Use a toothpick to carefully remove any trace of stems from the plums, being careful not to puncture the skin.

Soak the plums in cool water for a few hours or overnight. Drain well.

Fill a wide shallow bowl with vodka or spirits.

Add 30 ml (2 tablespoons) vodka to a quart-sized mason jar, close lid, and slosh around all the insides to sanitize it. Dump out vodka and set jar aside to air dry.

Measure salt, using 10% of the weight of the plums.

One small batch at a time, add plums to the bowl of spirits, rolling them around to sanitize them.

Build layers up in the jar. First, add salt (estimating the amount to add based on total batch size. Then add a layer of sanitized plums (letting them drip dry of spirits for a moment first). Then add a layer of now-wilted shiso leaves.

Repeat layering- salt, ume, shiso, until all ingredients are added to the jar.

Add weights (sanitize them first) to top of jar to encourage brine to form.

Cover tightly with lid.

The brine should form in the next few days so that the contents are completely submerged.

After 1 to 4 weeks of being submerged in the brine, find a time window of 3 days in which the forecast will be sunny and dry. (This is typically mid to late summer).

Strain the jar contents over a bowl, capturing the brine (now known as umeshu-- plum vinegar). Pour into a jar and save for later.

Separate the shiso leaves from the ume. Spread both out onto a single layer in a colander (you may need more than one), and place that over some newspaper sheets (so they don’t stain the table).

Shake the plums around once a day during the three day drying period.

After three days, the skins of the ume will be dry and fuzzy.

Sanitize a few jars with vodka (one or two pint-sized jars should suffice). Let jars air dry.