Thanks to the advice above, I emailed the appropriate authority in Australia regarding my jam. I received the following response:
Dear Xyzzy,
Thank you for your enquiry about bringing jam into Australia as part of
your personal baggage. The conditions for bringing jam into Australia as
part of your personal baggage are:
Jams and conserves are permitted entry into Australia as part of a
passenger's personal baggage but must be presented for inspection by an
AQIS officer upon arrival, to ensure that the jam or conserve is:
a) commercially prepared and packaged, or
b) boiled with sugar and pectin and the finished product is
sufficiently gelled in the container.
The product must be shelf stable, being a non-perishable food with a
shelf life of many months to years. If the product does not meet these
conditions, the item must be re-exported or destroyed. Costs for
re-export of the items must be paid for by the importer.
Unfortunately, the reply arrived 12 hours after I left home. So, I'll be bringing my jam on my next trip.