These oysters can be eaten raw, and whether an oyster can be eaten raw is decided not by how it was grown but by what happens to it after it comes out of the water.

The man farming Matoya Bay worked out, in 1945, that seawater sterilised with ultraviolet light could be used to clean an oyster from the inside. The shellfish are showered with that water for around twenty hours. They are alive throughout, so they go on breathing and filtering, and in doing so they expel the bacteria they had taken in. Nothing is scrubbed. The animal does the work itself.

By 1955 he had patented an apparatus combining ozone with the ultraviolet treatment, which is a considerable distance from anything most people would call oyster farming.

The prefecture certified it as a regional brand in 2002. The season runs from October to the end of March. Through the winter the bay collects what the rivers bring down off the wooded hills behind it, and the oysters feed on that and fatten. So the bay makes them worth eating and the twenty hours afterwards make them safe to eat. Only the first half of that gets talked about. The second half happens in tanks, out of sight, and is the reason the plate in front of you is legal.