Why is the book called grapes of wrath?

The title, The Grapes of Wrath, is pulled directly from "The Battle Hymn of the Republic." What the hey is this "Battle Hymn" you speak of? Well, even if you don't recognize this song's title, you will likely know the chorus and its melody like the back of your hand. It goes something like this:

Mine eyes have seen the glory of the coming of the Lord:

He is trampling out the vintage where the grapes of wrath are stored;

He hath loosed the fateful lightning of His terrible swift sword:

His truth is marching on.

(Chorus)

Glory, glory, hallelujah!

Glory, glory, hallelujah!

Glory, glory, hallelujah!

His truth is marching on.

"The Battle Hymn of the Republic" was written by abolitionist Julia Ward Howe in 1861, the night after she visited a Union army camp on the Potomac River near Washington D.C. The hymn became a kind of anthem for the abolitionist cause and for the Union soldiers during the Civil War in America. The hymn was published in the Atlantic Monthly in February, 1862. Since then, this song has been woven into the fabric of American culture, appearing in books, movies, speeches, and albums. Dr. Martin Luther King, Jr. incorporated the lyrics of this hymn into several of his sermons, and the hymn was played at Winston Churchill's funeral. Many Americans, however, take great offense to the song, feeling it to be a hateful and un-Christian rant against southern soldiers.

The hymn summons God to bring justice to those who have wrecked havoc over the land and over its people. In other words, the hateful ways of the people are so great that only God can bring about vengeance. In the context of this novel, "the grapes of wrath" may be interpreted as the greed, self-interest, and selfish ways of the landowners and of the banks – all of which lead to the suffering of thousands of migrant workers.

The "grapes of wrath" is also a Biblical reference to the Book of Revelation, passage 14:19-20:

So the angel swung his sickle to the earth and gathered the clusters from the vine of the earth, and threw them into the great wine press of the wrath of God.

Make no mistake, the squishing of "the grapes of wrath" is a violent and emotional image, and one that is closely associated with the widespread oppression of a people and with the darkest chapter in American history (slavery). The "grapes" image also makes us think of the spilling of blood.