Irizake is an old Japanese seasoning used during the Edo period, which is made by putting umeboshi (pickled Japanese apricot) into Japanese sake (rice wine), and boiling it down.
It is said to have originated at the end of the Muromachi period, and is a liquid seasoning which was widely used until the mid-Edo period, along with tare (sauce made with soy sauce, sake, and other seasonings). As the use of soy sauce spread from the mid-Edo period, irizake gradually became used less often and is now not generally used. As it does not have a strong taste like soy sauce and makes good use of the flavors of its ingredients, it goes well with sashimi (fresh slices of raw fish) made from white fish and shellfish. The seasoning briefly fell out of use completely, but has come to be reevaluated in recent years and is increasingly used as sauce for sashimi in high-class Japanese restaurants.
Place one rather large umeboshi into 1 go (180ml) of Japanese sake and put on the heat. Lightly break up umeboshi to cause the flavor come out, and reduce over a low heat until it halves in volume. Filter out the umeboshi with a dish cloth or tea strainer, and leave in a cool, dark place for one to two days in order to bring out its flavor. It can be preserved for approximately two weeks if it is kept in a refrigerator.
The above is a recipe closest to that of the original form of the seasoning, but there are other recipes which include steps such as the addition of irigome (parched wheat or rice), dried bonito and kelp before reducing in order to add flavor and body to the sauce. Mirin (sweet cooking sake) and salt are also sometimes added. For best results, junmaishu (sake made without added alcohol or sugar) and old-fashioned salty umeboshi pickled in only salt and red shiso should be used.
"Ryori Monogatari" (tale of food) records that 'Irizake is made by putting 15-20 umeboshi, 2 sho (approx. 1.8 liters) of old sake, a little water, and a little tamari (rich soy sauce) into 1 sho of dried bonito before reducing it down to 1 sho, filtering it and cooling it, while there are some people who add 2 sho of sake and 1 sho of water before reducing it down to 2 sho; Nidashizake (extracted sake) is made by adding a little salt to dried bonito and boiling it for a while with new sake, filtering it and cooling it; and shojin irizake is made by putting chopped umeboshi and hoshi kabura (dried turnips) into grilled tofu with size of dengaku, and boiling it with old sake.'