In order to give you some context for better understanding this very short poem's central metaphor, it is important to note that it was published within a longer volume of linked jazz-inspired poems called Montage of a Dream Deferred. Hughes considered the work a single book-length poem of jazz-inspired impressions of the Harlem neighborhood of Manhattan where he was living and writing in the years after World War II.
A montage is a juxtaposition of fragmentary components ordered to create a coherent meaning, and many of the other poems emulate the rhythm and textures of African-American music. Hughes suggests through the title that the collection of sketches and riffs on contemporary Black life in Harlem has as its ultimate subject the notion of the "dream deferred," and this poem serves as an introduction of that recurring theme.
As a national mecca of the fruits of African American culture in the first half of the twentieth century, like music, literature, politics and art, Harlem was an epicenter for the collective aspirations of Black America. Yet the fabled neighborhood also contained the same poverty, oppression, and disenfranchisement that Hughes would have known from his native Missouri and its Jim Crow traditions in line with the former Confederacy.
Far from being a promised land, slick, soulful, and gritty Harlem is also a place that robs, cheat, kills and exploits, breaking hearts and crushing dreams. There, one encounters the pinnacle of American success and establishment for those who pursued their dreams undauntedly. But the dream of many is deferred—passed over or put off—because the consequences of a marginalized existence render them defeated, devoid of confidence and courage, or worse. The various images of rupture and decay in the poem suggest that the costs of not pursuing a free and authentic existence despite the structural obstacles is spiritual death.
This short poem by Langston Hughes actually comprises a series of metaphors about the central question of a "dream deferred" and what happens when this occurs. However, all of the metaphors run along similar lines: Hughes imagines the deferred dream as a variety of perishable items, incorporating foodstuffs such as meat which will rot if left too long, and an old sweet which will "crust over" if it is not consumed in time, as well as the comparison to a raisin drying up in the sun.
Hughes also suggests that a deferred dream might take on the character of a sore which will eventually burst and "run over" after a long period of festering.
Finally, he compares the deferred dream to a "heavy load" which will weigh upon the dreamer until, potentially, it explodes.
These are all varied metaphors, but they convey the same thing. Hughes is suggesting that a dream cannot simply be deferred indefinitely and expected to remain the same. Rather than remaining as fresh as it ever was, the dream will begin to fester and go bad. It may even change the character of the dreamer who has been forced to wait. Ultimately, the dream may express itself in unexpected ways, if it does not dry up completely, and could even cause harm if left until it explodes.
In the poem "Harlem," Langston Hughes creates a central metaphor surrounding a dream by comparing a dream to multiple images of death and destruction in order to ask what happens to a "dream deferred," meaning a dream that has been delayed in being fulfilled.
He first compares a delayed dream to a "raisin in the sun," implying the dream is dried up and shriveled. Next, he asks if a delayed dream becomes infected "like a sore." Untreated cuts become infected and painful, leading to other major health problems, sometimes even death; therefore, in comparing a delayed dream to an infected wound, Hughes likens a delayed dream to something that causes severe pain and is destructive, even deadly. A third comparison is of a delayed dream to "rotten meat," which is meat that has gone uneaten for so long it is now dangerous for anyone to consume. By comparing a delayed dream to inedible meat, Hughes is wondering if dreams that go unfulfilled for a long time become so painful that they are noxious to the dreamer.
A fourth comparison is that of a delayed dream to sugar or syrup, which implies the dreamer starts seeing the dream as having been sugarcoated, meaning more appealing than it actually is. An example of seeing a dream as sugarcoated could be an African American wishing for an end to segregation but being led to believe that sharing the world with white people would lead to even more abuses and inequalities. By being led to believe such a fallacy, an African American may believe his or her present situation is better than the situation he or she dreams of, which would make him or her see the dream as sugarcoated.
Two final comparisons are that of a delayed dream to a load that is too heavy to bear and to something that explodes. Hughes's final comparison of a delayed dream to an explosion is the most powerful because it significantly contrasts with his other images of death and destruction. By comparing a delayed dream to an explosion, he implies that when dreams are prevented from being fulfilled, the dreamer builds up enough energy until the dreamer explodes in a burst of energy to fulfill the dream, just as we saw with the dawning of the Civil Rights Movement.