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What’s Wrong with My Jam?

With the strawberry season reaching its end and those fresh berries only lasting two to three days in the refrigerator, making jam is one way to enjoy strawberries all year round. Jams, jellies, preserves, conserves, and marmalades all contain the same four ingredients, sugar, pectin, acid, and fruit. Jam is made from ground or crushed fruit, jammed together to create a thick consistency. Whether you’ve canned jam a million times or a jam-making amateur, things occasionally go wrong. Proper food preparation and canning are essential to make not only the best jam but also the safest for the whole family to enjoy.

Notice the strawberries floating to the top of jars after processing? Fruit floating to the top is perfectly safe, and is due to a density difference between the liquid and fruit pieces. To prevent the separation use ripe fruit, and crush the berries into small pieces. Make sure to not overcook the fruit. Stir on and off for five minutes before putting the jam into jars, and make sure to follow the recipe exactly.

If jam comes out too stiff, it is often caused by overcooking fruit or the fruit spread having too much pectin. Pectin is naturally found in fruit and creates the gel and thickens jams and jellies. Many fruits, like apples and citrus peel, are high in pectin, while blueberries, cherries, and strawberries may require pectin to be added to thicken spreads. Additionally, overripe fruit is lower in pectin and can affect how jams and jellies set.

Jam that comes out too soft can be caused by undercooking fruit, moving the jar too quickly after processing, incorrect measurement of sugar, making too much at once, or not using enough acid. Jam should sit at least 12 hours after processing to allow time to set up. Another reason why jam might be soft is due to not waiting long before using it. Some jams and jellies can take up to two weeks to completely set.

Other than an undesirable consistency of jam, another common mishap is the formation of sugar crystals in jam. Crystals are caused by excess sugar, undissolved sugar sticking to the side of the pot when cooking, or cooking too slowly or too long. The exact measurement is critical in making jam, as well as making sure all of the sugar is dissolved before ladling into jars. Jam with crystals is still safe to eat.

Occasionally, air bubbles may appear when making jam. When pouring the jam into jars, pour quickly and use a bubble freer or a plastic knife around the inside edge of the jar. If the bubbles are moving inside the jar 24 hours after processing, this is a sign of spoilage, and jam should not be used.

Additional tips for canning include:

  • Sterilize canning jars for recipes requiring less than 10 minutes of processing.
  • Leave ¼ inch headspace at the top of the jar.
  • Always follow a scientifically tested recipe.

University of Illinois Nutrition and Wellness Extension team is offering weekly webinars every Wednesday, June through July, from 1-2 pm on preserving garden produce. On Wednesday, July 1, the focus is on canning jams and jellies. The class will go through the differences in jams, jellies, preserves, conserves, and marmalades, canning, the importance of pectin and sugar, how to remake jams and jellies as needed, and help troubleshoot issues. Call the extension office to sign up or register yourself at

Peach Jam  

Makes 6 half-pint jars

3 ¾ cups crushed peaches (about 3 lbs. peaches)

¼ cup lemon juice

1 package powdered pectin

5 cups sugar

1. Wash hands with soap and water. Sterilize canning jars and prepare two-piece canning lids according to manufacturer's instructions.

2. Sort and wash fully ripe peaches. Remove stems, skins, and pits—crush peaches.  

3. Measure crushed peaches into a kettle. Add lemon juice and pectin; stir well. Place on high heat and, stirring constantly, bring quickly to a full boil with bubbles over the entire surface. Add sugar, continue stirring, and heat again to a full bubbling boil. Boil hard for 1 minute, stirring constantly. Remove from heat; skim.

4. Fill hot jam immediately into hot, sterile jars, leaving ¼ inch headspace. Wipe rims of jars with a dampened clean paper towel; adjust two-piece metal canning lids—process in a boiling water canner for 5 minutes. Remove from canner and let jars sit undisturbed for 12-24 hours. Put any unsealed jars in the refrigerator. Store in a cool, dry place for one year for best quality.

Source: National Center for Home Food Preservation, 2005


Questions about food safety, nutrition, food preservation, or looking for recipes? Contact the local University of Illinois Extension office.

Source: Lisa Peterson, Extension Educator, Nutrition and Wellness