Chapter 25 begins with an omniscient third person description of California's land and productivity. The sentences are long, and the diction is formal and poetic, almost biblical, as Steinbeck describes the beauty of the fruit plants and the hard work that goes into growing them.
In the sixth paragraph, the chapter shifts abruptly into a gruff, first person voice, presumably the voice of a farmer: "Cent and a half a pound. Hell, we can't pick 'em for that." Now the descriptions show fruit dropping from trees and rotting on the ground as farmers grapple with the economic impossibility of profiting from the food they produce. A farmer makes rotting fruit into bad wine, saying cynically, "Oh, well. It has alcohol in it, anyway. They can get drunk."
From there, the chapter shifts back to an omniscient narrator and sweeping descriptions, but the tone is much darker. Now the narrator speaks of "great sorrow" as poor people die of malnutrition while crops rot. These rotting crops are directly compared to the anger that is beginning to fester in the hungry: "In the souls of the people the grapes of wrath are filling and growing heavy."