"mixed ale"?

[Kim & Rima McKinzey]

I forwarded the question to a friend who I thought might know
something.  (For one thing, he's done a great deal of research into
old English drinking songs)  Here was his reply.

>I have not the clue of a Dutchman.  Possibly it refers to ale fortified with
>strong spirits, like gin.   Or, another possibility, an ale made up of the
>lees left by the beer engines as they exhausted the cellared kegs, poured
>off into a common butt as the kegs were switched.
>
>Just educated guesses however.   Feel free to pass them along at their face
>(nil) value....