Maraschino cherry syrup, as a mixed-in ingredient rather than a garnish, is a cherry-forward syrup built by simmering real cherries (brandied or good-quality maraschino, not the fluorescent-red supermarket jar) down with their own liquid and a little sugar and lemon. It's a different thing from Cherry Heering or a cherry liqueur — no added alcohol, closer in role to grenadine than to a cordial.
Real Cherries, Not the Neon Jar
Supermarket maraschino cherries are packed in a corn-syrup brine dyed with red food coloring — fine for topping a sundae, flat and one-note as a mixing syrup. Luxardo or a similar brandied cherry, packed in a syrup that's actually made from cherry juice, is the difference between a syrup that tastes like cherry and one that tastes like red sugar.
The Build
Real cherries and their packing syrup simmer briefly with a little extra sugar and a splash of lemon juice to keep the sweetness from turning flat, then get strained to a smooth syrup.
Storage and Shelf Life
About three weeks refrigerated in a clean jar — the sugar content of the cherries' own syrup helps it keep, but fresh lemon juice shortens the window slightly compared to a pure sugar syrup.
Bottom Line
A small-batch syrup worth making only when a recipe leans on cherry as a real flavor rather than a garnish afterthought — the Shark's Tooth is exactly that kind of drink.