A jar of Indian pickle sits on a shelf for months in a hot climate and stays sound. Three mechanisms are working together, and each of them is doing something a modern refrigerator does differently.
Salt removes the water microbes need
Microbial growth depends not on how much water is present but on how much of it is free and available.
Heavy salting draws water out of the vegetable and binds what remains, so the liquid in the jar becomes a concentrated brine that most spoilage organisms cannot grow in.
This is why the first stage of most Indian pickles is salting and resting the cut vegetable, and why the liquid that appears is retained rather than discarded.
Oil seals the surface from air
A layer of oil covering the contents blocks contact with oxygen, which most moulds and many spoilage bacteria require.
Mustard and sesame oils are traditional partly because they carry their own antimicrobial compounds alongside their flavour.
The instruction to keep the pickle submerged and to use a dry spoon is not fussiness. A piece protruding above the oil is the point where spoilage reliably starts.
Acid and spices narrow the field further
Lemon, lime, vinegar or the natural acidity of unripe fruit lowers the pH into a range where many organisms cannot establish.
Several of the spices used in quantity, including mustard, fenugreek, turmeric and chilli, carry compounds that inhibit microbial growth in their own right.
None of these alone would be sufficient in a warm climate, but combined with salt and oil the margins become wide.
Sun-drying is part of the process, not a preliminary
Many recipes call for the salted vegetable to be dried in the sun for days before oil and spices are added.
That step removes a further large share of the water, concentrating flavour and pushing the water content below what most organisms tolerate.
It is also why traditional pickle-making is seasonal, tied to a period of dry heat rather than to when the vegetable is cheapest.
Refrigeration changes what a pickle is
Chilled pickles can use far less salt, less oil and less acid, because low temperature does much of the preserving.
The result is fresher tasting and closer to the raw vegetable, and it also has a shelf life measured in weeks rather than seasons.
The two are genuinely different products, which is why a traditional recipe tastes over-salted when treated as a fresh condiment and a fresh one spoils when treated as a preserve.