When does change happen?

The two women would 'put up' the preserves over a couple of days and invariably Marthe would ask, 'When does a cucumber become a pickle?'

At first he'd tried to answer that question as though she genuinely wanted to know. But over the years he realised there was no answer. At what point does change happen?

Louise Penny, Still Life (New York: St. Martin's Press, 2005), p.184