Mirin is a staple of Japanese kitchens, yet few people know what it actually is.

Although these days it’s thought of solely as a cooking ingredient, mirin was originally regarded as an expensive, high-class beverage. It was the tipple of choice of wealthy ladies, who mixed it with shōchū (distilled spirits) to produce a sweet, heady drink.

Mirin is made by fermenting steamed mochi or short-grain rice with rice kōji (rice malt), and then mixing it with shōchū and letting it mature for 40 to 60 days. The starches in the rice break down into maltose, a type of complex sugar. The mixture then is filtered to produce a golden, sweet, almost syrupy concoction that is reminiscent of Marsala, cream sherry and other sweet fortified wines.

The first mention of mirin was in the 16th century. Besides being a favored beverage of the rich, it was used for otoso, the herb-infused drink that’s sipped to ward off any evil spirits for the coming year during New Year’s festivities. (These days sake is usually used for otoso.) Those mysterious little brown bottles of “health tonic” that are sipped by overworked salarymen are made by infusing mirin with various medicinal herbs, but most people don’t realize they contain mirin at all.

It was not until the early 1800s, in the late Edo Period (1603-1868), that mirin started to be used as a cooking ingredient. In Edo around that time, the type of dark, rich soy sauce that typifies the Kanto area became more popular than the previously preferred light, salty soy sauce from the Kansai area. This dark soy sauce was combined with mirin as well as sake, and later on sugar, to create a new type of Edo cuisine, and dishes that feature this sweet-salty combination of flavors and ingredients are still popular today. These include eel kabayaki, mentsuyu (the dark, rich dipping sauce used for cold noodles), teriyaki and sukiyaki.

For most home cooks, though, mirin continued to be too expensive to use as an ingredient until the postwar period, when taxes on it were drastically reduced and it became more affordable.

There are three types of cooking mirin on the market: mirin seasoning, fermented-mirin seasoning; and hon-mirin, or real mirin. Mirin seasoning, sometimes called aji-mirin, is not mirin at all — it’s an alcohol-free substitute that contains sweeteners (sugar or high-fructose corn syrup), salt and monosodium glutamate. It was created as a cheap alternative to mirin that could be sold in regular grocery stores. Hon-mirin has an alcohol content of around 14 percent, so a liquor license is required to sell it. Fermented-mirin seasoning is real mirin (with alcohol) but with salt and other seasonings added to it, rendering it undrinkable.

Hon-mirin has a sweetness with more depth and complexity than sugar, and the alcohol helps to counteract the gaminess and fishiness of meat, poultry and fish. It’s an indispensable ingredient in all kinds of Japanese dishes, such as the ones already mentioned, to which it imparts a mild sweetness and shiny appearance. Mirin is usually used in cooked dishes, so most of the alcohol content evaporates, but if you’re using it for uncooked dishes like aemono (dressed salad dishes), boil it off at a high temperature first and use the cooled liquid. This method is called nikiri, and is used for sake too.

Mirin-boshi — fish marinated in mirin and soy sauce and dried for a couple of days — is a great way to enjoy the sweet, complex flavor of mirin. The recipe with this article uses horse mackerel (aji), but you can use butterfish (kisu) and similar small fish. Commercial mirin-boshi often contains sugar and other seasonings, which are omitted from this simple homemade version.

Makiko Itoh is the author of “The Just Bento Cookbook” (Kodansha USA). She writes about bentō lunches at www.justbento.com and about Japanese cooking and more at www.justhungry.com.

Recipe: Mirin-boshi (dried marinated fish)

Serves 4

Ingredients

4 fresh small to medium horse mackerel (aji)

3 tablespoons hon-mirin

1.5 tablespoons dark soy sauce (2:1 ratio of mirin to soy sauce)

1 teaspoon grated ginger

salt

sesame seeds

metal skewers

1. Cut the heads off the fish and butterfly them by slicing through the stomach side, opening them up and removing the intestines. Rinse and dry very well with paper towels.

2. Sprinkle the fish with salt on both sides and leave for 15-30 minutes. Wipe off any moisture that comes out of the fish. Combine the mirin, soy sauce and ginger and marinate the fish in the mixture for 15 minutes.

3. Skewer each fish lengthways with two metal skewers and sprinkle sesame seeds on both sides. Leave them in a well ventilated area for 2 to 3 days, turning them occasionally.

4. Grill over a low flame until done and serve with plain rice.

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