Yosef Karo

“ Some people allow the meat to be salted along with fat and veins like any normal meat if it has not been left for sixty hours.
21 If a butcher is found to have cut meat with veins or forbidden fat, one instructs him to refrain from repeating that mistake. But if milk is found, the meat must be withdrawn from consumption if the milk is in a quantity equal to the size of an olive. If there is a larger quantity, the butcher must be severely punished. ”

“ It is permissible to leave the udders attached to the cow until any milk has been removed.
19 All of these laws, if they are transgressed, do not render the meat as forbidden. One should only instruct the person to avoid repeating that certain mistake. If the mistake was made, the meat is permissible, but it is recommended to wash it properly.
20 One may not salt meat before the veins and fat have been removed. If one has already salted it, it is permissible once the veins and fat have been removed. Some prohibit it, however, until the meat has been scraped clean. ”

“ If fat is found on the bottom layer or any of the tubes attached to it, it is also forbidden. One must remove that fat as well.
Note: It is important to know that the milk found on the gallbladder should not be consumed, even if it is found only on the surrounding fat, because it is dangerous to human health.
13 The veins (or nerves) which are entangled in an animal’s gut on the top right side of the animal’s stomach and have five strands, of which three branch off to the right side while two branch off to the left, are prohibited. ”