Sweetness defines jams—and sometimes overpowers them. To my mind, a jam that leaves a lingering coat of sugar on your tongue misses the point: savor the fruits of summer. Making fruit-forward jam is simple once you understand a bit of the science behind it.
Fruit needs three things to set, or thicken, a spreadable consistency: acid, sugar, and pectin. Think of the molecular interactions in fruit like a high-school romance: Pectin molecules are attracted to water, but water is attracted to sugar. If water and sugar “hook up,” the pectin molecules will bond—with a little encouragement from their best friend, acid—and the jam will thicken.
The traditional method of encouraging this interaction is to throw enough sugar into the batch to distract all the water molecules. But more sugar is not the only option. An acidic pectin, like one based on citrus fruits, is an effective matchmaker for pectin molecules. Another method to encourage pectin couplings is to reduce the pool of available water molecules.
Acid and sugar also play preservative roles. Acid lets you seal a jar of jam in a boiling water bath and leave it on a shelf at room temperature. Unlike vegetables, most fruits are naturally acidic and can’t lead to botulism. Sugar is a preservative because it pulls water from fruit, but it primarily slows spoilage once the jar is open. Jam with little or no added sugar can still be canned safely, but once opened, the jar won’t keep as long in the fridge.
Any-Fruit Jam without Added Pectin
1-1/2 tablespoons lemon or lime juice
1-1/2 to 3 cups sweetener
1–2 tablespoons fresh edible herbs or flowers to taste (optional)
Clean and prepare your fruit, ensuring it is free of dirt and inedible parts and slicing it as needed. Separate the pulp from the juice as for Fruit Syrups, either freezing and defrosting or macerating and roasting the fruit. Set the juice aside for a syrup or other use.
Mash the remaining fruit pulp, ensuring you have 6 cups, and add it to a wide, 6- to 8-quart pot. Add the citrus juice and bring the fruit to a boil, stirring constantly to prevent sticking. Add up to 3 cups of sweetener, depending on whether your fruit was sweetened before you removed the juice, and cook for 5–15 minutes, or until the mixture is thickens to your liking or hold its shape when a drop is placed on a chilled plate. Remove the pan from the heat and stir in fresh botanicals if desired.
Tips & Tricks
- By knowing a bit about the science behind and the ratios for processed jams, it’s easy to create your own custom blends. My favorites include apricot–raspberry, sour cherry–apple, and cranberry–pear.
- When I first started reading jam recipes, the additional citrus juice seemed unnecessary, because most fruits are naturally acidic enough that they can be processed safely. I didn’t find a clear explanation until I read about the science of pectin in Foolproof Preserving. Canning guru Linda Ziedrich recommends 1/2 tablespoon of lemon juice per pound of any fruit.
- If you macerate your fruit to separate the juice from the pulp, you’re adding sugar in stages: part during the maceration and the rest during the jam making. If you used a freeze–thaw technique, add all 3 cups of sugar to the separated fruit pulp.
- Creating fruit pulp drains away some of the water, leaving more pectin (making the jam gel more easily) and more fiber (giving it a natural thickness that makes gelling less important). I’ve found the plate test mentioned here to be sufficient for a soft-spread jam, but a thermometer is more exact; jam’s set point is about 8°F above the boiling point of water at your altitude. You’ll rarely need to test the set of jams with added pectin (see below).
- Adding edible herbs and flowers to your fruit boosts the gourmet factor. As with sorbets, the combinations are endless, but you only need 1–2 teaspoons of fresh herbs per pound of fruit to make an impression. If using dried herbs or spices, start with 1/3–2/3 teaspoon per pound of fruit.
- Flavorings left in processed jam will strengthen over time. To hold the flavor steady, tie the botanicals into a piece of cheesecloth or pack them into a tea strainer. Add this to the pot before you bring the fruit to a boil, and then remove it before you ladle the jam into jars.
Twice as Tasty
I always use Pomona’s Universal Pectin when I want extra gel in a spread. Unlike most other pectins, this brand is extracted from citrus peel and activated by calcium, with no additional ingredients in the box.
Citrus-based pectin has many advantages. Although the price per box may look higher, you can get about four batches from it instead of the usual one. You can also cook multiple batches at once, although the jam forms more consistently in single batches. It sets up with little or no sweetener, preserving a freshly picked fruit flavor.
I find the Pomona brand in natural food stores and some supermarkets in my area; you can always purchase it online if you can’t find a box locally. If you substitute standard pectin, follow that package’s directions; the jam may not set well with so little sweetener.
Any-Fruit Jam with Added Pectin
about 2-1/2 pounds fruit (6 cups when mashed)
3/4 to 1-1/2 cups sweetener
3 or 4-1/2 teaspoons Pomona’s pectin powder
6 tablespoons lemon or lime juice, or to taste for tart fruits
1–2 tablespoons fresh edible herbs or flowers to taste (optional)
Prepare the calcium water according the Pomona’s Universal Pectin package directions, combining the calcium powder with 1/2 cup of water and shaking. Clean and then chop or crush the fruit to your desired texture; ensure you have 6 cups, and add the fruit to a wide, 6- to 8-quart pot.
In a bowl, measure out the sweetener as desired. Sprinkle with 3 or 4-1/2 teaspoons pectin powder, using the lower quantity for tart fruits, like berries, and the higher quantity for sweet fruits, like peaches and pears. Mix in the powder completely.
Stir the calcium water and citrus juice into the fruit in the pot. Bring to a boil over high heat, and then add the sweetener and pectin mixture. Cook, stirring constantly, for 1–4 minutes, just until the pectin dissolves and the jam boils again. Remove the pot from the heat and stir in edible botanicals as desired.
Tips & Tricks
- This recipe is based on the ratios recommended in the Pomona’s packaging; I simply scaled it up to avoid a half-full canning kettle. For more info, read the detailed instructions within each box.
- You can store excess calcium water in the fridge for the jamming season to ensure you have some on hand if you spill or miscalculate. The powder may settle, so shake the jar just before each use.
- Fruit weight versus final volume can vary. For fruit with large pits or thick inedible peels, weigh out an extra 1/4–1/2 pound. Or do the math and adjust your batch your harvested weight.
- A little math also makes it easy to mix fruits. I create Tart Berry Jam using equal amounts of raspberries, blackberries, and blueberries. You can also mix tart and sweet flavors and add herbs and other flavorings as in pectin-free jam; just keep track of how many cups you use of each fruit type.
- If the fruit did not mash easily, bring it to a simmer with a bit of water to prevent sticking. Cook for about 5 minutes to soften, and then crush again with a potato masher.
- This type of pectin lets you choose the type and amount of sweetener to add. Unsweetened is an option, but the jam may gel less completely or last less than 3 weeks in the fridge. I prefer 3/4 cup of honey in a batch of Tart Berry Jam; bump that to 1 cup if using granulated sugar.
- Mixing pectin into sugar and then boiling it briefly is enough to set a jam. Overboiling has the opposite effect and weakens the pectin’s thickening power.
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