2mm thin sliced Beef Chuck cut from USDA choice or higher beef. It is used for hot pot.

Beef not exposed to oxygen (in vacuum packaging, for example) is burgundy or purplish in color. After exposure to the air for 15 minutes or so, the myoglobin receives oxygen and the meat turns bright, cherry red. After beef has been refrigerated for about five days, it may turn brown. This darkening is due to oxidation, the chemical changes in myoglobin due to the oxygen content. This is a normal change during refrigerator storage. Beef that has turned brown during extended storage may be spoiled, have an off-odor, and be tacky to the touch and should not be used.