A pickle is a food preserved either by fermentation in brine, preservation in vinegar or another acid, or a combination of the two. The acid environment produced by the pickling process may render the food safe and stable without sterilization, or it may be appropriate to can at boiling-water temperatures; the steam pressure of an pressure cooker is rarely needed.
Some preservation techniques not using heat still require heat. The containers used for pickling must be clean. Certain fermented foods, such as sauerkraut or kimchi, must keep the solid food (e.g., a cabbage mixture) submerged under the pickling liquid; mold may form on parts exposed to air.
Types of pickles
Five main types are recognized in Western cooking,  although there are variants in other cultures:
- Brined pickles: most commonly based on cucumbers or cabbage and spices, these are fermented in brine for several weeks. Some especially acid products, such as Moroccan preserved lemons, cure more quickly than the 6-8 weeks typical of more neutral produce.
- Fresh pack pickles: A much quicker process, which may involve brine pickling taking hours, but the main preservation is in vinegar.
- Relishes: Relishes involve an initial cooking step, for forming flavors and texture rather than preservation. They are more likely to need hot water canning
- Fruit pickles: Rather than vinegar or brine, these usually cooked products use a concentrated sugar solution, which both sweetens but also inhibits microbial growth.
- Chutneys and sauces: These have some similarities to fruit pickles, but are longer-cooked, so that the fruits or vegetables break down into a soft texture. They may use a substantial amount of vinegar as well as sugar. The line between chutneys and hot-water-preserved acid fruit jams and jellies can be a thin one.
- Ball Corporation (1997), Ball Blue Book: Guide to Home Canning, Freezing & Dehydration, Alltrista Corporation, pp. 42-43
- Chutneys and sauces