Food is considered kosher when both its ingredients and its entire production process follow Jewish dietary law, called kashrut. This covers what the food is, how it’s prepared, and how it’s served and mixed with other foods.

Core idea: what “kosher” means

  • Kosher means food that complies with Jewish dietary laws found in the Torah and later rabbinic tradition.
  • These laws define which animals are permitted, how they must be slaughtered, which mixtures are forbidden, and what kind of supervision is needed.
  • Many simple, unprocessed plant foods are naturally kosher as long as nothing non‑kosher is mixed in and they are free of insects.

1. Allowed vs. not allowed animals

  • Land animals must both chew their cud and have split hooves (for example cows, sheep, goats); animals like pigs or rabbits are not kosher.
  • Kosher fish must have fins and visible scales; shellfish such as shrimp, crab, and lobster are not kosher.
  • Only certain traditional bird species are accepted as kosher (such as chicken, turkey, duck, goose), while birds of prey are not.

2. Slaughter and preparation of meat

  • Even a permitted animal is only kosher if it is slaughtered by a trained specialist (shochet) using the shechita method, designed to be quick and minimize suffering.
  • The meat must be inspected for certain defects and all blood is removed by soaking and salting, since consuming blood is forbidden.
  • Certain fats and specific parts (like the sciatic nerve) are not eaten and must be removed for the meat to remain kosher.

3. Meat, dairy, and pareve separation

  • Kosher food is grouped into three categories: meat, dairy, and pareve (neutral, like eggs, fish, fruit, vegetables, and grains).
  • Meat and dairy cannot be cooked or eaten together, and observant households usually keep separate dishes, utensils, and cookware for each.
  • Pareve foods can be eaten with either meat or dairy as long as they were not processed on non‑kosher or cross‑contaminated equipment.

4. Processing, ingredients, and supervision

  • Processed foods are only kosher if every ingredient (including things like gelatin, emulsifiers, flavorings) is kosher and produced on kosher‑certified equipment.
  • Wine and grape products have extra rules: they usually require specific Jewish handling and certification to be kosher.
  • Many kosher products carry a certification symbol (a “hechsher”) from a rabbinic authority showing the factory, ingredients, and processes are regularly supervised.

5. Plant foods, bugs, and the “details”

  • Fruits, vegetables, grains, and legumes are inherently kosher, but they must not contain insects, which are not allowed.
  • Some communities use very careful washing and checking methods, especially for leafy greens and berries, to avoid even tiny insects.
  • Bread, oils, and other simple foods can lose kosher status if they contact non‑kosher fats, meat, or dairy during processing.

6. In practice: when is a food kosher?

A specific food is kosher only if all of these are true:

  1. Its basic ingredients are permitted by kashrut (no forbidden animals or mixtures).
  1. Any meat in it comes from kosher species slaughtered and processed according to Jewish law.
  1. It respects separation of meat and dairy in both recipe and production equipment.
  1. It is free of insects and other non‑kosher contaminants.
  1. For processed foods, a reliable kosher certification confirms the above steps.

TL;DR: What makes a food kosher is not just what it is, but how every step—from farm to factory to kitchen—follows Jewish dietary law.

Information gathered from public forums or data available on the internet and portrayed here.