Nikiri Sauce
From http://www.trevorcorson.com/sushi-arsenal.html, The Story of Sushi, copyright © 2007 by Trevor Corson

Most sushi bars put out bottles of soy sauce, as well as a small dish for soy sauce for each customer, and most Americans think they are supposed to dunk all their sushi in the soy sauce. But full-strength soy sauce overpowers the delicate flavors of raw fish.

A good sushi chef adds all the flavoring the sushi needs before he hands it to the customer. He mixes his own sauce and brushes it onto the sushi behind the bar. This sauce is called nikiri, and it consists of soy sauce augmented with bonito-and-kelp broth called dashi, sake, and the sweet rice liquor called mirin. A sushi chef who uses nikiri instructs the customer not to add extra soy sauce. Some serious sushi connoisseurs forgo soy sauce in any case, preferring to concentrate on the subtle flavors of the fish. If you eat at a high-end sushi bar and the sauce in your soy-sauce dish is a translucent, light shade of brown, it's probably nikiri. Pay attention to its complex, subtle taste.

If you're feeling ambitious, you can make nikiri sauce at home. You'll be astonished at how delicious it is. You'll need five ingredients:

Soy sauce
Dried kelp (konbu)
Dried bonito fish flakes (hana-katsuo or katsuo-bushi)
Sweet rice wine for cooking (mirin)
Sake

I start with real soy sauce—not the stuff you get at the supermarket, which has been quickly manufactured in factories, but true soy sauce, that has been aged for two years and hasn't been pasteurized. My favorite at the moment is Sakurazawa Yuuki Shoyu, sold by Mitoku; you can purchase it from Simply Natural Foods. The taste is richer and more layered than typical supermarket soy sauce. This soy sauce should be kept refrigerated.

Next I make dashi, a broth that is one of the pillars of Japanese cuisine; for example, it serves as the base for miso soup (see below). Any Japanese cookbook will include dashi-making instructions. Dashi starts with strips of dried kelp (called konbu), which you can purchase at many gourmet food stores and most Asian ones. I put the kelp in water over medium heat. Just before it boils I turn off the heat. (If it boils the broth will taste bitter.)

Then I sprinkle in dried bonito fish flakes called hana-katsuo or katsuo-bushi; they look like wood shavings. Gourmet and Asian food stores sell them. In The Story of Sushi I describe the extraordinary method by which these are made; it involves locking smoked tuna up in boxes until they're covered with mold. After five minutes I strain out the kelp and fish flakes. The broth that's left is dashi.

Another ingredient is mirin, a sweet rice cooking wine that is also a pillar of Japanese cooking. Mitoku sells a traditionally aged version that I like, also available from Simply Natural Foods.

In a pot, mix ten parts soy sauce, two parts dashi, one part mirin. Then throw in one part sake, and simmer the mixture briefly. You've made nikiri!

In addition to nikiri sauce, there are several exotic Japanese condiments that I like to include when making sushi. These condiments add flavors to the sushi experience that are unfamiliar to most Americans, and they'll set your sushi apart.

Other Japanese Condiments

Trevor's recommendations:

• An alternative to nikiri sauce is ponzu sauce, a fantastically flavorful combination of soy sauce, the sweet rice wine mirin, brown-rice vinegar, kelp broth, and the Asian citrus fruit yuzu, which is a bit like a grapefruit but has its own unique taste. Put a pinch of chopped chives atop a tuna nigiri and then drizzle on a few drops on ponzu; it's divine. I buy Mitoku's version of ponzu sauce, from Simply Natural Foods.

• Another condiment that involves the Asian citrus fruit yuzu is yuzu koshou. It's a greenish mash of yuzu and hot pepper, and is only available from Asian food suppliers; it's often labeled in English as "citrus puree." On sushi it should be used sparingly. Instead of wasabi, a tiny dollop of yuzu koshou atop a whitefish nigiri makes for an unusual but heavenly combination of flavors.

• Pickled plums—umeboshi—are exceedingly popular in Japan. When you're making sushi rolls, a fun alternative to tuna, cucumber, or avocado for the roll's filling is umeboshi paste. A little will go a long way; it's a sour taste but wonderfully pungent. For Americans who love sweetness, it may take some getting used to, but in moderation it will bring a refreshing zing to your sushi.