Read any recipe for jam, and eventually you will come to some variation of the following instructional step: “Skim the foam from the jam.”
What is foam? Why do we skim it? How do we skim it? Do we have to skim it at all? Is jam foam a safety issue? An appearance issue? What should we do with the foam once we skim it off? This article will attempt to corral and answer all yours questions about skimming foam when making jam.
What is jam foam?
The foam that rises from cooking jam is simply air bubbles, trapped in something like a jam matrix. It’s light, thick and spoonable, with very fine bubbles. If jam was akin to caramel sauce, jam foam would be more like cotton candy.
According to my friend, Master Food Preserver Theresa Loe:
The air content of the fruit itself causes foaming. Chopping, mashing and macerating the fruit in sugar overnight will result in less foam because you’re removing some of the air pockets from the fruit before you cook your jam. Pectin doesn’t seem to have an impact on foaming – strawberries (low in pectin) are notorious for foaming but cranberries (high in pectin) also generate lots of foam.
What’s wrong with foam from jam?
Jam foam has a different texture and color from your jam, jelly, or other fruit preserve. If you don’t remove it from your jam before processing, you won’t achieve the clear, jewel-like colors that are prized in jam making.