On 08/09/13 12:50, 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.

As supporting evidence for that...

"Home Preservation of Fruit and Vegetables" by Fish.& Food,Min.of
Agriculture (Jul 1989) isbn 0112428649, first published in 1929

That's an intensely practical book, also giving enough
theory to enable the reader to understand why the practice
has evolved.

It has chapters on jams, jellies, marmalade, fruit cheeses &
butters, mincemeat & other fruit preserves, bottled fruit,
fruit syrups and squashes, vinegars, pickles, chutneys,
ketchup, drying & salting, freezing, storing fruit & vegetables.

(1) botulism is mentioned prominently, with appropriate warnings
(2) some jams, e.g. cherry have added citric/tartaric acid
(3) all the methods for vegetables are freezing or drying or
adding to chutney and marrow jam requires extra acid
(4) THERE ARE NO RECIPES FOR CANNING/BOTTLING VEGETABLES unless
acid or salt are present
(5) pressure cooking: 5lb for bottled fruit, 10lb for jam,
15lb for nothing
(6) despite the book's title, there is relatively little
vegetables - just freeze them or dry them