The origins of the wasabi horse-radish (preferably from the Izu peninsula), miso paste (preferably from the Nagano mountains) and pickled ginger (preferably from Tochigi) will all be scrutinised. Rice is expected to be the most frequent area of failure: a true sushi master will insist on Japanese koshihikari rice grown in Japan.
The same variety grown in California might, just, be acceptable. Faux pas may include serving Chinese soy sauce, or miso soup in a porcelain cup.Meanwhile, bluefin tuna used in sushi has been found to contain terrifying amounts of mercury, at least in the US.
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