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. Rabbi Hershel Schachter argued that with modern dairy-farm equipment, milk from the minority of non-kosher cows is invariably mixed with that of the majority of kosher cows, thus invalidating the permissibility of consuming milk from a large dairy operation. Many leading rabbis, however, rule milk permissible, as do major kashrut authorities. Human breast milk Breast milk from a woman is permitted. However, 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. Cheese The situation of cheese is complicated as hard cheese often involves rennet, an enzyme that splits milk into curds and whey. Many forms of rennet are derived from the stomach linings of animals, but since the 1990s rennet is often made recombinantly in microbes because it can be produced more efficiently (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