This is a commonly used figurative English expression. The expression can be found both as “to take with a pinch of salt” and “to take with a grain of salt.” The latter is more commonly heard in the United States whilst the former is the norm in the British context.
The expression is used to denote the idea of taking a statement or story with a high degree of caution. It suggests that whilst one should accept the statement it is perhaps not fully true and thus there is a degree of scepticism present.
It is widely accepted that the idea behind the idiom comes from the fact that adding salt to food makes it easier to swallow. Therefore taking a statement with a pinch of salt will dilute or lessen any negative or harmful effects which it may have.
The expression “a grain of salt” can be dated back to 1647 in John Trapp’s Commentary on the Old and New Testaments which reads “this is to be taken with a grain of salt.” The version more commonly used in Britain is much more modern and the first recorded usage dates to the year 1948 in F. R. Cowell’s Cicero & the Roman Republic. The quote reads “amore critical spirit slowly developed, so that Cicero and his friends took more than the proverbial pinch of salt before swallowing everything written by these earlier authors.”
An example of this expression can be found in a quote from American musician Stefano Langone. The citation reads “the first thing you have to do is take everything with a grain of salt. You know, you’ve gotta just look at the goal, focus on what you gotta do and take one step at a time as a whole, as every performance being that’s it, that’s one objective, and let’s just move forward and work on that.”