Anyone that has savored a USDA Prime Graded Steak knows that it is delightfully tender and juicy with a buttery flavor which makes it distinctively superior to any other steak. Of all the beef produced in the US, less than 2% is certified as USDA Prime. Typically you will not find USDA Prime in the supermarkets since its limited supply is gobbled up by fine meat purveyors that retail it to upscale restaurants and affluent consumers.
The United States Department of Agriculture (USDA) meticulously grades beef at the request of a meat packer. Only beef that is USDA inspected may carry the USDA shield of authenticity. The grading system determines the quality rating of beef based upon a very complicated inspection system which measures the amount of marbling (fat specs) in the ribeye muscle (lean) portion and combines the maturity (age) of the beef carcass to determine the inspected grade.
The higher the ratio of marbling and the younger the beef, the higher the grade. It is the fat marbling which determines tenderness, juiciness and flavor. The age of the beef determines beef texture and also effects flavor. Younger beef produces a finer texture and a lighter red color.
Therefore USDA Prime Grade has the highest rating of a combined high ratio of marbling with the youngest maturity of beef. That's why prime is the most flavorful and most tender with the finest of texture.
Although there are eight levels of USGA graded beef there are generally only three USDA grades of beef that you would buy in a supermarket, a butcher shop or a restaurant. They are USDA Prime, Choice or Select which is the order of grade from the highest to lowest.
Two lesser grades are Cutter and Canner which is what you would typically find in frozen pot pie dinners, microwave burritos, hamburgers and other processed food products. USDA Select is not very far above the bottom of the edible barrel, though some major chain stores will try and infer to a consumer that Select is a premium grade that is often marketed with a "catchy brand".
Beware of marketing deceptions. Some supermarkets may try to fool an unsuspecting consumer by using the words "prime" and "choice" without being attached with the official "USDA shield". Unless prime and choice carries the USDA label, what you are buying may not be the real thing.
Some upscale restaurants employ clever wordsmiths to write menu copy that deceives you into thinking you are ordering a USDA Prime Steak when in reality you may be being served the less costly "Choice" version. In fairness to restaurants that serve USDA Choice Filets, it's degree of marbling could closely approach that of Prime when the measurement is very near the threshold that separates it from Prime.
When shopping for quality steaks, always look for the USDA shield. When ordering a steak always ask your server what the USDA grade actually is. Often you'll hear a bit of stuttering and a quick diversion from the subject. That's a signal to become more inquisitive.
USDA Prime is the superior grade with amazing tenderness, juiciness, flavor and fine texture. It has the highest degree of fat marbling and is derived from the younger beef. That's why Prime is generally featured at the most exclusive upscale steakhouse restaurants.
USDA Choice is the second highest graded beef. It has less fat marbling than Prime. Choice is a quality steak particularly if it is a cut that is derived from the loin and rib areas of the beef such as a tenderloin filet or rib steak. Generally USDA Choice will be less tender, juicy and flavorful with a slightly more coarse texture versus Prime.
USDA Select is generally the lowest grade of steak you will find at a supermarket or restaurant. You will find it tougher, less juicy and less flavorful since it is leaner than Prime and Choice with very little marbling. The texture of Select is generally more coarse. Therefore, Select is not nearly as enjoyable or desirable.
The above description of how beef is graded by the USDA is basic overview. For more detail of exactly how a beef certifier measures marbling, maturity of the beef, the color of beef and its texture to determine an accurate USDA Grade, read the United States Standards for Grades of Carcass Beef established by the US Department of Agriculture.