Change Your Concept of Raw Oysters! Small but Sweet, Savory Tasting Kunisaki Oysters


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“Kunisaki Oysters” are characterized by a sweet taste and their light aftertaste. Designated as a regional specialty brand of Kunisaki city in Japan’s Oita Prefecture, these Kunisaki Oysters have emerged through collaboration between the city, the local fishermen and Yanmar. In Y MEDIA, today, we will take you through the story of how the Kunisaki Oyster came to be and give you a detailed explanation of what makes them so unique.

Raw oysters farmed Western-style and with a crisp texture and rich and mineral flavors.

The culture of eating oysters by in a hotpot or fried, is widespread in Japan. Therefore, oysters are mainly circulated in shucked form and with a focus on the size of the oyster. Even when buying raw oysters from stores, customers favor larger and meatier oysters. However, in the West, oysters are mainly consumed raw. The raw oysters are served in their shells, as a side dish, allowing the diner to savor the taste and mineral characteristics more directly.

Kunisaki Oyster are small, which makes them suitable for western style cuisine, and the shape of the shell itself has a singular beauty. Kunisaki Oyster are well known in Japan for their suitability for consumption raw, where they reveal an original and distinctive, fresh taste. Hailed as “black gems” because of the carefully nurtured, alluring shells, raw oysters are being increasingly served in Michelin star restaurants and popular oyster bars.

The oysters farmed using “single seed method” have beautifully shaped shells and are thick and meaty.

Kunisaki Oyster uses a different aquafarming method from that used in other regions. In established oyster farming regions such as Miyagi and Hiroshima, oysters are farmed by attaching the oyster larvae to a substrate formed by stringing together scallop shells and submerging them in the sea, and then moving them to a region with a high plankton density.

However, Yanmar Marine Farm in Kunisaki utilizes the single-seed method in which spats or seed oysters are cultivated by distributing the oyster larvae one by one until maturation.

(Left) Mr. Motokazu Kato (Group Divisional Manager at Yanmar Marine Farm) has been involved in oyster research for more than 30 years, and often calls himself “oyster crazy”.
(Right) Aquafarming cages from Australia used in the single-seed method. These cages prevent the oysters from sticking to other objects.

Cultivating oysters using the single-seed method has three major advantages. The first is that the oysters are free to move within the cage, and don’t adhere to objects or surfaces that may cause odors or impart unfavorable taste to the oyster. Because of this, Kunisaki oysters are able to realize superior taste and high-quality. The second advantage is that by using “pedigreed” seed oysters produced in-house, thorough management of their growth has become possible. The third and greatest advantage is that because most of the aquafarming process is controllable, the size of the oyster meat and the shape of the shell can be modified as desired.

The cultivation method — offshore spots and tideland are used in accordance to the situation of the sea and growing conditions of the oysters.

Oyster farming was a completely new initiative for the city of Kunisaki. The local authorities at Kunisaki City were concerned at the decrease in the fishing population and consulted Yanmar on how to utilize the now empty cultivation lands. Thus was the Kunisaki Oyster born, in 2013.

In the search to find a cultivation method appropriate for Kunisaki, it was decided to employ the tide and deep method in which takes advantage of areas known as tidal flats, that are low-lying flat coastal areas, regularly inundated by the tides. In this efficient method, oysters are grown in the tidal areas during season where water temperatures are high to obtain an original taste and create a shell that grows stronger oysters. Then, the oysters are moved to deeper offshore waters when the water temperature drops, letting the oysters feed sufficiently, resulting in meaty oysters.

By using two different fishing grounds, that is, the tidal flats and the offshore zone, the natural characteristics of Kunisaki Oysters are developed, cultivating oysters that are full of meat and have beautiful shells.

(Left) Appearance of an oyster after maturation. Even in the single-seed method, deposits are unavoidable, to some extent.  (Right) Locals carefully remove the deposits on the oysters one by one.
(Left) Appearance of an oyster after maturation. Even in the single-seed method, deposits are unavoidable, to some extent.
(Right) Locals carefully remove the deposits on the oysters one by one.

A production system that includes the rearing of seed oysters, cultivation, cleaning, and shipping guarantees the safety of the oysters

With a never-before-experience raw oyster taste and refreshing texture, the Kunisaki Oyster has garnered legions of fans among professional chefs and restaurants. While many outlets do not want to deal in oysters because of the risks surrounding them, including the taste, the Kunisaki Oyster has become the oyster of choice for many famous restaurants. At this point, Ms. Terai (Quality Control manager) introduced us to the quality control technology which is employed at the Yanmar Marine Farm, and highly appreciated by those who do not compromise on quality.

Restaurants have been steadfast in their praise of the safety of Kunisaki oysters.

In Japan, most consumers still eat cooked oysters, and there are many who are apprehensive about eating oysters raw. In the three years since shipments began, Kunisaki Oyster has not had a single food-related incident where the oysters were found to be the cause. Restaurants have been steadfast in their praise of the safety of Kunisaki oysters. It is all because of the thoroughly implemented quality control technology used at Yanmar Marine Farm.

From the viewpoint of food safety and hygiene, at present, a technology that eliminates the Norovirus does not exist. Therefore, producers are left with the problem of how to improve the safety of their products. With the cooperation of Oita Prefecture and Kunisaki city, periodic inspections are conducted in cultivation grounds to check levels of food poison causing viruses and bacteria including Norovirus.

If the level of bacteria exceeds a certain threshold, cultivation of oysters is prohibited from those areas. In such areas, cultivation can only be restarted after the cultivated oysters are thoroughly cleaned and their safety is verified. However, data collected to date allows producers to identify certain trends or factors, such as particular bacteria that do not occur in winter. Using this information, areas where contamination is predicted can be avoided, resulting in improved safety.

Once the oysters are matured, they are removed from the sea and preserved in a marine tank on the land where inspections are carried out. Only oysters that pass the inspection are shipped. Lastly, before shipping, safety is further guaranteed by cleaning the oysters using the seawater that has been filtered through filters finer than the size of a virus.

Oysters that test negative to the presence of bacteria or viruses are scheduled to be shipped next day and are further cleaned using a special purification system for 20 hours. One oyster is capable of taking in and discharging tens of liters of seawater in one hour, thoroughly washing their bodies of bacteria.

Once washed, each lot of oysters is checked for verotoxin producing bacteria such as common bacteria, E. coli, Vibrio parahaemolyticus, Norovirus, and O157. Moreover, close attention is paid to prevent oysters from possible contamination due to human contact at the final stage. Personnel having sick family members are not allowed to take part in the shipping process.

Only oysters which are verified as safe in this strict inspection and cleaning regime are shipped. Of course, such diligence takes time; we take such care because we want to deliver oysters that our customers can eat without worry.

(Left) Final inspection of oysters. Oysters that do not fulfill the quality standards of “Kunisaki Oyster” are not shipped.
(Right) Oysters are arranged one by one with the cup-shaped shell on the bottom. As hardly any seawater spills from the oyster’s shell during transport, oysters do not dry or deteriorate.

“From Catching to Cultivating”. Aquafarming for the next generation

Kunisaki Oyster was bom with cooperation of local fishermen and Kunisaki city, where the fish catch was in decline. Now, Kunisaki oysters have been selected as a gift in return for local tax contributions in the Japanese “Furusato Nozei” system. Thus, the oysters have grown to be able to contribute to the regional economy. Japan is surrounded by the sea, and fishery is one of its most important industries. With Yanmar’s technological prowess and the vitality of the private sector, we hope to lend a hand to help Japan’s fishery industry “From Catching to Cultivating” by restoring its strength in the local community.