KOSHER ? What Is Kosher ? Complete Guide to Kosher Food & Certification

WHAT IS KOSHER

Kosher Food and Jewish Dietary Law

Kosher foods are foods that comply with the Jewish dietary laws known as kashrut. These laws regulate which foods may be eaten and how they must be prepared, and they apply primarily to foods derived from living creatures.

According to kashrut, only specific species of mammals, birds, and fish are permitted for consumption. Mammals must both chew their cud and have cloven hooves, birds must belong to traditionally accepted species, and fish must have both fins and easily removable scales. Any animal that does not meet these criteria is prohibited. In addition, permitted mammals and birds must be slaughtered according to a ritual process known as shechita. The consumption of blood is strictly forbidden, and therefore meat must undergo a process of soaking and salting to remove all remaining blood before it can be eaten.

Plant-based foods—including fruits, vegetables, grains, herbs, and spices—are inherently kosher. However, certain agricultural products grown in the Land of Israel are subject to additional requirements under Jewish law, such as tithing, before they may be consumed.

Kosher dietary law also draws a strict distinction between meat and dairy products. Meat products include kosher meat (such as beef, lamb, or venison), kosher poultry (including chicken, duck, goose, and turkey), and meat derivatives such as animal-based gelatin. Dairy products include milk and all milk derivatives, such as butter and cheese. Foods processed using equipment previously used for meat or dairy products may take on that status as well.

Because of this classification, meat and dairy—or their derivatives—may not be combined in kosher food. Separate equipment must be used for the storage, preparation, and cooking of meat-based and dairy-based foods in order for them to remain kosher.

A third category of kosher food is known as pareve. Pareve foods contain neither meat nor dairy and include items such as fish, eggs from permitted birds, fruits, vegetables, grains, and other edible plants. These foods remain pareve only if they are not processed using equipment designated for meat or dairy products.

Due to the complexity of modern food production, kosher certification agencies supervise and inspect manufacturing processes to ensure compliance with Jewish law. Certified products display a symbol known as a hechsher, which assures consumers that the food has been produced in accordance with kashrut.

Jewish dietary law is primarily derived from the books of Leviticus and Deuteronomy in the Torah. Foods permitted under Jewish law are called kosher (from the Hebrew kashér, meaning “fit” or “proper”), while foods that do not meet these requirements are referred to as treif, meaning “unfit.”

Permitted and Forbidden Animals

The Torah permits only land animals that both chew their cud and have split hooves. Animals such as the pig, camel, hare, and hyrax are explicitly forbidden because they meet only one of these criteria. Only certain species of domesticated birds are permitted, while birds of prey and scavengers are prohibited.

Fish must possess both fins and removable scales to be kosher. As a result, shellfish such as shrimp, crabs, oysters, and clams are forbidden. Some marine plants may also pose kosher concerns if they are contaminated by microscopic non-kosher organisms.

Animal Products and Dairy

Products derived from non-kosher animals are prohibited, including eggs and animal by-products. Honey, however, is permitted despite being produced by bees.

Cheese and Supervision

Cheese presents particular challenges in kashrut due to the use of rennet, an enzyme traditionally derived from animal stomachs. While modern rennet is often produced synthetically or from kosher sources, Jewish law—based on rulings codified in the Shulchan Aruch—requires that cheese be produced under Jewish supervision. 

Eggs in Kosher Dietary Law

Eggs laid by kosher birds are themselves considered kosher. Despite being an animal product, eggs are classified as pareve, meaning they contain neither meat nor dairy and may be consumed with either category.

Blood Spots in Eggs

Occasionally, eggs may contain blood spots, which can affect their kosher status. Jewish law (halacha) distinguishes between eggs that may have been fertilized and those that are certainly unfertilized.

If an egg may have been fertilized, early rabbinic authorities (Rishonim) and rulings codified in the Shulchan Aruch outline a complex set of rules to determine whether the egg may be eaten. According to these rulings, if blood is found on the yolk, the entire egg is prohibited. To avoid the practical difficulty of applying these rules, Moshe Isserles records a custom of discarding any egg that contains a blood spot, regardless of its location.

Checking Eggs for Blood Spots

Regarding whether eggs must be checked for blood spots before use, the Shulchan Aruch rules that hard-boiled eggs may be eaten without inspection, since checking them is impractical. Moshe Isserles adds that while checking is not strictly required by law, there is a customary practice (minhag) to inspect eggs when they are cracked open during daylight, when blood spots would be visible.

A contemporary Ashkenazi authority notes that although halacha does not require checking eggs purchased from supermarkets, there exists a widespread custom to do so in domestic settings. In commercial food production, however, eggs are generally not checked individually, as this would be prohibitively expensive and impractical.

Gelatin in Kosher Dietary Law

Gelatin is a form of hydrolyzed collagen, the primary protein found in animal connective tissue. Because it is often derived from animal sources—such as pig skin or non-kosher cattle—it may originate from non-kosher animals, making its status under kashrut particularly complex.

Historically, gelatin has been widely used not only in food products such as jelly, trifle, marshmallows, and gummy candies, but also in non-food applications including glue, cosmetics, photographic film, medical capsules, musical instruments, and embroidery. Due to its broad range of uses and the difficulty of identifying its precise source, gelatin has long been a subject of halakhic debate.

To avoid concerns surrounding non-kosher gelatin, many manufacturers have turned to alternative gelling agents with similar functional properties. These substitutes include tapioca starch, chemically modified pectins, carrageenan, and combinations of vegetable gums such as guar gum, locust bean gum, xanthan gum, gum acacia, and agar. The growing use of these alternatives is also driven by dietary preferences, as gelatin is unsuitable for vegans and vegetarians.

