Handing Bluefin Tuna
Southern Blue Tuna - Thunnus maccoyii
Region of origin
Juvenile Southern Bluefin Tuna are caught on the continental shelf in the Great Australian Bight region.
Sustainability
Fished under strict government quota controls and management regimes introduced in 1991 (scientists measured the biomass and calculated how much can be taken out in order to protect the specie).
Feed
Southern Bluefin Tuna are still largely fed fresh or frozen small pelagic fishes, and the use of formulated pellets is not yet viable although scientists are currently trying to develop less expensive fish feed. Feeds are designed to replicate the natural feeding pattern of the fish in the wild, delivering a clean, natural taste.
Harvesting method
Wild Bluefin Tuna are purse seine caught in the Great Southern Ocean and ranched in Port Lincoln.
Seasonality
Wild caught between December and February, ranched from February to September.
Size
On arrival from the wild harvest to the ranching operations, the Southern Bluefin Tuna average 15-20kg in size. By completion of the 6-9month ranching, they may be as large as 50kg, mostly averaging 35-40kg.
Methods to market
Although some fresh Southern Bluefin Tuna may be available between April and September, it is mainly sold in frozen speciality cuts, typically carrying their traditional Japanese names – otoro, chutoro and akami.
Akami literally means ‘red meat’, and comes from the top loin, shoulder and tail of the fish. It’s the most abundant part of the fish, which makes it less expensive than the other cuts. A lot of people prefer akami because it has a clean, bright flavour and vibrant colour.
Otoro means ‘big fat’ in Japanese and that’s what it is – a piece of well-marbled otoro looks like a top-quality waygu steak, and comes from the fatty belly section of the fish.
Chutoro means ‘medium fat’. And comes from the area of the belly fillet behind the otoro – slightly lighter in colour than the akami.
Handling and storage
Fresh fish should be kept in whole form for as long as possible and only fillets removed. Frozen loins or cuts should be defrosted at room temperature and used as soon as possible. Both fresh and frozen fillets should be allowed to ‘bloom’ at room temperature without any cover, prior to serving – developing their colour and allowing the intermuscular fat to soften. Unused fillets should be wrapped tightly in Japanese rice paper, then wrapped tightly in plastic wrap and buried under ice in a leak proof container.
Flesh colour
The colour of the flesh varies by cut Otoro – marbled pink in colour Chutoro – pale pink/white in colour Akami – deep rich red in colour. Consistent across all Southern Bluefin Tuna, the fish will bloom into full colour soon after cutting and maintain the premium colour for approximately four hours only if not refrigerated. If placed in refrigerator it will maintain its full colour for 8-12 hours.
Flesh fat content
The Southern Bluefin Tuna are harvested specifically to maximise the fat content at its peak – approximately 50% in the otoro and 18% akami
Flavour
The aroma is distinctive with a deep, yet clean smell that is slightly full flavoured. The flesh from the various parts of the fish display unique
characteristics:
Otoro has a sweet rich buttery flavour and long lasting umami finish.
Chutoro is slightly less sweet but has a clean, full flavour.
Akami is a lighter, simpler flavour with light sweet note on the front palate.
Cooked Southern Bluefin Tuna is characterised by it’s amazing meaty umami reminiscent of pork crackling with an underlying nuttiness of fresh baked bread.
Flesh Texture
Soft to medium – the flesh has distinctive knots. As with the flavour profiles, the texture will vary by cut of the fish:
- Otoro is soft and yielding in the way of butter.
- Chutoro has a slightly firmer texture, similar to a fresh mozzarella cheese.
- Akami has a crisp texture, similar to raw salmon.
Yield from Whole Fish
Skin-on boneless fillet yields approximately 65% flesh of which 10% is otoro, 20% chutoro and 70% akami.
Culinary applications
Southern Bluefin Tuna is a luxury – an extreme eating experience which carries unique and special characteristics. Best served raw or cooked using wet methods to avoid drying. The unique culinary characteristics of the bluefin are best enjoyed raw or just warm.
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1.The top loin is known as akami grade |
2. the bottom |
3. The fatty otoro with its |
4. To prepare the otoro and |
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5. The three grades |
6. The loin is broken into |
7. Remove the top triangle |
 8. Cut loin vertically toproduce classic ‘saku’ blocks for sashimi and sushi slices |
