A shrub is an old fashioned drink, either alcoholic or not, containing some degree of vinegar. The following shrub recipe makes a refreshing non-alcoholic drink composed of a herb syrup and a herb infused vinegar, the herb being Japanese knotweed. There are endless ways to make a shrub but they should all be somewhat fruity and somewhat acidic.
Japanese knotweed (JKW) is not a fruit, it is a remarkable invasive medicinal and edible perennial weed which looks a little like bamboo and belongs to the Buckwheat plant family. Being a close relative of rhubarb it can be used in foods with that flavour in mind.
Infuse the vinegar:
Infuse a jar full of clean chopped JKW leaves and stems in apple cider vinegar for a couple of weeks.
Strain and bottle.
Make the syrup:
Simmer a cup of sugar, a cup of water and a couple of cups of clean chopped knotweed leaves and stems for about 20 minutes.
Cool, strain, bottle.
Make the shrub:
The exact ratio will depend upon the sweetness of your syrup and the sourness of your vinegar but as a rough guide try 3 parts JKW syrup to 1 part JKW vinegar. Add a splash of water. Too sweet, add a dash more vinegar. Too sour, add a dash more syrup.