What Are the Functions of Pectin?

Homemade jams and jellies offer a range of flavors and colors you won't find at your local supermarket in mass-produced jars. When you make your own at home, you have near-total control over what the jam or jelly looks and tastes like, how thick it is, and what ingredients go into it. Those are all, to some degree, a function of pectin. Pectin is a natural gelling agent that's produced in fruits and vegetables, where it has functions above and beyond its role in preserves.

Food scientists define pectin as a polysaccharide, which is a five-dollar word that literally means "lots of sugars." Simple sugars themselves are small molecules, and your body can easily digest them. If you connect lots of sugars together in larger molecules, you get starches. Your body can still use those; it just has to break them back down into sugars first. When you pack lots of sugars together into even larger molecules, you get cellulose or — in food terms — dietary fiber. Your body can't digest that, but it's still important for your health in many ways.

Pectin is a very distinct form of polysaccharide called a hemicellulose, which means it's a bit more complex than a starch but not as rigid and indigestible as cellulose. The term hemicellulose itself is a scientific way of saying "almost cellulose, but not quite." Both pectins and cellulose occur in the cell walls of plants, where they have a good working partnership.

In humans and other vertebrates, our skeleton holds all of our organs in place and gives us the rigidity we need to stand up and walk around. Plants don't need to walk, but they do need some form of structure to help them grow, hold their leaves up to the sun and eventually reproduce. That structure comes from cellulose, which gives plant cells a degree of sturdiness and rigidity. Next, just as the human body has muscles, ligaments and cartilage to hold its bones together, plants need a way to hold those cellulose fibers together. That's where pectin comes in.

It's the pectin molecules that bind the cellulose fibers together and give the plant its rigidity. You could think of pectin molecules as mortar to the cell walls' bricks or – even better – picture pectin as the concrete and the cellulose fibers as the bars of steel reinforcing them. Whichever analogy you choose, it's that partnership between pectin and cellulose that determines the texture of a fruit or vegetable.

Think of the textures of the fruits and vegetables you've eaten over the past week. Some are relatively soft and delicate, while others are crunchy or even hard. That texture comes from the strength of the bonds between the cell walls, or — to say the same thing in a different way — between the pectins and cellulose. When you bite into a forkful of salad, your teeth sever the bonds between those cells by applying what's called shearing force. Crunchy fruits and vegetables require a lot of shearing force, but soft ones don't.

This doesn't necessarily mean that the hardest or crunchiest foods automatically have the most pectin. Carrots are crunchy but have relatively little pectin, while sweet peppers and citrus fruit have quite a lot. Within a single type of fruit, texture is a more reliable indicator. Firm, slightly underripe pears and apples have more pectin than their softer, fully matured counterparts, while quinces — a close relative — are rock-hard and especially high in pectin.

There are two kinds of fiber found in foods, the insoluble kind and the soluble. Insoluble fiber is the kind that used to be called "roughage." It's made up of cellulose, and it passes through the gut undigested. Pectins and other hemicelluloses are forms of soluble fiber, which means they dissolve in liquids. This kind of fiber shows up in foods like beans and oatmeal as well, and it's valued for the role it plays in keeping your blood sugars in check and maintaining heart health. For cooks, though, another important detail is that soluble fiber acts as a thickener.

Oatmeal is a pretty polarizing food, because some people love it for its flavor and health benefits while others hate it for its sticky, goopy texture. That texture comes from beta-glucans, a kind of hemicellulose that's found in oats. When the oats are cooked, the beta-glucans dissolve into the water and form a gel. Pectin does much the same thing in its way.

At the microscopic level, here's what happens. The pectin molecules open up as they're heated, and the outstretched ends of those molecules begin to bond together. Eventually, as they form ever-widening nets of molecules, they begin to trap water molecules between them. It's very much the same thing you see on a larger scale when you soak up a spill with a sponge or a paper towel: The water is just held in place, and it can't flow anymore. The end result is a soft gel, which holds its shape on a spoon or a knife but spreads easily on a piece of bread or toast.

The soluble fiber in oats is easy to work with. As long as you moisten and heat your oats, they'll become thick and sticky. Fruit pectin is a little more finicky to work with, because it requires a fairly specialized set of conditions before it can do its job. First, you need a certain amount of acidity. Recipes often call for added lemon juice if you're working with fruits that don't have a lot of acidity, and this is why. It also helps balance the sweetness of the sugar in your jam or jelly, but that's just a side benefit.

