Beser refers to an unripe or sour grape — fruit that has not yet matured and is inedible or bitter to the taste. The word carries connotations of premature development and unfulfilled potential. Unripe grapes were useless for wine and unpleasant to eat, making them a fitting metaphor for incomplete or premature action.
The unripe grape figures prominently in a proverb that both Jeremiah and Ezekiel quote and then challenge: "The fathers have eaten beser, and the children's teeth are set on edge" (Jeremiah 31:29; Ezekiel 18:2). This proverb expressed the fatalistic belief that children inevitably suffer for their parents' sins. Both prophets counter this with the announcement of personal accountability under the new covenant. The beser proverb will no longer apply — each person will bear their own responsibility before God. Job also uses the image to describe the wicked being shaken off like unripe grapes (Job 15:33).