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We don't think the size ofWe don't think the size of your jars is the problem. Did you crush the strawberries before cooking? Chopped fruit can sometimes contain air, so you need to crush the fruit before cooking. Also, try gently stirring the jam every so often for 5 minutes after it is removed from the heat. We have even heard of people turning their jars upside down halfway through the gelling process, but sometimes this can affect the seal.

2015 Special Edition Garden GuideCooking Fresh with The Old Farmer's AlmanacThe Almanac Monthly Digital MagazineWhat the heck is a Garden Hod?