So why is wagyu beef so special?
There are two main reasons. The first is the degree of marbling which is higher in wagyu than any other breed. Marbling provide a beautiful full richness and juiciness to the meat. Finely distributed marbling provides a separation between bundles of muscle fibres, increasing tenderness even in cuts that may not traditionally be regarded that way. Marbling tends to be unevenly distributed, with the forend of the animal more marbled than the rear.
The second factor is the composition of wagyu fat.
Wagyu fat has a large proportion of the mono unsaturated fatty acids (particularly oleic acid - the most abundant fatty acid in olive oil). The abundance of monounsaturated fats means that the melting point of wagyu fat is lower than regular cattle - IMF in wagyu is almost liquid at body temperature. Originally this meant a readily available source of energy for long days working the fields and mountains but in the context of eating quality, it means the beef literally melts in your mouth.
A high degree of finely distributed low melting point marbling means that wagyu beef is incredibly tender, juicy and rich but always has a clean finish.
There are several ways to grade wagyu, either done via a subjective visual assessment by trained assessors or objectively via a digital imaging system. The grading systems are heavily influenced by the degree of marbling as it is one of the key indicators of eating quality.
The most common in New Zealand and Australia is a Marble Score from 0 to 9, with an informal 9+ sometimes given to indicate a grade higer than 9.
Beef grading in Japan consists of a letter to indicate yield (A, B, C with A being the best) and a number to indicate meat quality (1-5 with 5 being the best). The meat quality score is made up of an assessment of marbling (the Beef Marbling Standard or BMS, a score of 3-12), meat colour and brightness, meat firmness and texture and fat colour, lustre and quality. The lowest score determines the quality grade.
“A5” is the highest grade and will have a BMS of 8 or above, with excellent scores in all areas.
Objective measurement using the specially designed MIJ-30 digital camera is becoming more frequent. This system automatically calculates and IMF percentage, fineness ratio and measurements of the carcass. Marbling from an imaged carcass will be expressed as a percentage of the ribeye area e.g 30% IMF.
Comparing systems is not straightforward and the subjective systems have a degree of variation within each grade. The Japanese system also goes far, far beyond any other grading system when it comes to marbling.
An AUS/NZ ‘MS9’ will be a minimum of approximately 21% IMF. This corresponds to a Japanese BMS of 3, and a BMS of 12 (the top score) is around 60+% IMF. For comparison the American "Prime" grade corresponds to around 12% IMF.
Kobe beef, along with others such as Matsusaka and Omi beef, is a brand of wagyu, produced under particular strict conditions - for example certified Kobe beef must come from 100%Tajima line cattle that are born, raised and processed within Hyogo prefecture along with meeting strict quality standards.