Can you explain the miracle Sai Baba performed with the grapes for Boss Dharamsee?

Certainly. The miracle of the grapes is a well-documented event from Chapter 35. A devotee named Kaka brought grapes with seeds as an offering to Baba. Baba began distributing them, and when he offered some to Boss Dharamsee, Dharamsee was hesitant because he disliked that variety and was concerned about eating them unwashed. He thought to himself that a true saint should know his preference. As this thought arose, Baba gave him even more grapes. When Baba insisted he eat them, Dharamsee put them in his mouth and was astonished to find they were completely seedless. This miracle demonstrated Baba's omniscience and his power to alter reality to foster faith in a devotee's heart.