Fruits And The Science Of Pectin


Pectin is a carbohydrate found naturally in fruit, but it is also a commercially made product designed specifically for making jams. Pectin is a crucial element in jam because it provides structure. Without pectin, a jam wouldn’t set up into a spreadable texture but rather would have the consistency of a pourable fruit puree. Yet pectin is a somewhat mysterious element in jam, and most cooks have questions about how it works. Below are the most common pectin questions along with our straightforward and kitchen-vetted answers.

When Do I Need to Add Commercial Pectin?

All fresh fruit contains pectin, but some fruits contain more than others. Many jam recipes warn that low-pectin fruits require the addition of commercially made pectin in order for the jam set up, but we didn’t find this be true. In test after test, we found that jam made with low-pectin fruits didn’t require commercial pectin to set up, and in fact it often gave the jam an unappealing, rubbery texture.

This isn’t to say that we don’t use commercial pectin in any recipes in this book. To make jelly, we found it far more foolproof to use commercial pectin than to rely on the pectin in the juice. We also found it beneficial to add commercial pectin to a few other recipes, including Classic Blueberry Jam and Blueberry–Earl Grey Jam, Cherry Preserves, and Carrot Marmalade. We could get these recipes to set up without the commercial pectin, but it required cooking the blueberries, cherries, or carrots for longer than we wanted, which ruined their fresh flavors and textures. Before adding Commercial Pectin you may Read more about the wide world of salt.

How Do I Get the Pectin to Work?

Bowl of red raspberries on a table

No matter if you’re using commercial pectin or relying on the natural pectin from the fruit, you need to have three key factors—water, sugar, and pH—at the right temperature and in proper proportion before the pectin will do its thickening job. Otherwise, the pectin molecules will simply float around in the jam mixture and do nothing. When these factors fall into place, the pectin molecules bond to each other to form a web-like structure that holds the fruit and sugar in place, making the jam set. We’ve already lined up these three factors in our recipes so that the pectin will always set, but here’s how it all works.

The goal is to get the pectin molecules to bond to each other, yet the pectin would much rather bond to water molecules. This is where the sugar comes in. Sugar molecules form a stronger bond with the water and actively pull the water away from the pectin when added to the jam.

Even if the pectin molecules are free agents and not bonded with water, they won’t bond to each other because they are negatively charged. This is where the pH comes in. Making the jam slightly acidic (low pH) by adding lemon or lime juice neutralizes this negative charge and encourages the pectin molecules to bond to each other.

Lastly, the level of water in the jam needs to be reduced just enough so that all of the strands of linked pectin molecules can connect with each other to form a web. If there is too much water in the way, the pectin strands simply can’t close the distance in between.

How Do I Know That the Jam Has Set Up?

Close-up of colorful fruit on a table

If you’re using commercial pectin, you don’t have to test the jam’s set using any special tests. You just need to make sure that you’ve boiled the pectin in the jam for a minute or two after adding the sugar. Don’t overboil the pectin or it will lose its thickening power.

If relying on the natural pectin in the fruit, you’ll need to monitor the temperature of the jam as it cooks and run a set point test. Taking the temperature of the jam isn’t a foolproof way of knowing if it’s done, but it will let you know when you’re getting close. The ideal set point for a jam is roughly 8 degrees above the boiling point of water; click here for more information on the set point of jams at different elevations.

Our favorite method for determining if a jam has reached its set point is a frozen plate test. This simply involves putting a small amount of the hot jam on a chilled plate, chilling it in the freezer for 2 minutes, and then checking its texture. Essentially, it’s super chilling a small amount of the jam to see what it will look like when fully cooled. Get informed about safety criteria for each preservation system.

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