The source's simple method uses 100 grams of sugar and 100 grams of still-hot brewed coffee. It suggests brewing the coffee more concentrated than an ordinary cup, around a one-to-ten coffee-to-water ratio, before taking the measured portion.
Stir the sugar into the hot coffee until dissolved. Unlike a long reduction, the aim is not to boil away water for an hour to create a very thick sauce. That distinction matters when a syrup is intended to mix readily into a drink instead of sitting on top of a dessert.
Choose the coffee's flavor direction according to its intended use and record the quantities. Different sweeteners can behave differently, so an equal-weight substitution deserves its own comparison. Use suitable handling and storage guidance for the prepared syrup rather than assuming every homemade version keeps indefinitely.
The conversation
A good question can make a better brew.