Name: Diane P.
How does a cucumber turn into a pickle? Is it due to
osmosis (which would explain why the water leaves the cucumber in a brine
solution and becomes shriveled)? If so, what happens to the semipermeable
membrane of the cucumber after the "shriveling" (osmotic forces); is it
altered to then allow the passage of salt molecules back into the
cucumber for the flavor, which would be diffusion?
I am interested in identifying the processes by which a cucumber is made
into a pickle!
You're correct that the salty brine used in the pickling process would cause
the cucumber to lose water through osmosis. The cell membranes do not
require alteration to allow for the passage of either water or salt
molecules. The primary event would be the movement of water out of the
cucumber to compensate for the osmotic differential. Then, the passive
transfer of salts across the cell membranes from the brine would also still
occur, but by diffusion or facilitated diffusion, as you suggest, which
occurs at a slower rate. This cellular response is actually an another
mechanism for equalizing intracellular osmotic pressure in hypertonic
environments. As for the cell membranes themselves, they are not really
harmed much by the osmotic "shriveling". Note how plant leaves that lose
their turgor and shrivel in dry conditions can recover once water is
as long as the dry period is not long enough to cause permanent cellular
damage. Cell membranes can rupture if too much water enters a cell by
osmosis, but plant cells are actually somewhat protected against that
problem by their rigid cell walls. The cell walls might also help prevent
severe damage during hypertonic membrane shrinkage, as well, by providing
some degree of structural support.
Thanks very much for the interesting question,
Jeff Buzby, Ph.D.
This is more complex than one might think but there are two main processes I
would consider involved: the preservation by the acetic acid (vinegar) which
will invade the cucumber by diffusion and the preservation by the
salt..which will invade the cucumber by diffusion. Initially there will be
some osmosis going on leading to a large loss of water from the cuke but
since the cuke is at least 80% water and there is no where near that amount
of loss in total cuke weight the water is replaced by the vinegar/brine
solution which preserves (pickles) the cuke.
Peter Faletra Ph.D.
Office of Science
Department of Energy
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Update: June 2012