This Thanksgiving, Be Grateful for Cranberries and Their Pectin

The cranberry is a unique little berry. 

First off, the fruit likes to grow in bogs, where the soil is acidic, nutrient-poor, and waterlogged. It is also unique in how it’s harvested: Cranberries are picked by hand, but the vast majority are harvested by flooding. 

But the coolest trait of the cranberry? Its high pectin content.

Pectin is cranberries’ superpower, allowing them to make thick and/or jellied sauces. However, these molecules can be pretty confusing. Some fruits have lots of pectin while other fruits are deficient, and the amount of pectin in a particular fruit changes based on ripeness. You can buy pectin at the store, but even that isn’t straightforward, with labels like “high methoxyl” and “low methoxyl” just making everything even more complicated.

In some ways it makes sense that pectin isn’t straightforward, since pectins are some of the most complex biological molecules that exist. But here’s how they work. 

Pectin comprises the walls of plant cells as well as the layer between the cells that holds them together. 

When pectins dissolve in water—for example, if you cook cranberries in liquid on the stovetop—their charged areas are drawn to each other, so they form a gel that holds water. But only when conditions are right. 

Low pH increases their ability to bond. And sugar facilitates the gelling by sequestering water. 

As for pH, pectin’s ideal range for gelling is pretty low: about 2.8-3.5. (For reference, lemon juice sits between 2 and 3 on the scale.)

And (according to Harold McGee in On Food and Cooking) pectin gels best when the sugar concentration falls between 60 and 65 percent. 

So, if you’re making jam with a high pectin fruit (or added pectin) with the right pH and the right amount of sugar, chances are good you’ll end up with a lovely set texture. 

To see what happens when you mess with sugar amounts, I ran the experiment below. 

Now there is a way to gel liquids from a wider range of sugar concentrations: adding calcium. Calcium ions help pectin molecules link, so they form a superstrong gel that traps water. Low-sugar—also known as low methoxyl—pectins at the store contain calcium. When I ran that same experiment using low-sugar pectin, I got gels starting at 42 percent and going all the way up to 79 percent.

Cranberry sauce is great, but in my mind it’s not the highest expression of the cranberry. That title goes to my colleague Lan Lam’s Cranberry Curd Tart. Here’s how you make it.

An added perk of pectin? Because that cranberry curd sets up so nicely, we can use those reserved two tablespoons to stabilize the whipped cream we are going to pipe over it. 

Calcium is pectin's friend: The calcium ions in the cream help the pectin molecules in the curd link, so they form a superstrong gel that traps both water and air. The upshot is a whipped cream topping so stable that it can be piped onto the tart hours before serving.

Ready to impress all your friends and family with your pectin knowledge? Get the full recipe for our jellied cranberry sauce and Lan’s cranberry curd tart below—and watch the latest episode of What’s Eating Dan? to learn even more about cranberries.