The acidity changes the electrical charge of the pectin molecules, making it easier for them to bind together. The amount of water in your jam or jelly is an impediment, though. Picture trying to wade through a ball pit to grasp someone's hand, and you've got the basic idea. For pectin to form a gel, you've got to reduce the amount of available water, and there are two ways of doing that.

Some of the oldest jam recipes call for simply boiling down your fruit with as much sweetener as you need to make it taste good. As you boil the pot — stirring carefully to keep it from sticking and burning — eventually, you'll boil out enough water that the pectin molecules can begin bonding to each other and form a gel. This produces a very concentrated jam, but there are two obvious drawbacks to this method. One is that it makes a small amount of jam from a given weight of fruit, and the other is that it has a very "cooked" flavor.

A second option is just to add more sugar, which is why that's such a major ingredient in modern jam recipes. Sugar binds very easily to water molecules. Every water molecule bound up by the sugar is one that can't get in the way of the pectin, so it bonds with a lot less boiling. This makes for bigger batches from the same amount of fruit, and the jam will have a fresher taste. The downside, of course, is that you'll use and eat a lot more sugar.

Fruit pectin is more concentrated in some fruits and berries than others. Seedy berries, such as strawberries and raspberries, have a relatively high amount in their seeds. Citrus fruits contain quite a lot, but it's concentrated in their peels. That's why the peels are used to make marmalade. Apples have a lot of pectin, especially when they're still a bit green, and quinces have a tremendous amount. They're an old-fashioned fruit from the same family as apples, but they're too hard and tart to eat raw.

If you're making jam from high-pectin fruits or berries, you have the option of using less sugar and little-or-no-added commercial pectin. You can also make your jam from a blend of fruits, adding high-pectin apples or quinces to other fruits that don't have as much pectin of their own. In the days before commercial pectin was available from the store, farms often had a quince bush or two to provide pectin for jam-making.

If you'd like to experiment with making fruit pectin on your own, it's easy enough to do on the stovetop in a large soup pot. Fill the pot with coarsely chopped apples or quinces or sliced citrus-fruit peels, and add a few tablespoons of lemon juice and enough water to cover the fruit. Simmer citrus peels for 20 to 30 minutes, apples for about an hour, or quinces for two hours or longer as needed — they're really hard! — until the fruit is completely tender.

Strain the liquid from the fruit in a fine strainer or colander, and then simmer it again until the liquid is thick and sticky. Strain it once more through cheesecloth or a jelly bag, pour it into sterile Mason jars, and keep it refrigerated until you're ready to make jam or jelly.

If you'd rather just buy your pectin, it's available at most grocery stores year-round. It comes in two main forms, a liquid and a powder. They're much the same, so the one you choose is largely a matter of personal preference. The liquid kind can simply be stirred into your crushed fruit or strained juice, while the powdered kind must be dissolved first and then stirred through the fruit or juice. The powdered kind takes up less space in your pantry, though, which is a convenience.

The main role of pectin in jelly-making is to thicken the clear juice without making it cloudy, which would be an issue if you relied on adding high-pectin fruit or poorly filtered homemade pectin. You may notice that some kinds of store-bought pectin are also labeled as "rapid set" or "slow set." The slow set variety will give you the finest, clearest jellies. Rapid set doesn't give quite as crystalline a finish, but it's useful if you want to have other ingredients such as berries or strips of candied fruit suspended in the jelly when it's done.

There's one other form of pectin that's worth mentioning. Many brands also make a special variety of pectin for jam or jelly that doesn't require nearly as much sugar. It's usually labeled as "light" or low-sugar pectin, or low-methoxyl pectin — regular pectin is high-methoxyl — to food scientists. Low-methoxyl pectin doesn't form a gel in the presence of sugar and acidity; instead, it forms a gel in the presence of calcium. You'll find a small package of calcium powder inside the package along with your pectin, and you dissolve that and stir it into your jam or jelly to make it set.

You'll still need to use some sugar, but you won't have to use nearly as much. As long as you use the minimum called for in the recipe, you can let your taste buds "say when." In many cases, you can even use sugar-free sweeteners. Just be aware that sugar is a preservative, so sugar-free or low-sugar jams and jellies might not look as pretty or last as long as their conventional counterparts.