Please explicate the following lines from Keats' "Ode to a Nightingale." O for a draught of vintage! that hath been Cool'd a long age in the...

In these lines the speaker, Keats himself, is only
expressing the wish that he had something to drink and that he could get thoroughly
intoxicated. Keats was a young man, but he was developing a strong liking for
intoxicants. Many creative writers have a liking for alcohol and drugs which can be
dangerous, as I believe Emerson noted in his essay "The
Poet."

In the beginning of this poem Keats mentions hemlock
and an opiate, which would probably be a mixture of opium and alcohol. Later in the poem
he thinks of the musk rose as "the murmurous haunt of flies on summer eves"--in other
words, as a sort of pub where the flies hang out and get drunk on the nectar the flower
produces.

Keats was troubled by thoughts of death. Several
members of his family had died, and he himself expected to die of consumption. A number
of his poems deal with thoughts of death, including "Bright star, were I as steadfast as
thou art," and "When I have fears that I may cease to be." There was no cure for his
disease, so he tried to escape from thinking about it by at least two ways--drinking and
writing poetry. In "Ode to a Nightingale," which he wrote while listening to one of
these melodious birds late at night in a friend's garden, he is simply saying that he
would like to get drunk and escape from his morbid thoughts--but he just doesn't have
anything to drink. So he decides that he will try to escape in his imagination, which he
calls "the viewless [invisible] wings of poesy."

Keats
excelled in sensuous descriptions. He was not a deep thinker, but had a powerful visual
imagination. The lines quoted in your question are nothing but a description of the kind
of wine he wishes he had. He would like a whole beaker (about a quart). It would be a
red wine from the south of France. No such wine is produced in England; it would have to
come from the wine country of Europe.

The best lines in
this stanza are:

readability="8">

O for a beaker full of the warm
South!
 Full o the true, the blushful Hippocrene,
  With beaded
bubbles winking at the brim
     And purple-stained
mouth.

The warm south held a
strong attraction for Keats. He felt that the warmth of southern France or Italy might
heal him, or at least make him suffer less than he did in cold, damp England. He
actually went to Itay to try to recover his health. He died there and is buried beside
another great English poet, Percy Bysshe Shelley, with whom he is often compared. The
Merriam-Webster online dictionary gives the followiing definition
of Hippocrene:

readability="6">

:  a fountain on
Mount Helicon sacred to the Muses and believed to be a source of poetic inspiration

Evidently Keats like to
drink for poetic inspiration as well as for escape from his thoughts of death.

Everyone must have noticed how the little
bubbles collect at the top of a glass of wine and cling to the rim and could be said to
be strung together like beads. These little bubbles pop and might be said to be winking.
A person's tongue does become purple-stained when drinking red wine. This type of
imagery is characteristic of Keats' poetry and is the best thing about most of it. The
entire poem is full of vivid visual descriptions that will take the sensitive reader
along with the poet into the world of the immortal nightingale. F. Scott Fitzgerald
loved Keats and borrowed the beautiful phrase "tender is the night" from the fourth
stanza for the title of his best novel.