So we have the shiso leaves, washed and plucked from their stems. But (as mentioned in the previous post), they can't just be thrown into the ume pickling crock. There is a critical first stage: we have to get the "aku" out...
For a couple of bunches of shiso, you use 40g of salt (the same sea salt we use for most of our pickles). You take half the salt and start squeezing it into the leaves. At first it seems like nothing is happening, but slowly the salt starts to draw the moisture out of the leaves. As you continue kneading and rolling, slowly more and more of that juice comes out.
The liquid has a purple colour, but with a distinctively dark muddy frothy tinge: this is the aku, the bad stuff (more on aku at the bottom*). And you just tip it away.
Then you do the same again: more salt; kneading and rubbing until a whole lot more juice comes out — more than you can imagine is actually in the leaves. This (below) was the second round of aku. It too got chucked away.
Now the shiso is ready and primed, it's time to open up the pickling crock again... This is what the ume look like after 3 weeks pickling: a much brighter yellow, and giving off a wonderful fruity aroma that is close to being apricot.
Then we take out half a cup of the ume liquid (shiro-umezu)...
…and pour it over the shiso leaves.
Now when you knead the leaves some more, the colour that comes off them is a beautiful clear scarlet. This is one of the magic moments of the entire umeboshi process — not least because of the wonderful heady mingling of aromas that rises.
Next the leaves are packed over the top surface of the ume...
And finally the remaining red shiso liquid is poured over everything so it seeps down to the bottom.
Back on goes the drop-lid (and the top lid and the paper cover over the top). But no need now for any plastic film; no need for spraying with shochu either: not only has the ume crock developed its own strong (and salty) ecosystem, the shiso leaves serve to add their own powerful antibacterial properties ...
Over the next three weeks or so, the colour from the shiso leaves will permeate the umezu and the fruit, turning them that beautiful umeboshi red.
All there is to do now is to wait some more. The shiso is a powerful dye, but the colour on your hands will be long gone by the time the next stage comes along…
*A bit more about the "aku". This is a word used quite a lot in Japanese cooking to express a number of different ideas. It's the word for lye (灰汁, sometimes read as はいじる hai-jiru). But it also refers to brackish off-flavours in food that need to be removed by a preliminary process — such as scalding and draining, or salting and leaching.
Basically though, it just means "bad stuff." You're not getting rid of nutrients, but you are getting out the stuff that prevents enjoyment of the full inherent flavour of the finished product.
[The next step, the drying game, continues here…]