I was told that “Shio-koji” 塩麹 is “all the rage” in Japan. Although preserving or marinating vegetables and fish in salt and “koji” is a very old technique, it appears to have made a big come back. I resisted jumping onto the band wagon, until I succumbed at the first sighting of a package of dried koji at the local Japanese grocery store.
Digression alert: Before fermentation can happen, complex carbohydrates or starch have to be converted to fermentable sugars. All cultures somehow figured this out to make alcohol. The most primitive form is to chew cooked grains and spit the masticated starch out into a vessel. Diastase in saliva will convert starch into sugar and fermentation can produce a primitive “jungle” beer. For true beer making, enzymes formed during sprouting of barley (malting) is used to convert starch in the barley and other grains to sugar (“mash). The Japanese/Chinese figured out that certain mold (yes, “mold” called Aspergillus oryzae, which produce several enzymes including amylase) can convert the starch of cooked rice into fermentable sugar. Many Japanese food items are based on “Koji” to produce; sake 酒, chochu 焼酎, miso 味噌, and shouyu 醤油 (soy sauce). But koji or cooked rice inoculated with this mold by itself can be used in different dishes. If this was used in pickling or “tsukemono” the vegetables, sugar will mostly ferment into acid (lactic acid by lactobacillus) rather than alcohol. Thus, it imparts sweet (sugar), sour (from lactic acid) and salty (from added slat) and additional “je ne sais quoi” components from whatever develops during fermentation.When I was growing up in Hokkaido, there was a fermented and preserved condiment/side dish called “Nishin-zuke” 鰊漬け or Herring pickles (picture below) and my mother used to make it. Essentially, vegetable and filets of dried herrings were mixed with “koji” and salt and left to ferment for several months in a cold place (there were many “cold” places in winter in Hokkaido houses).
After a few hours, the dried koji absorbed the water and swelled up (#3). I left this container with a lid lightly sealed (with some gap to let the gas escape) on the kitchen counter (room temperature) for 9 days mixing it once a day (#4). It developed some viscosity with a faint slightly sweet smell and the rice kernels got soft and could be crumbled between finger tips easily (#4). I pronounced this “done”, put the lid on tightly and moved it to the refrigerator. According to the instruction sheet, this final product will last at least 6 months in the refrigerator. I suspect you will be seeing this in future preparations.