The yellow stuff in ground beef is fat that has a yellow color due to the presence of beta carotene that comes from the grass that the cow ate.
The yellow stuff in the ground beef is a natural occurrence in grass fed beef and indicates that the cow was primarily fed on pasture grasses.
The beta carotene is a pigment that is found in grass and when the cow eats the grass it gets stored in the cow's fat and gives it the yellow hue.
seeing the yellow color in the ground beef is a good sign meaning that the cow ate a healthy grass fed diet.
The filler in ground beef is known as pink slime and is a cheap filler added to around 70 percent of ground beef that is sold at supermarkets and up to 25 percent of each American hamburger patties.
Most ground beef is made from the less tender and less popular cuts of beef.
Trimmings from more tender cuts may also be used.
Grinding tenderizes the meat and the fat reduces its dryness and improves flavor.