Those little white specs of fat throughout the red meat; the ones that can make a steak appear pink in the really expensive, high grade Wagyu - thats marbling.
Marbling is the tenderising and flavour enriching fat interspersed throughout the meat, not the big chunks, the chewy lines or the fat on top. It's the good stuff. It's the right kind of fat and it has a big impact on the quality of the beef - its texture, its flavour and how it will cook. Understanding marble score and its relationship to different cuts, different breeds and varying farming techniques makes choosing that perfect cut much easier and far more reliable.
The AUS-MEAT grading system determines and awards a marble score. An independent, qualified assessor inspects the eye of ribeye; a cut of steak taken from within the scotch fillet, and awards a marble score from 0 (no marbling) to 9+ (extensive marbling). Understanding that this score is determined from inspecting just one cut is important as each muscle develops unique and varied marbling and the scores should be interpreted accordingly. The rump for example only develops light marbling compared to a sirloin and, even if taken from beef that receives a high marble score, its marbling may be somewhat mild.
So what does marbling mean for different cuts and different cooking methods? In general, slow cooked meats will be juicier and easier to achieve that 'melt in mouth' or 'fall off the bone' texture without risk of overcooking and drying out. Steaks will be richer, softer and easier to develop that delicious caramelised outer umami layer, but beware - the game changes completely with high marbling!
As a general guide and referring to steaks cut from the ribeye, sirloin, tenderloin and their variations; the steaks will continue to simply get softer and more flavoursome up to a marble score of 6. They will cook beautifully as you would normally cook a steak but be richer, tastier and softer. More marbling to this point is just better. Beyond marble score 6, the fat begins to change everything; the meat gets super rich and the texture becomes a soft, buttery melt in your mouth experience like no other. But be careful, at these high marble scores the steak will need to be cooked very carefully to caramelise the outer layer and soften the marbling without overcooking and melting it away into nothing. Keep in mind, high grade Wagyu should be eaten in smaller quantities. At MB9+ expect to be satisfied after less than half your regular sized steak, it is actually that rich!
Wagyu is the breed best known for marbling, it is bred specifically to develop intramuscular fat and combined with centuries of developing farming practices and grain based diets that maximise intramuscular fat growth, there is nothing else quite like it. It's is the only way to reach the crazy marble scores of 9 and above, but marbling (even if significantly lower) still indicates quality with other breeds - a Black Angus with marble score over 2 for example would likely be excellent.
Of particular interest however, is marbling with purely pasture fed beef. It is a grain based diet that usually generates marbling, so when non-Wagyu grass fed beef can achieve marbling it speaks volumes. It indicates that the cattle have been reared on exceptional quality, nutrient rich grass, that they have been well fed, lived a stress-free life and generally been so well taken care of that they have been able to grow big and fat. It indicates that this will be very good quality beef; naturally tender whilst retaining that big, rich beef flavour that is only achieved through a natural free-range grass based diet.