
Chocolate syrup is a thin, pourable syrup of cocoa and sugar in water, thickened with a gum and usually free of dairy.
With almost no fat, it disperses in a cold drink where a sauce would sink. It is denser than the other ingredients, so stir it into the base before the ice goes in. It also runs cleanly down the inside of a glass for a layered look.
Bottled chocolate syrup
Brands like Hershey's or Monin swap in straight.
Homemade chocolate syrup
Boil 45 g of cocoa powder, 400 g of sugar and 240 ml of water for 3 minutes while stirring. Let it cool, then add a few drops of vanilla if you want.
Crème de cacao
It brings alcohol and has about half the sugar. Use the same amount, taste, and add a little sugar syrup if needed.
Chocolate sauce
Won't work. It usually contains cream and often butter, making it too thick and fatty to mix into a cold glass.
A commercial bottle is stable for months and belongs in the fridge once opened. Homemade syrup has only its sugar to preserve it, so keep it two weeks chilled. Shake it before measuring, since the cocoa settles.