The song, Old Mountain Dew, seems to date back only to Bascom Lamar Lunsford. His quote here is from 1949 and appears in the booklet of Smithsonian Folkways CD 40082, 1996.

"This song is entitled 'Old Mountain Dew.' Possibly a footnote would be well here. About 1920 I composed the words and the tune to this song, and I put it on a Brunswick record about 1928. Of course, it was somewhat stilted, but it did very well as a record. But following that, the eminent singer 'Scotty,' Scott Wiseman of Lulu Belle and Scotty fame, added some more modernized stanzas, sang it, put it on a record, and it was re-popularized. Now we hear it on every hand by the folk singers and entertainers there with their own words, and the tune has stayed very much the same way, but it's well to know the growth of the thing. So I will give just as I composed it in 1920."

[You can hear this recording at the Internet Archive.]

OLD MOUNTAIN DEW
As recorded by Bascom Lamar Lunsford, 1928. (Brunswick 219-B)

On my first day in court, I wish to report
Then witness a story so true
When the State closed its case a young man raised his face
And began all the facts to review
Oh, they call it that old mountain dew
And those who refuse it are few
While I know I've done wrong the temptation is strong
When they call for that mountain dew.

Oh, the deacon drove by in his auto so shy
Said his family was down with the flu
And he thought that I ought to just get him a quart
Of good old mountain dew
Yes, he called it that old mountain dew
Said those who refuse it are few
So I thought that I ought to just get him a quart
Of good old mountain dew.

The doctor who phoned just to see me alone
One night about half-a-past two
Said he'd close up his mug if I'd fill up his jug
With good old mountain dew
Yes, he called it that old mountain dew
Said those who refuse it are few
So I closed up his mug when I filled up his jug
With good old mountain dew.

The conductor said with a nod of his head
"My wife she never knew
That I take my fun when I'm out on my run
So bring me a quart or two."
Of good old mountain dew
For those who refuse it are few
But his wife said to me, "You can bring me three
By the time his train is due."

My attorney began to turn the lid on the can
I knew then my case was lost
Said His Honor to me, "I will set you free
If you will pay the cost."
For they call it that old mountain dew
And those who refuse it are few
"But you acted the man when you took that stand
To swear what is so true."

Bascom does this with just his own claw hammer banjo accompaniment. I really recommend this album for those who like the old songs. It contains 18 songs recorded in 1928 and 1949. Included is a version of The Mermaid Song, Bonny George Campbell, Old Stepstone, and Death of Queen Jane, which has an interesting line, "The red rose of England shall flourish no more."