Acidity and fig jam

Most fruits used for jam are acidic enough that pectin sets readily and that a boiling-water canning process is safe. Figs are an exception: they are a low-acid fruit. Tested home-canning recipes for figs therefore require added acid, usually bottled lemon juice or citric acid, before processing.¹

Flavour

A squeeze of lemon lifts a fig jam from sweet and flat to sweet and bright. Even in a jam you plan to keep in the refrigerator, it is worth adding for taste alone.

Set

Pectin needs acid to gel. Adding lemon juice improves the set of a no-added-pectin fig jam noticeably.

Safety

This is the part that is not negotiable. If you process fig jam or fig preserves in a boiling-water canner for shelf storage, follow a tested recipe and add the acid it specifies, in the amount and form it specifies. Bottled lemon juice is used in tested recipes because its acidity is standardised, unlike fresh lemons. See Food safety for the sources we rely on.