Shiokara is a preservable food made by salting and fermenting seafood meat and internal organs. The internal organ itself produces enzyme that starts the fermentation, but also rice malt is sometimes added to accelerate the fermentation.
The saltiness goes well alcohol, and is a common side dish served at informal drinking place. The taste also matches the rice, and is also eaten as ochazuke, which is a type of dish which can be quickly made by pouring green tea on rice.
The name shiokara appears in an old literature from the Heian period (794-1185). But shiokara from the Heian period cannot be identified as the same one in the present period, and it is said that only after the middle of Edo period (1603-1867), the name and food shiokara became popular.
The most common type of shiokara eaten is ika-no-shiokara meaning squid shiokara. The most famous place that produces ika-no-shiokara is Odawara city, Kanagawa prefecture. It is believed that shiokara first became known in the Sengoku period, which is from the end of 15th century to the end of 16th century.
A pickle shop owner whose name was Minoya Kichibe lived in Odawara city, but his business was not going well because he was a drunk. However, he pickled squid with salt and rice malt, and the food started to become popular, and became a local speciality of Odawara.
Other than shiokara made with squid, there are other kinds of shiokara too. For example, octopus shiokara is sometimes fermented together with Japanese horseradish, and is called takowasabi, because tako means octopus, and wasabi means horseradish.