Try this Marilla's raspberry cordial recipe, or contribute your own.
Bringing the strained syrup and water to a rolling boil for exactly sixty seconds is the single operational step that dictates shelf stability and concentration. Watch the surface bubbles closely; they must transition from large, lazy foam bursts to a rapid, uniform agitation before you start timing. Removing the pot too early leaves excess moisture that promotes microbial growth, while exceeding the minute risks scorching the high volume of dissolved sugar.
Crushing the raspberries thoroughly while cold releases cellular pectin, which aids in body despite the subsequent straining through a colander. Mashing the fruit against the mesh until only dry seeds and fibrous pulp remain ensures a clear, vibrant concentrate. If you substitute bottled lemon juice for the white vinegar at a one-to-one ratio, expect a slight change in the final tartness profile due to varying acid levels.
Allowing the finished cordial to cool completely before transferring it to the refrigerator prevents condensation inside the storage container. Glass jugs work best for containment because plastic can absorb the persistent aromatic compounds of the berries. When serving, standard dilution ratios range from one part cordial to four parts chilled soda water, though personal preference ultimately guides the pour.