Turning fresh fruit into jams and jellies is a nearly magical process. Apples, quinces, citrus fruits and various berries all have the ability to set into a thick, spreadable gel after they're simply simmered with sugar. Other fruits require a little help -- in the form of added pectin. Commercial pectin comes in two main forms: liquid in a bottle or dry pectin powder in pouches. They do the same job, but are used differently.
Pectin is a sugar-like carbohydrate that occurs naturally in the cell walls of fruits and vegetables. Commercial pectin products are made by simmering high-pectin fruits such as apples and citrus, which are inexpensive and readily available, to extract those carbohydrates. You can make your own pectin by boiling citrus peels or under-ripe green apples, and then cooking down the juice to concentrate it. This, essentially, is the same thing as commercial liquid pectin. Dry pectin is made by evaporating the remaining water from liquid pectin to make a concentrated powder.
What It Does
Pectin, starch thickeners and even gelatin all work in much the same way. At the microscopic level, they create a fine three-dimensional mesh that traps water molecules in much the same way as a sponge. Pectin gels form best in an acidic environment; hence, recipes often call for lemon juice with relatively little or no added water. And it's why pectin-based jams often include large amounts of sugar. Sugar binds up a high percentage of the available water molecules, so pectin molecules bond with each other instead of the water.
Preserving aficionados are deeply divided on the subject of pectin. Some feel that it's unnecessary, since most fruits will eventually thicken if cooked down long enough. Others object to quantities of sugar needed in pectin recipes. Some also feel that adding pectin creates a too-firm gel, reminiscent of commercial jams.
On the other hand, adding pectin means you don't have to cook your fruit nearly as long, preserving much of its fresh flavor. It also allows for more jam or jelly from a given quantity of fruit, which is especially helpful when you're working with small quantities. Ultimately, it's a matter of personal preference.
Using Dry Pectin
Dry pectins vary somewhat in usage, depending on how they're formulated. Most varieties call for stirring the powder into the fruit as it cooks, so it can dissolve and disperse. Once you add the sugar to the recipe, your jam or jelly will set very rapidly. Individual brands might call for a different method, so work from the manufacturer's instructions whenever possible.
If you're using dry pectin in place of liquid pectin, the substitution is 4 teaspoons powder for every 2 tablespoons -- or 1 fluid ounce -- of liquid.