The meaning of the title helps to understand the fighting Steinbeck
The title of the novel, The Grapes of Wrath, Graps of wrath in English, is from the American patriotic song The Battle Hymn of the Republic, sung by the Unionists (North of US soldiers). This song is both Republican and religious advocates since the abolition of slavery, the desire of the Lord. The second verse is: He is trampling out the vintage Where the graps of wrath are Stored (It tramples the vineyard where the grapes are kept of anger). It refers to the divine indignation wine described in the Apocalypse of St. John, with whom the angels of God be berthed Earth then dominated by the Beast.
This is in Chapter XXV Steinbeck explains its title. Because of the economic crisis and extremely low prices exerted on the fruit, no profit may not be made on crops of peaches, cherries, plums or grapes ... Except for the super-farms. Fruit rot or are destroyed by farmers, not wanting to help immigrants of Middle hungry West, on which they put the blame for this decline in prices. Seasonal starving, smallholders left to rot fruit: a climate of extreme tension arises ". In the soul of the people the grapes of wrath swell and ripen, announcing the next harvest"