Falernum is a Barbadian invention — a low-proof cordial built by infusing rum with lime zest, fresh ginger, cloves, and almond, then sweetening and souring the infusion into something between a liqueur and a spiced syrup. The commercial standard-bearer, John D. Taylor's Velvet Falernum, has been sold out of Barbados since the early 20th century; it and its imitators are what gives a Zombie, a Nuclear Daiquiri, or a Corn 'n Oil their particular clove-and-lime warmth.
Falernum Versus the Bottle
Velvet Falernum and its competitors (Fee Brothers, B.G. Reynolds) are real, decent products — nobody needs to apologize for keeping one on the shelf. But commercial falernum is built to a shelf-stable, crowd-pleasing spec, which usually means less ginger heat and less lime brightness than a fresh batch carries. A homemade falernum is punchier and shorter-lived — closer to a bar's own infusion than a supermarket cordial.
The Build
Falernum is an infusion, not a cooked syrup: white rum steeps with lime zest, crushed ginger, and whole cloves for a few days, then gets strained and cut with simple syrup and fresh lime juice to bring the proof and sweetness down to cordial range.
Zest, Not Juice
The lime goes in as zest — peeled with a vegetable peeler, pith avoided — because the citrus oil in the peel is what the rum extracts. The juice is added later, at the end, for acidity; infusing with juice instead of zest gives a flatter, less aromatic falernum.
Ginger and Clove, in Proportion
Ginger should be assertive but not the whole story — bruised or roughly chopped fresh ginger, not powder. Cloves are the easiest ingredient to overdo: a few whole cloves are plenty, and doubling them turns the batch medicinal rather than spiced.
Storage and Shelf Life
Strained and bottled, falernum keeps about a month refrigerated — longer than a fruit syrup since the rum base and sugar both help preserve it, but it will fade in brightness well before it spoils. Taste it every couple of weeks and use it while the ginger still has some heat.
Bottom Line
Falernum is one of the few tiki components worth infusing rather than just buying — the fresh-ginger heat doesn't survive bottling well, and it's the ingredient most likely to separate a good Zombie from a great one.