The Babylonian Talmud cites an early example of a kashrut seal: the seal of the Kohen Gadol on jugs containing olive oil used in the Jewish Temple for the lighting of the Menorah. 'LMLK seals' (bearing the Hebrew letters , equivalent to LMLK) were stamped on the handles of large storage jars mostly in and around
Jerusalem during the reign of King
Hezekiah (circa 700 BC), based on several complete jars found
in situ buried under a
destruction layer caused by
Sennacherib at
Lachish. None of the original
seals have been found, but about 2,000 impressions (also referred to as
stamps) made by at least 21 seal types have been published. An 11th-century certificate found in the
Cairo Geniza written by a rabbinical court, testified the kosher status "according to rabbinic law" of the cheeses being sold by a
Karaite grocer, Yefet b. Meshullam of Jerusalem. The document explains that the cheese was produced in a factory on the
Mount of Olives that followed rabbinic practice. The certificate reads: "The cheeses are kosher and it is appropriate for Rabbanite Jews to purchase them. We grant this permission only after having made a formal purchase from him and having witnessed an oath he took on the holy Torah." The practice of marking food as a sign of kashrut can be dated back as far as the 6th century CE. A clay stamp bearing a Menorah image from this period was discovered in an excavation near
Acre, Israel in 2011. According to archeologists, local Jews stamped their dough with Menorah impressions while preparing bread, in order for consumers to verify its kashrut. In New York City in the late 18th and early 19th centuries a
shochet (kosher slaughterer) sold meat from the animals he slaughtered, with a seal affixed certifying it was kosher, to butchers who also sold non-kosher meat. In 1796 the city's
Common Council suspended the butcher license of a non-Jewish butcher, Nicholas Smart, for seven weeks for selling non-kosher meat with a counterfeit seal. In 1805 another non-Jewish butcher, Caleb Vandenburg, also had his butcher license temporarily suspended after Jacob Abrahams, who had been the shochet in New York since 1803, inspected meat to which Vandenburg had affixed a seal saying it was kosher and testified that he had not slaughtered the animal the meat came from. The proliferation of factory-produced foods following World War II saw a concomitant rise in kosher certification. In 1950, for example, the OU's staff of around 40
mashgichim (rabbinic field representatives) certified 184 products for 37 companies; by 1972, the OU had more than 750
mashgichim certifying over 2,500 products for 475 companies. In the late 20th century, the increasing use of pre-processed ingredients – such as
artificial flavorings,
emulsifiers, and
preservatives – further broadened the scope of kosher certification. A product produced in one country can contain ingredients and flavorings produced in other countries; these ingredients and flavorings must be tracked to their point of origin to verify their compliance with
kashrut laws. According to a 2013 estimate, the 135,000 food products then certified kosher contained more than one million food additives. Certification agencies regularly send
mashgichim to factories in
China,
Thailand, and the
Philippines to oversee the production of pre-processed ingredients and ensure their kosher status. ==What requires kosher certification==