Why did I find a piece of bone in my tuna saku?

A customer gave us the following review: “Very poor management of the fish when cutting into these blocks. Bones were found which just should never happen."

We replied as follows

Hi Robert

I saw your review and wanted to explain how and why this arises. It's very rare.

How?
The bluefin is cut into loins (essentially big chunks) weighing 5 or more kilos and frozen to minus 60. This happens in Majorca within hours of catching.
We receive it in this form and keep it at minus 60. We withdraw the loins from stock and use a bandsaw to cut them, whilst still frozen, to retail formats, eg large fillet steaks, small sakus, and so on.
This process is carried out very quickly to minimise the time the tuna spends above  minus 60. We return it to minus 60 until we despatch to you.

It is impossible to tell if there is a bone  in a piece of tuna frozen at minus 60, even if you are cutting it into small sakus. You might suggest we should be able to see a white bone in the red meat. However, the super cold tuna surface frosts up immediately on exposure to the (chilled) cutting room temperature - ie the red tuna gets a white frosting.

Thus, if the filleter in Majorca has left a piece of bone lurking in his fresh loin, it is not going to emerge until our customer discovers it. The filleters in Majorca are good but not perfect. They do very occasionally leave a piece of bone in the loin.

Why don't we find an alternative way?
We could in theory defrost the tuna and cut it "fresh" with a knife. Then we would find any small pieces of bone that shouldn't be there. But the eating quality of the meat would thereby be downgraded. So we have taken the awkward decision of accepting that very occasionally some customers will complain to us as you have done, and we will refund them, as a superior option to degrading the eating experience by defrosting and refreezing.

We have sold over 8,000 bluefin saku blocks since we started running the Majorcan bluefin. We have had about 8 complaints about bones.

How does your other supplier manage to give you bone free sakus? Clearly his tuna is defrosted at the point of cutting the sakus. We don't go down this route because we are committed to delivering the highest quality FROZEN fish to our customers, even if there are occasional downsides.

I hope this helps you understand how we erred with your saku block.

Yours
Alistair Blair