Pectin, a water-soluble fiber, occurs naturally in most fruits, with the highest concentration in the peel or skin; it makes jellies gel, gives jams their spreadable consistency, and causes preserves to set. A polysaccharide or long-chain carbohydrate formed of sugar molecules, pectin molecules bind together in a network that traps liquid in sponge-like pockets, giving fruit preserves their structure. Fully ripe fruit, while generally sweeter and more delicious, contains less pectin than slightly under-ripe fruit, whether in the high-pectin or low-pectin category.
How Pectin Works
Fruits low in pectin usually need to pair with high-pectin fruits to get a good gel. You can also add commercial or homemade pectin to compensate for naturally low amounts or to speed the process.
Pectin, whether naturally occurring or added, requires heat, sugar, and acid to activate. Some acidic fruits with high levels of pectin such as lemons gel easily without much coercing. Low-acid, low-pectin fruits such as strawberries require some finessing to turn them into a spreadable confection. Lemon juice provides the necessary acid in many berry jam recipes, while a classic strawberry and red currant preserves recipe combine low- and high-pectin fruits (it helps that they are in season at the same time).
Working With Pectin
Classic jellies, jams, and preserves begin with fresh fruit, cooked until it breaks down into the consistency of a sauce. This process releases the pectin chains from the cell walls of the fruit, allowing them to dissolve in the liquidy mash. Bringing them back together requires added sugar, which absorbs some of the excess moisture, and an acid component, which neutralizes the negative electrical charge preventing the pectin molecules from automatically bonding again in the mash.
Follow the recipe closely when you add commercial pectin, which bonds much more quickly and strongly than natural pectin and can result in too much of a Jell-O consistency. Different recipes call for different forms of pectin, so read the instructions on the box carefully as well.
You can use some fruit juices instead of fresh fruit to make smooth jellies, but most juices contain less natural pectin than their fresh fruit counterpart, so you almost always need supplemental pectin, either a commercial variety or homemade. Pectin continues to gel as it cools, so you typically pull fruit preserves off of the stove at the point that they just coat the back of a spoon, running together into a single drop that falls off the end.
Adding pectin to fruit can eliminate the need for a lengthy boil, preserving more of the fresh flavor and texture. Simple freezer jam recipes mix smashed fresh fruit with sugar and concentrated pectin, then let them sit for a day or two while the pectin network forms and causes the fruit to gel.
- tart, underripe apples
- unripe blackberries
- lemons, limes
- crab apples
- plums (but not Italian variety)
- grapes (Eastern Concord variety)
- ripe apples
- ripe blackberries
- sour cherries
- grapes (California)
- ripe cherries
- Italian plums