
Rhubarb liqueur is a liqueur built on the tart, vegetal character of rhubarb stalks.
Homemade blend
Mix two parts rhubarb syrup, three parts vodka, and one part water. You get the strength and sweetness of most liqueurs.
Swap it one for one. It keeps the tartness and sweetness, but will taste of apple instead of rhubarb.
A third of the original measure matches the sweetness, but the alcohol-free syrup adds no strength.
Rhubarb is a vegetable used as a fruit, and the liqueur is tarter than most fruit liqueurs. The sharpness comes from malic and oxalic acid in the stalks. Only the stalks are used; the leaves are toxic. The green, stalky note under the tartness is what other tart liqueurs lack, and the reason to keep a bottle.