||fresh or good-quality frozen raspberries
In a medium saucepan, simmer the raspberries in the water until the juice has leached from the fruit and the water and berries are approximately the same color, 5 to 10 minutes. Strain through a strainer, pressing on the berries and then discarding them. Filter the juice through a coffee filter to clarify. While still hot, add the sugar, stirring until dissolved. Let cool, then bottle and refrigerate. The syrup will last about 3 weeks.
— Jeffrey Morgenthaler, The Bar Book