Q: I followed a recipe for raspberry cordial that called for heating and straining raspberries, boiling the juice with sugar and mixing it with brandy. The next day, it had gelled, like a meat stock made with a bone. What made it gel?
Sounds as if you encountered a heteropolysaccharide - a big word for a helpful plant material called pectin.
Pectin occurs naturally in most fruits. If you're ever made jam with a powdered product called Sure-Gel, that's pectin.
Most fruits have some level of pectin, from low to high. Apples are among the highest. In fact, powdered pectin often is extracted from apples. Strawberries are low in it, which is why you usually have to add pectin to make jam.
Raspberries qualify as "medium" on the pectin scale. The high amount of sugar in the cordial recipe (8 ounces of sugar to 16 ounces of juice) also would have made the mixture seem thick when it was cooled. Combined with the pectin from the raspberries, it was probably enough to give a gelatinized consistency.
By the way, the substance that causes your meat stock to gel is collagen, not pectin. But that's a discussion for another column.
Kathleen Purvis answers cooking questions at www.charlotteobserver.com/food.