Can i sterilise my filled jars of marmalade, raspberry and cherry jam in a steamer unit, such as those used to steam vegetables or baby bottles? I usually make batches of 15 jars so its difficult for me to double boil them all.
The key issue is getting the contents of each jar up to the requisite temperature for the necessary time, all the way through to the center of the jars. It would be conceivably possible to use steaming to do so, if the requisite controlled temperatures and times could be regulated, and appropriate recipes developed.
However, according to the USDA as reported at the National Center for Food Preservation:
If purpose built steam canners are not recommended, I would strongly urge you not to improvise with other devices.
You should only use recipes and methods for canning that come from highly reputable sources, such as a University Extension.