Using their own variation of the traditional methods used in Ryujin for centuries, the Sogawas make a mellow, tasty pickled plum that has less salt than typical Japanese pickled plums. The process used by the Sogawas is technically known as "lactic-acid fermentation," one of the oldest and safest ways of preserving food. "The secret to making good pickled plums," says Sogawa, "is getting lactic-acid-forming bacteria (the desirable type) to grow before other competing bacteria have a chance to multiply." While lactic-acid bacteria are salt-tolerant, many undesirable species are not. To help establish beneficial bacteria, traditional makers use the proper amount of salt, and store the fermenting plums in a cool, dark place. Lactic-acid bacteria multiply rapidly under these conditions. Once flourishing, they produce enough lactic acid and carbon dioxide to create an acidic environment that further inhibits the growth of undesirable microorganisms and enzymes. The carbon dioxide also contributes to a favorable anaerobic (low oxygen) condition and further stimulates the growth of lactic-acid bacteria.
At Ryujin, plums are picked around the end of June, when they are still green and their juice is at its peak of acidity. This guarantees the umeboshi to have as tart a taste as possible. "If they are picked too early," says Sogawa, "they are too hard, and their color never changes from green, but if left too long on the branch, the resulting pickles will be soft, mushy, and tasteless."
By the last week in June, the activity at Sogawa's shop is intense and non-stop from dawn to dusk. All the plums reach their full size at the same time and must be picked within a week or two. Any delay means the plums will begin to ripen, reducing their acidity, flavor, and medicinal qualities.
Next, the harvested plums are washed and then soaked overnight in water to remove any bitterness. The following day, the soaked plums are placed in large vats. A layer of jade green plums is topped with glistening white sea salt, followed by another layer, then another until each vat is filled with 5,500 pounds of plums and 638 pounds of salt. This brings the salt content to about 12 percent. In earlier times, before the link between strokes and salt consumption was clear, the salt content of pickled plums was over 25 percent!
The salt immediately begins to draw out the juice from the plums. A flat pressing lid topped with a heavy weight is placed on the plums to keep them submerged in the liquid. As the salt penetrates the flesh of the fruit, the pickling process begins; the plums are left to ferment until the end of July (the end of the rainy season). Taken from the vats, the pickled plums are placed on wooden racks and left outside to dry for anywhere from four to seven days, depending on the weather.
Although the pickling process is now complete, the wrinkled and shriveled plums do not have the dramatic red color and aromatic flavor of Mitoku's prized Ryujin organic pickled plums. To make these finest umeboshi, Sogawa must soak the plums in plum vinegar along with leaves of the beautiful, scented red shiso (perilla) plant.
An herb that is related to mint, shiso has a slight lemony taste yet a unique flavor of its own. Its red, heart-shaped leaves are reminiscent of red meat, hence comes one of its English names, "beefsteak plant." Besides adding color and flavor to umeboshi, shiso has strong antibacterial and preservative qualities both in the pickling process and on the person who eats them. It is this that makes shiso such a perfect garnish in the sushi shop.
To add the essence of shiso leaves to his pickled plums, Sogawa mixes the leaves with the liquid (brine) that is left from the pickling process. The shiso leaves turn the liquid a brilliant red, and the umeboshi are left to steep in this liquid for five days. When the plums are removed from the plum vinegar, they are placed in vats and left to age for up to one year. The remaining red liquid is bottled and distributed by Mitoku as Ryujin Umeboshi Vinegar.