Bob Hobden wrote:
Tony wrote
You've answered your own question on why salt.
Yes the salt does remove water from the onions by osmosis and therefore
softens them. This concentrates the liguid in the onion cells so that
the vinegar can add water again by osmosis, thereby resulting in
crunchy onions.

Why bother then, just do it my way and leave the original liquid in place.
Even crunchier onions.
Peel, pop in the jar, add spice and vinegar, seal and leave for 3 months
min.

Salt will hasten the process which is why it's used by professionals to
reduce stock within the process and save money tied up but I can't see any
advantage for amateur growers/picklers.

The amount of salt left on the onions is surely
dependant upon how thoroughly they are washed.

Some will dissolve in the onion juice and penetrate the onions, it will not
be washed off.

I might add we have just opened another jar of our pickled shallots, Jermor
this time and a year old now, and they are superb. When we have left them
two years they have still been crisp.
--
Regards
Bob
In Runnymede, 17 miles West of London
OK Bob
Here are the principles of osmosis, as I understand them from my O
level biology many many years ago.
When two aqueous solutions are separated from each other by a
semi-permeable membrane, the water in the dilute solution will always
diffuse more quickly through the membrane from the dilute solution to
the concentrated solution resulting in an equalisation of
concentrations.
The effectiveness of salting therefore depends upon one basic premise
i.e. that the concentration if the solution in the cells of the onion
or shallot is more dilute than that on the acetic acid solution in the
vinegar. This is highly likely because the solutions in cells are
usually very dilute because most chemical reactions in living organisms
occur more readily in dilute solutions.
Note that the diffusion is of water only, not salt, as the cell walls
are semi-permeable i.e. they only allow small molecules through.
Therefor when you add the salt, the solutions in the cell are
concentrated by losing water to the salt. Then when you add the vinegar
the water is returned to the cells because the vinegar is now more
dilute than the solutions in the cells.
It is likely that the salt also acts as a bactericide and fungicide
again by removing water from these other living organisms. Finally when
the vinegar loses water to the onion cells it becomes more concentrated
so that its preserving properties are enhanced. Salt can only enter the
cells where the cell walls are damaged for instance during peeling and
since salt is very soluble in water, it is readily washed off. If your
onions are nice and firm without salting then that must mean that your
vinegar is fairly dilute in which case I would doubt its preserving
properties. Every cookery book and preserving book that I have read
advocates salting most vegetables which when you understand the science
behind it is pretty clear.
Tony Bull
www.caterpillarfountain.co.uk