There are bubbles in the jar
Updated
The two
Bubbles in a finished jar are either trapped air or something growing, and those two possibilities could not be further apart in what they mean. The useful skill is telling them apart quickly, because one is cosmetic and the other means the jar does not get sold.
| What you see | What it is | What to do |
|---|---|---|
| Still bubbles, set in the gel | Air trapped at the fill | Cosmetic |
| Bubbles moving | May denote spoilage | Do not use it |
The cosmetic case
Most bubbles are this one, and it is worth knowing what causes it so you can reduce it rather than live with it. It is a filling problem, not a recipe problem, which is good news because filling is easy to change.
A jar with air trapped in the body of the set is neither unsafe nor wrong, but it reads as careless on a shelf beside a jar that is clear. That is reason enough to fix it, and the fix costs nothing but a slower pour and a moment with a bubble tool before the lid goes on.
Trapped air comes from pouring too fast, from a gel that was starting to set in the pot, or from foam that was not skimmed. All three are fill-stage problems and they are on skimming the foam and filling hot.
Why the warning is worth repeating
The other case is rare and the consequence is serious enough that the published guidance repeats it rather than mentioning it once. It is repeated here for the same reason.
Because a jar of jam with bubbles in it looks like a cosmetic fault, and one of the two things it can be is not. Movement is the discriminator and it takes a second to check.