Too little acid and it never sets, too much and it weeps
Updated
The two failures
Acid has a narrow band and both edges of it fail visibly. Too little and the pectin never forms a network; too much and the network forms and then contracts, squeezing liquid out. They look like different problems and they are the same variable in opposite directions.
| Acid | What happens | When you find out |
|---|---|---|
| Too little | The gel never forms | Within a day of filling |
| Too much | The gel forms, then releases liquid | Weeks later, in the jar |
The asymmetry is the useful part. Under-acid is a problem you discover and can sometimes fix; over-acid is a problem your customer discovers.
Where the acid comes from
Fruit brings its own and it varies more than people expect, with ripeness as much as with variety. That variation is why added acid exists and why the amount is not fixed across a season.
Some from the fruit, and how much depends on the fruit and on how ripe it is. The rest from added lemon juice, which is why the USDA ingredient tables list it per fruit in tablespoons rather than leaving it to taste. A recipe that specifies lemon juice is specifying acid, not brightness.
Weeping is the one to recognize
A weeping jar is the easier of the two to diagnose because it is unmistakable on a shelf, and it is also the one most often blamed on the wrong cause. Liquid standing on top of a set jar is read as a seal problem and is usually an acid one.
A jar that was fine and is now sitting in a pool of syrup is the over-acid failure, and extension guidance lists excess acid alongside warm or fluctuating storage as its two causes. Both are covered on it is weeping liquid in the jar.