Fermenting jam

Occasionally a jar of jam will ferment in storage. The main causes are:

Jars that were not sterilised properly;

Fruit picked whilst it was wet;

Undercooking the jam so bacteria were not destroyed.

Jam that has been open for a while may also begin to ferment due to yeasts and bacteria in the air.

Generally you should not eat fermenting jam, although some jams can be intentionally fermented to produce a slightly tangy flavour. If you didn't intend to ferment the jam, or it smells odd or gassy, do NOT eat it - discard it.