Umeboshi ("dried ume") are pickled ume fruits common in Japan. Ume is a species of fruit-bearing tree in the genus Prunus, which is often called a plum but is actually more closely related to the apricot. Umeboshi, which are a popular kind of tsukemono (pickles) and are extremely sour and salty, are usually served as side dishes for rice or stuffed inside of rice balls (sometimes without removing their seeds inside) for breakfast and lunch, and are occasionally served boiled or seasoned for dinner.
Umeboshi are traditionally made by harvesting ume fruit when they ripen around June and packing them in barrels with salt. A weight is placed on top and the fruit gradually exude juices, which accumulate at the bottom of the barrel. This salty, sour liquid is marketed as umezu ("ume vinegar"), although it is not a true vinegar.
Most modern umeboshi are made by using less salt and by pickling the ume in a seasoned liquid or vinegar. They are typically dyed red using purple perilla herbs (called akajiso), or flavoured with katsuobushi, kombu or even sweetened with honey. Because modern methods of preservation use less salt, they usually contain an artificial preservative to extend shelf life.
Nattou is a traditional Japanese food made from soybeans fermented with Bacillus subtilis. It is popular especially as a breakfast food. As a rich source of protein, nattou and the soybean paste miso formed a vital source of nutrition in feudal Japan. For some, nattou can be an acquired taste due to its powerful smell, strong flavor, and sticky consistency. In Japan nattou is most popular in the eastern regions, including Kantou, Touhoku, and Hokkaido.
Nattou is made from soybeans, typically a special type called nattou soybeans. Smaller beans are preferred, as the fermentation process will be able to reach the center of the bean more easily. The beans are washed and soaked in water for 12 to 20 hours. This will increase the size of the beans. Next, the soybeans are steamed for 6 hours, although a pressure cooker can be used to reduce the time. The beans are mixed with the bacterium Bacillus subtilis natto, known as nattou-kin in Japanese. From this point on, care has to be taken to keep the ingredients away from impurities and other bacteria. The mixture is fermented at 40°C for up to 24 hours. Afterwards the nattou is cooled, then aged in a refrigerator for up to one week to add stringiness. During the aging process at a temperature of about 0°C, the Bacilli develop spores, and enzymatic peptidases break down the soybean protein into its constituent amino acids.
Historically, nattou was made by storing the steamed soy beans in rice straw, which naturally contains B. subtilis nattou. The soy beans were packed in straw and then left to ferment. The fermentation was done either while the beans were buried underground underneath a fire or stored in a warm place in the house as for example under the kotatsu.