbes and lowers water activity. Indian pickles combine salt, acid, oil and spices to keep raw mango, lime and vegetables for months.
How salt preserves
Salt dissolves in the food's water and raises osmotic pressure, drawing water out of microbial cells (plasmolysis) and lowering water activity. Chloride ions are also toxic to some microbes, salt lowers the oxygen dissolved in brine, and it slows protein-splitting enzymes. High salt (about 15-20%) stops most spoilage organisms. Low salt (a few per cent) only holds spoilage organisms back while lactic acid bacteria turn sugars into acid, as in sauerkraut (about 2.5% salt) and brined lime or mango. Salt-loving (halophilic) bacteria can still turn salted fish pink. Methods: dry salting (salt rubbed or layered: fish, raw mango, lime) and brining (food immersed in salt solution: vegetables, cheese).
Types of pickles
| Type | Preserving agents | Indian examples |
|---|---|---|
| Salt (brine) pickles | Salt, often with lactic fermentation | Salted lime, brined raw mango kept for later use, salted green chillies |
| Oil pickles | Salt and spices under a covering layer of oil | Mango avakkai, cut-mango pickle, lime, garlic, gongura |
| Vinegar pickles | Acetic acid (vinegar), salt and spices; usually not fermented | Onion, carrot, green chilli and mixed vegetable pickles |
| Sweet pickles and chutneys | Sugar with vinegar and spices | Sweet mango chutney, sweet lime pickle, tomato chutney |
Practical: cut-mango oil pickle
- 1Select raw, firm, sour mangoes with no bruisessoft or ripe fruit spoils
- 2★Wash and wipe completely dryany water left invites mould and yeast
- 3Cut into pieces, with or without the seed shelldry knife and board
- 4Mix with salt, turmeric, chilli powder, mustard powder and roasted fenugreek powderspices add flavour and some antimicrobial action
- 5Heat gingelly (sesame) oil with asafoetida and let it coolremoves moisture and raw smell
- 6★Pack into clean, dry glass or ceramic jars (bharani) and pour oil to cover the piecesthe oil layer shuts out air
- 7Cover with a clean cloth for 2-3 days, mixing daily with a dry spoon; then close and labelmatures in a week or two
★ one-way, controls the pace
Worked example: making brine and reading its strength
Prepare 2 kg of 10% brine (by weight) for brining green chillies. What is its salometer reading?
- 10% brine by weight = 10 g of salt in every 100 g of brine.
- Salt = 2000 × 10 ÷ 100 = 200 g; water = 2000 − 200 = 1800 g (1.8 litres).
- Saturated brine holds about 26.4% salt and reads 100° on the salometer.
- Salometer reading = 10 ÷ 26.4 × 100 = 37.9°, about 38°.
- Careful: '100 g of salt in 1 litre of water' is not 10%; it is 100 ÷ 1100 × 100 = 9.1% by weight.
Dissolve 200 g of salt in 1.8 litres of water; the brine reads about 38° on the salometer.
Spoilage of pickles
| Defect | Cause | Prevention |
|---|---|---|
| White scum or film on top | Film yeasts growing at the surface and using up the acid | Keep pieces under brine or oil; cover; use a dry spoon |
| Softening and slipperiness | Pectin-splitting moulds and bacteria; too little salt or acid | Correct salt; remove scum; firm raw fruit |
| Darkening or blackening | Iron from vessels or water; some bacteria; exposure to air | Glass or ceramic jars; keep pieces covered |
| Mould growth | Moisture in jars, spoons or fruit; too little salt or oil | Dry jars, dry spoons; enough salt and oil |
| Shrivelling | Very strong salt, sugar or vinegar added all at once | Raise the strength gradually |
| Hollow or bloated pieces | Gas from yeasts or coliforms inside the pieces | Correct brine strength; firm produce |
Pickles add flavour and appetite but are very high in salt (sodium) and often in oil; even a small spoonful adds a lot of sodium. Hypertensive, heart and kidney patients should avoid or strictly limit them, and hospital menus should leave pickles out of low-sodium therapeutic diets.
2 marks: “How does salt preserve food?” Salt raises osmotic pressure, draws water out of microbial cells (plasmolysis) and lowers water activity; chloride ions and less dissolved oxygen also hold microbes back.
5 marks: “Write a note on the spoilage of pickles.” White scum, softening, darkening, mould, shrivelling, hollow pieces: causes (film yeasts, pectin-splitting microbes, iron, moisture, wrong strength) and prevention.
10 marks: “What are pickles? Classify them and describe the preparation of mango pickle.” Definition; types (salt, oil, vinegar, sweet); roles of salt, oil, acid and spices; steps for mango pickle; spoilage and prevention.
A pickle's enemies are water and air: dry fruit, dry jar, dry spoon, oil on top.