The art of Sushi: using wasabi to kill parasites

Question

I've been to many sushi places and last night I went to a place that I've been to before (not that long ago either). When the sushi came, we noticed that it had wasabi spread on the rice, under the fish.

When we complained we were rudely told that the chef had been doing sushi for 30 years and wasabi is used to kill parasites in the fish.

This is believable since I know in some countries, red peppers are used in foods all the time for the same reason.

However, my understanding of sushi is that the chef is a craftsman who not only picks great fish, but also knows how to find and remove parasites.

My question is, is this normal? Is it proper for the Sushi chef to add wasabi to the sushi to help prevent parasites? If so, how come I've only encountered this practice once out of the many sushi places I've frequented?

Answer

This is perfectly normal, however, I find the common claim that "it is to prevent parasites" a bit dubious (I would think that it would have to be uniformly applied to the entire fish to have any measurable effect). The wasabi is really there to add flavor. In really high-end sushi restaurants in Japan, for example, it is relatively uncommon for the guest to be served a mound of grated wasabi. Instead, the chef applies the perfect amount of wasabi to each piece of sushi. Some chefs will not even serve soy sauce, instead individually brushing on the sauce on each piece. If wasabi is served separately from the fish, it is generally also considered bad form to mix it with the soy sauce (as is commonly done in the US).

Edit: To answer your question about why you've never seen this practice before, here are some possible explanations:

1. It takes more time/skill/effort to do it properly.
2. Many sushi restaurants in the US do not have properly trained sushi chefs. In fact, in most areas of the country with little or no Japanese population, don't be surprised if your sushi chef is a Salvadorian who learned from the Oaxacan who learned from the Korean owner of the restaurant. Not that there's anything wrong with that; one of my favorite sushi places is run by an Indonesian. Just keep in mind that the people making you your sushi may have never experienced the "real thing" themselves.
3. "Real," fresh wasabi is very rare and expensive. Most of the stuff that is used in the US is basically horseradish paste plus food coloring. Restaurants that can both procure and afford to use the real stuff will want to use it sparingly; they wouldn't want to waste it by putting a mound of it on each plate. Therefore, they might be more inclined to use the "proper" technique.

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