Canning Jam - Preventing Floating Fruit

Recently somebody asked me why the fruit in jam sometimes floats to the top, leaving only jelly at the bottom of the jar. At the time, the only answer that I could honestly give was, "I wish I knew the answer to that."

I just recently got a copy of 175 Best Jams, Jellies, Marmalades and Other Soft Spreads, by Linda J Amendt. It turns out that it had a section on the topic of, "Preventing floating fruit."


According to the author, the most common cause of floating fruit is fruit that was chopped rather than crushed. She says that chopped fruit contains air trapped in the cells, and it does not absorb sugar well. She reminds people to cut the fruit into small pieces and then gently crush them with a potato masher.

I have been guilty of just chopping fruit before. I have even seen recipes in cookbooks that just say to chop the fruit. This has usually been the times when my fruit ended up floating so it appears that that she knows what she is talking about. From now on, I will have to try modifying any recipe that calls for chopped fruit.

For making preserves (which have larger pieces of fruit than jam does) she says to cut the fruit up, mix it with some of the sugar, and then let it sit for a while before cooking it. She says this gives the fruit time to absorb sugar. Many of her recipes for preserves say to let it sit in sugar for 30 minutes, but some say to let it sit for 1 hour. The recipes seem to vary, based on the type of fruit.