It came out darker than it should be
Updated
The causes, by product
Darkening has different causes in jam and in jelly, which is why a single explanation does not fit. Sorting by product first narrows it to two or three possibilities rather than six, and most of those are about heat and time rather than about the fruit.
| Product | Causes given |
|---|---|
| Jelly and jam | Overcooking the sugar and juice; stored too long or too warm |
| Preserves | Cooking too large a quantity at once; cooked too slowly; overcooked |
Why batch size appears again
Batch size turns up in almost every failure in this craft, and darkening is one of the clearest cases. A larger batch spends longer at heat to reach the same concentration, and color is one of the things that pays for that time.
It is on the soft-set list too, from the opposite direction. A pot too full takes too long to reach temperature, and the extra time on the heat is what darkens it. Batch size is the single variable that shows up in the most failure modes, which is why cooking it to the point it will set treats it as a constraint rather than a preference.
The storage half
Some darkening happens after the jar is sealed, which means it is a storage problem rather than a cooking one and the fix is in a different room. If a batch left the kitchen the right color and is darker two months later, nothing about the recipe needs changing and the store does.
Stored too long, or too warm. That makes color a shelf-life indicator as well as a cook indicator, and it is the reason a product that looked right leaving you can look wrong on arrival.