With visions of beautifully presented, home made chutneys and relishes, I bought some Kilner preserving jars. I didn’t realise that when full, you put the (sterilised) disc and lid on and then boil them for 30 mins to create a vacuum. Do you really have to do that? It seems such a faff! Will the comtents keep without the vacuum?
It’s the high acid and sugar content of pickles and chutneys that preserve them. As they are cooked they will be mostly sterile by the time you pack them into jars, but not 100%. In most of western Europe the ambient temperature is low enough most of the year that the risk of surviving microorganisms starting to ferment in the jars is quite low.
American preservers, on the other hand, have to cope with a wider range of ambient temperatures, so will typically boil things after packing to pasteurize them as well. Practices that are OK for a larder in Sussex are not necessarily OK in the Nevada desert.