In addition to meat,
products of forbidden species and from unhealthy animals were banned by the Talmudic writers. This included eggs (including fish
roe), as well as derived products such as jelly, but did not include materials merely "manufactured" or "gathered" by animals, such as
honey (although, in the case of honey from animals other than bees, there was a difference of opinion among the ancient writers). According to the rabbinical writers, eggs from ritually pure animals would always be
prolate ("pointy") at one end and
oblate ("rounded") at the other, helping to reduce uncertainty about whether consumption was permitted or not.
Dairy products The classic rabbinical writers imply that milk from an animal whose meat is kosher is also kosher. As animals are considered non-kosher if they are discovered to have been diseased after being slaughtered, this could make their milk retroactively non-kosher. By adhering to the principle that the majority case overrules the exception, Jewish tradition continues to regard such milk as kosher, since statistically it is true that most animals producing such milk are kosher; the same principle is not applied to the possibility of consuming meat from an animal that has not been checked for disease. Many leading rabbis rule milk permissible, as do major
kashrut authorities. Authorities assert breast milk may be consumed directly from the breasts only by children younger than four (five if the child is ill), and children older than two were only permitted to continue to suckle if they had not
stopped doing so for more than three consecutive days. (though many artisanal cheeses and cheeses made in Europe still use animal rennet). Because the rennet could be derived from animals, it could potentially be non-kosher. Rennet made recombinantly, or from the stomachs of kosher animals, if they have been slaughtered according to the laws of
kashrut, can be kosher. Cheese made from plant-derived rennet can also be kosher. Many authorities require that the cheese-making process follow certain stringencies to be kosher. According to the
Shulchan Aruch, a rabbinic decree (called
gevinat akum) prohibits all cheese made by non-Jews without Jewish supervision, even if its ingredients are all kosher, because very frequently the rennet in cheese is not kosher.
Rabbeinu Tam and some of the
geonim suggested that this decree does not apply in a location where cheese is commonly made with only kosher ingredients, a position that was practiced in communities in
Narbonne and Italy. Many contemporary
Orthodox authorities do not follow this ruling, and hold that cheese requires formal
kashrut certification to be kosher; some even argue this is necessary for cheese made with non-animal rennet. However, some such as
Joseph B. Soloveitchik ate generic cheeses without certification.
Isaac Klein's
tshuva authorized the use of cheese made from non-kosher rennet, and this is widely practised by observant Conservative Jews and Conservative institutions.
Eggs made with egg noodle, caramelized sugar and black pepper The
eggs of kosher birds are kosher. Eggs are considered
pareve despite being an animal product.
Blood found in eggs Occasionally blood spots are found within an egg, which can affect the kosher status of the egg. The
halacha varies depending on whether or not there is a possibility of the egg being fertilized. If the egg may have been fertilized, the
Rishonim and Shulchan Aruch suggest a complex set of rules for determining whether the egg may be eaten; To avoid the complexity of these rules,
Moshe Isserles records a custom not to eat any such eggs with blood spots. This is the case nowadays, when
battery eggs form the majority of available produce. Regarding the question of whether one must check an egg for blood spots, the Shulchan Aruch rules that one may eat hard-boiled eggs where checking is impossible. Moshe Isserles adds that checking is not required, but that a custom exists to check eggs if they are cracked during the daytime (when blood could be seen). the main protein in animal
connective tissue, and therefore could potentially come from a non-kosher source, such as pig skin. Gelatin has historically been a prominent source of glue, finding uses from musical instruments to
embroidery, one of the main historic
emulsions used in
cosmetics and in
photographic film, the main coating given to
medical capsule pills, and a form of food including jelly,
trifle, and marshmallows; the status of gelatin in
kashrut is consequently fairly controversial. Due to the ambiguity over the source of individual items derived from gelatin, many Orthodox rabbis regard it as generally being non-kosher. However, Conservative rabbis and several prominent Orthodox rabbis—including
Chaim Ozer Grodzinski and Ovadia Yosef—argue that gelatin has undergone such total chemical change and processing that it should not count as meat, and therefore would be kosher. Technically, gelatin is produced by separating the three strands in each collagen fiber's triple helix by boiling collagen in water. David Sheinkopf, author of
Gelatin in Jewish Law (Bloch 1982) and
Issues in Jewish Dietary Laws (Ktav 1998), has published in-depth studies of the kosher uses of gelatin, as well as
carmine and
kitniyot. One of the main methods of avoiding non-kosher gelatin is to substitute gelatin-like materials in its place; substances with a similar chemical behaviour include
food starch from
tapioca, chemically modified
pectins, and
carrageenan combined with certain vegetable gums—
guar gum,
locust bean gum,
xanthan gum,
gum acacia,
agar, and others. Although gelatin is used for several purposes by a wide variety of manufacturers, it has started to be replaced with these substitutes in a number of products, due to the use of gelatin also being a significant concern to
vegans and
vegetarians. Today manufacturers are producing gelatin from the skins of kosher fish, circumventing many of these problems. ==Ritual slaughter==