Rinse well, then tear the leaves apart. Discard the stalks.
In a pot (do not use aluminum), boil 1500 ml of water, then add the shiso leaves and simmer for 7 to 8 minutes, stirring occasionally with chopsticks.
Line a colander with a paper towel, then strain the juice from Step 2, and return to the pot.
Add 100 g sugar to the pot, then heat. The juice should be a dark red color.
Add 100 ml vinegar, and the color should become more reddish.
It's ready after it comes to a boil. Skim any scum that rises. Drink after cooling.
Store in the refrigerator. If you store the shiso juice in the used up bottle of vinegar, it will last longer.
Story Behind this Recipe
Every year, I whip together low sugar shiso juice, and since it pleases my friends whenever I share it with them, I figured this year, I'd publish the recipe. It's a mildly sweet, healthy shiso juice that you can drink as is.
If it's too troublesome to strain the leaves in Step 3, you can omit that step, but straining makes it look nicer. Add sugar to taste. If it's too strong, dilute with carbonated or plain water. You can use the leftover shiso leaves for cooking. The vinegar aroma is strong right after steeping, but will fade after the leaves cool.