On Sun, 8 Sep 2013 12:50:17 +0100 (BST), Nick Maclaren wrote:

Somewhere in this house, I have a Ministry of Food booklet from the
1940s which describes the preservation of garden produce ("Dig For
Victory" and all that). It describes the bottling of fruit, and
says that bottling vegetables at home should not be attempted, as
it needs to be done under pressure.

Were domestic pressure cookers easily available during the war? I
have a feeling that they may have existed before but like a lot of
things disappeared during and only reappeared in the early 50's.

I agree there has been some mis-information in this thread,
bottling/canning really combines several preservation processes
depending on what is being bottled/canned. Broadly these processes
are heat treatment, hermetic sealing and sugar/acidity level.

The heat treatment and sugar acid levels are interrelated in that if
you have high sugar (jams etc) or high acid level (ph4.6 according
to wikipedia) you don't need to have heat treatment above 100C. If
the sugar content is low / acidity ph4.6 then you ought to have
high temperature treatment and the way to do that is in a pressure
vessel of some sort.

Trying to use the food type to define the bottling process required
can lead to an incorrect process being used.

--
Cheers
Dave.