In recent years, an additional solution has emerged: the production of gelatin derived from the skin of kosher fish. Fish-based gelatin circumvents many of the halakhic issues associated with animal-derived gelatin and is increasingly used in kosher-certified products, pharmaceuticals, and dietary supplements.

Ritual Slaughter and Food Preparation in Jewish Law

Ritual Slaughter (Shechita)

One of the earliest dietary prohibitions in the Torah forbids eating the flesh of animals that have been torn by beasts or that have died of natural causes. This principle, which appears in Exodus and Deuteronomy, ultimately led to the Jewish legal requirement that all meat be obtained through ritual slaughter known as Shechita.

According to Jewish law, animals must be slaughtered by a trained specialist, called a shochet, using a perfectly smooth and razor-sharp knife. The slaughter consists of a single, uninterrupted cut across the throat at a precise location, severing the carotid arteries, jugular veins, vagus nerves, trachea, and esophagus. The objective is to cause rapid loss of blood pressure and death with minimal suffering.

The knife is carefully inspected before each use; any imperfection renders the slaughter invalid, and the meat non-kosher. Rabbis traditionally require the shochet to be a knowledgeable, observant Jew of good moral standing, often trained specifically for this role.

Inspection and Glatt Meat

Jewish law further prohibits the consumption of meat from animals that were suffering from fatal disease at the time of slaughter. To comply with this rule, Orthodox practice requires a thorough post-slaughter inspection of internal organs, particularly the lungs. Traditional halacha lists approximately 70 possible defects or abnormalities.

If the lungs are found to be completely smooth and free of adhesions or scars, the meat is classified as glatt (Yiddish for “smooth”), indicating a stricter kosher standard.

A unique legal case arises when a live fetus is found inside a properly slaughtered animal. Known as a ben pekuah, the fetus assumes the kosher status of its mother and may be permitted even if issues occurred during slaughter.

Forbidden Parts of the Animal

Certain parts of a kosher-slaughtered animal remain forbidden for consumption, including specific fats (chelev), major blood vessels, tendons, and the sciatic nerve (gid hanasheh). Removing these elements—especially from the hindquarters—is complex, which is why kosher meat is often limited to cuts from the forequarters.

The Torah also mandates that specific portions of a slaughtered animal—the foreleg, cheeks, and maw—be given to a kohen (priest). While consumption before this gift is debated in rabbinic literature, normative halacha permits it, though non-kohanim may not eat these portions without permission.

The Prohibition of Blood

The consumption of blood is strictly forbidden in Jewish law, based on the principle that “the life is in the blood.” This prohibition appears repeatedly in the Torah and applies universally.

To remove residual blood, meat undergoes a preparation process called meliḥah, involving soaking, salting, and rinsing. The salt—commonly known as kosher salt—draws out blood through osmosis. Certain organs, such as the liver and heart, contain too much blood for meliḥah alone and must instead be kashered by roasting, 

Food Prepared by Non-Jews (Bishul Yisrael)

Classical rabbinic law forbids consuming foods that were prepared entirely by non-Jews, due to historical concerns about idolatry and social assimilation. This restriction, known as Bishul Yisrael, applies primarily to cooked foods, though bread from non-Jewish bakers was historically exempted.

Wine presents a special case. Non-Jewish wine (yayin nesekh) is prohibited due to its historical use in idol worship. However, cooked or pasteurized wine (yayin mevushal) is permitted, as such wine was not used for ritual offerings. As a result, kosher wine is often produced under Jewish supervision and then pasteurized, allowing it to be handled by non-Jews afterward.

Over time, rabbinic opinions have diverged. While Orthodox Judaism generally maintains stricter standards, Conservative authorities have issued rulings permitting certain foods and wines produced by automated or non-Jewish processes under specific conditions.

Meat and Dairy Separation

The Torah explicitly forbids cooking a young animal in its mother’s milk, a prohibition repeated three times. Rabbinic interpretation extends this to prohibit cooking, eating, or deriving benefit from any mixture of meat and dairy.

To prevent violations, foods are categorized as:

Fleishig (meat),

Milchig (dairy),

Pareve (neutral).

Fish, eggs, fruits, vegetables, and grains are considered pareve, while poultry and wild mammals are rabbinically classified as meat. Orthodox practice further requires separate utensils, cookware, and waiting periods between consuming meat and dairy.

FAQ: Kosher Basics

Is kosher the same as halal?

No. Kosher and halal are different religious systems with different rules, authorities, and standards—though there can be overlap in certain types of permitted foods.

Are all vegetarian foods automatically kosher?

Not necessarily. Ingredients such as cheese, emulsifiers, flavorings, and processing aids may be non-kosher. Equipment and cross-contact can also affect status.

What does “pareve” mean?

Pareve means a food contains no meat or dairy and was not heat-processed on meat or dairy equipment. Pareve foods can be eaten with either meat or dairy.

Why do kosher products cost more?

Kosher production may require specialized labor, supervision, inspections, dedicated equipment procedures, and certification oversight.

Can I rely on the ingredient list to determine if a product is kosher?

Often no. Shared equipment, unlisted processing aids, and source-dependent ingredients mean that certification is typically the most reliable indicator.

What is a hechsher?

A hechsher is a kosher certification symbol placed on products or displayed at food establishments. It indicates the item was produced under kosher supervision according to the certifying agency’s standards.

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