Seediness in raspberry jam is a topic of much discussion in canning circles. Without seeds, the yield is lower, the texture smooth and satiny. With all the seeds, the texture can be annoying and crunchy. Putting half the mixture through a food mill results in preserves full of flavor with just enough seeds to remember what it is you’re enjoying. If your preference runs to seedless jam, the food mill is your friend.
- Gently but thoroughly stir berries together with sugar and lemon juice in a large glass or ceramic bowl. Cover and refrigerate for 3 to 4 hours. Transfer berry mixture to a colander set over a preserving pot and allow syrup to drip into pot for 10 minutes or so. Remove colander from preserving pot and place in a bowl to capture any additional syrup. Clip a candy thermometer onto the pot, set over high heat, and bring syrup to 220 degrees, about 10 minutes. Remove pot from heat.
- Place a food mill over pot and mill half the berries into the syrup. Stir in remaining berries and bring to a boil over high heat. Stir continuously—this jam burns very easily. When foam has cleared, anywhere from 12 to 20 minutes depending on the fruit’s water content, remove from heat and cool for 3 minutes.
- Push against surface of jam. It should have set up a bit, resisting slightly and wrinkling at the surface. If preserves aren’t yet gelled to your satisfaction, turn heat on again for no more than 3 minutes, then turn it off and test again. When jam is ready, stir in butter to disperse any remaining foam and clarify the gel.
- Ladle into warm, prepared jars, leaving ½ inch of headspace. Process in a boiling water bath for 10 minutes.