Japanese Kagoshima A4 Wagyu tenderloin

One of the most important and sought-after specialty beef cuts, it is the tender “heart” of the ribeye. This premium cut is located between the 6th and 12th thoracic vertebrae.
When the ribeye is deboned, it yields a clean, oval cut of meat, the finest quality steak, composed of two distinct muscles. It is round like an eye, hence its name, the “eye of the steak.” Its excellent fat distribution gives it exceptional flavor and tenderness.

The history of Wagyu, then, begins sometime in the late 19th century, when Emperor Meiji the Great regained power. From then on, Japan began to develop, transforming from an insular, feudal state into an industrializing superpower. With the restoration of imperial rule, the country’s period of reform (Westernization) also began; Japanese customs and eating habits changed. The ban on eating meat was lifted, and beef took its place in Japanese cuisine. After 1868, as many Japanese became familiar with European and North American customs and everyday practices, eating beef became fashionable in the major cities. Encouraging beef consumption can be seen as part of the new regime’s efforts to reshape the Japanese physique in a way that would make it more appealing to Westerners, thereby helping Japan join the ranks of countries where average height was greater than in Japan. To promote this goal, the government supported beef production and consumption. In 1871, it abolished the monopoly on meat production held by hereditary groups, and in 1872 it publicized both the emperor’s position and the essay by thinker Fukuzawa Yukichi, “On Eating Meat,” as well as related discussions among intellectuals, promoting literary depictions of new ways of life. Thus, although Wagyu beef was developed and is raised in Japan, its incorporation into Japanese cuisine is, in fact, clear proof of Western influence on Japanese customs, marking a significant turning point in Japanese history. 

In the 1880s, the Japanese decided to import cattle from European breeds and crossbreed them with Japanese cattle. In this way, the old draft breeds evolved into beef breeds. Several cattle breeds emerged from these crosses, and they still dominate the Japanese beef trade today. Of these, however, only four breeds are truly Wagyu:

Japanese Black | The Japanese Black breed; its meat is prized for its pronounced marbling. Since 90% of Wagyu come from the Japanese Black breed, when someone says “Wagyu,” they usually mean Japanese Black cattle. 
Japanese Brown | The Japanese Brown breed, a leaner, healthier cattle breed known for the mild flavor of its meat. 
Japanese Shorthorn | Japanese Shorthorn. Although also lean, Japanese Shorthorn beef is rich in inosinic acid and glutamic acid, two valuable acids that give it a more savory flavor. 
Japanese Polled | Japanese Polled: Like Brown and Shorthorn, Japanese Polled is lean, and its meat is renowned for its more pleasant texture and rich, meaty flavor.

In the beginning, there was a black cow
Everything you need to know about Wagyu beef, and especially Kobe beef  
“Wagyu” refers to any cattle raised in Japan or … in the Japanese style. In a loose translation, Wagyu means “Japanese cattle” (“Wa” means Japanese or Japanese-style, and “gyu” means cow or cattle in general). Simply put, “Wagyu” means “Japanese cow.” For Wagyu beef to be classified as Kobe, it must come from a very particular member of the Wagyu breed, called Tajima-Gyu, which is raised under strict protocols in the Hyogo Prefecture.  As Wagyu beef was often transported from Kobe to Yokohama—the commercial port in the Tokyo metropolitan area—it began to be highly prized by the foreigners living there. The slogan “What other, Kobe beef!” is also thanks to its admirers. 

But what makes Wagyu stand out from other types of cattle? And what makes Kobe beef so special that it often commands the highest prices (per kilo) on the market? 
Farmers who raise Wagyu cattle take exceptional care of them. They feed them milk until they are 3 months old. After three months, the calves are fed a mixture of grass, rice straw and grains (corn, soybeans and wheat). Kobe cattle have the same diet as all other Wagyu, but each farm varies the feed it gives its cattle slightly. In addition to corn or cornmeal, which is essential, they add oats, wheat, barley, soybeans, as well as sugarcane silage or cocoa nibs (fragments of the seeds contained in the fruit of the cacao tree). Most animals also eat straw and hay, as they would in their natural habitats. It is worth noting that in recent years, two farmers, one in Japan and one in the Netherlands, have adopted a different diet enriched with a palatable, digestible and safe paste made from pure olive pulp, derived from roasted olive mill “waste.” 

