RHUBARB

Rhubarb travelled to your glass the long way round. The plant is Asian — Rheum is native to China and Siberia, where the root was prized as "the great yellow," a medicine recorded in Chinese herbals nearly two thousand years ago. [source] Carried west along the Silk Road, dried medicinal root reached Europe by the 14th century through the ports of Aleppo and Smyrna as "Turkish rhubarb," later eclipsed by quality-controlled "Russian rhubarb." [source] Only much later did anyone eat the stalk: Scotland harvested it from at least 1786, England around 1820. [source] Its great theatre is the Yorkshire Rhubarb Triangle between Wakefield, Morley and Rothwell, where "forced" rhubarb is drawn up in pitch-dark heated sheds and pulled by candlelight — a craft awarded Protected Designation of Origin status in 2010. [source]

Rhubarb is a colour-and-tartness botanical rather than a juniper-style backbone. A full sachet, or fresh-pressed stalk juice, makes it the headline — that blush-pink, sour-sweet character behind every modern rhubarb gin. Used lightly it lifts a classic gin with a crisp, green-fruit tartness. Its natural partner is ginger, the pairing made famous by countless rhubarb-and-ginger gins; angelica and citrus peel sharpen it further.

Rhubarb's signature is acid, not oil. The stalk's tartness comes from a total acidity of about 2–2.5%, mostly malic acid, with oxalic acid at roughly 10% of that total giving the sharp, mouth-puckering edge, and citric acid adding a secondary brightness. [source] Those acids are water-soluble, so cold maceration or pressed juice carries the sourness and colour straight into the spirit. The green, "fresh-cut stalk" top-note is a trace of C6 aldehydes — chiefly (E)-2-hexenal — shown by gas chromatography-olfactometry to be sensory-key to rhubarb aroma; these are delicate, so keep heat low to hold that lift. [source] Pair with ginger to warm the sourness; with strawberry to round it.