To contrast with Lisa's approach, I never follow any recipe at all.
When I started I had too much bad luck with recipes and found my
instinct worked better. One thing I would agree however is a recipe
can never be doubled, unless you double the surface area you are
cooking it down on. I usually cover the whole stove with big frying
pans so I can cook down the jam in a thin layer. I use the technique
of putting large spoons in the freezer before starting; jam dropped on
a frozen spoon quickly sets so you can get immediate feedback. That
feedback is critical for me. I also adjust the sugar amount during
the cook; I like to have as little sugar as possible, but if the set
is progressing slowly or the taste is not sweet enough I add more
sugar. If it is going super slow I will add commercial pectin toward
the end as well.
I made some jam from Indian Cling peaches last weekend. These peaches
had relatively little sugar in them so I added more than I usually do,
but they were loaded with pectin and the set was very fast. I had
never made peach jam from Indian Cling before and it was quite
different from other peaches so it would be hard to have a single
recipe work for both Indian Cling as well as regular type peaches.
The jam ended up coming out very chunky, more like chutney than your
normal jam. I would say these are better pie or tart peaches given
how well they hold their shape, but I still do like the chunky jam.
Scott
[NAFEX] making jams and jellies,
Scott Smith, 09/04/2008