It is sometimes said that farmers massage their cattle to reduce muscle tension caused by cramped quarters.
There are many myths surrounding Wagyu farming. It's said that the cattle live in spa-like conditions, are given "gourmet" food, are massaged with beer, and listen to classical music to help them relax. Although none of these myths has been disproven, that doesn't mean they're the norm. Producers follow very strict farming guidelines, and some have indeed devised special methods that allow Wagyu cattle to live leisurely, peaceful lives. They may listen to music, but it's not necessary. What is certain is that the cattle's calm, relaxed lifestyle helps increase the proportion of intramuscular fat (marbling) and contributes to its unique distribution, which makes Wagyu beef so delicious and sought-after. Its "grain", the fine white streaks of fat, melts as the meat cooks, helping it stay tender, juicy, and therefore flavorful. And because the fat's melting point is lower than the average temperature of the human body, it melts pleasantly in the mouth. 

Part of its appeal is its aroma, a unique, sweet coconut scent. A relatively recent study in the Journal of Agricultural & Food Chemistry identified sixteen compounds that give it this distinctive aroma, ten of which are directly associated with the meat. The strongest evidence, however, comes from compounds derived from fatty acids. The excess fat, its distribution, and the different composition of the fatty acids are due, on the one hand, to a genetic characteristic of this particular cattle breed - as well as to its diet, which is designed to bring intramuscular fat to 30 - 40 % of the muscle's volume - and, on the other hand, to the fact that the calves continue to be raised until they are 30 months old.  

Marbling: What sets Wagyu apart
The results of these breeding methods, combined with longer fattening periods, are the main factors behind the superior flavor of Wagyu meat. Marbling gives Wagyu a better flavor. Its fat melts at a lower temperature than that of any other cattle breed, resulting in a rich, buttery flavor not found in meat from other breeds. This fat is unsaturated and rich in omega-3 and omega-6 fatty acids, which means that marbling not only makes the meat tastier, but healthier too. Despite the breed's genetically increased tendency to develop intramuscular fat, Wagyu also produces a high proportion of unsaturated fats, such as omega-3 fatty acids, which balance out the corresponding proportion of omega-6 fatty acids and therefore help reduce bad cholesterol and combat heart disease. 

Quality grading of Wagyu beef 
Another very important factor that determines the quality of Wagyu is its grade. In some specialist butcher shops or on the menus of high-end steak restaurants, we usually see an A5 rating. This is the grade it has received from members of the Japan Meat Grading Association. Grades indicated by letters from A to C refer to the yield of quality meat from each cow. A is the highest yield grade, and C the lowest. Each letter is followed by a number (from 1-5), which refers to the quality grade: 5 is excellent, 4 good, 3 average, 2 below average, and 1 poor.  
The assessment is based on four criteria:  
1. Marbling (the distribution of intramuscular fat in the meat) 
2. The color of the meat in relation to its brightness 
3. The firmness and texture of the meat  
4. The color, together with the luster and quality of the fat  

As for the «Sashi» categories (i.e., marbling in Japanese), there is also a further assessment, the Beef Marble Score (BMS), with a scale from 1-12. 
According to the BMS, exceptional intramuscular fat is rated from 8-12, good from 5-7, medium from 3-4, the next level down is 2, and the lowest is 1. So A5 is the highest-quality Japanese Wagyu, and consequently the most expensive. The best score an A5 could receive is A5-12, though this is extremely rare. By understanding the logic of this grading system, you can buy or order at a restaurant the meat you want at a price that suits you. 
All of these facts help explain, in a way, why the cost of the finest Wagyu steaks in countries such as the United States easily exceeds $300.  
After all, a (live) Wagyu cow can cost as much as $30,000. In 2002, a Wagyu cow sold in Japan for around $400,000. It was a record, and remains the highest price ever paid for such a cow. 

And Wagyu burgers?  
Is it really worth ordering a Wagyu burger? I would say probably not. The appeal of Wagyu beef lies in its distinctive texture, excellent marbling, and tenderness. So, if the meat is ground and made into patties or burgers, it will certainly be tender, but the difference in taste compared with any other (regular) burger will be slight to barely noticeable.