Home Made Wine

What is the correct social etiquette when presented with a glass of home made wine that would best be used to clean brushes after varnishing doors?

I still don't have it correct obviously as a spluttering cough followed by an involuntary shudder only served to draw the ire of Jola who told me in no uncertain terms that I had offended the hospitality of our hosts. Personally I am not sure I offended them at all as they only smilingly said "It is very good, yes?", which is really too much of a rhetorical statement to warrant any other response than a meek nod.

Problematically I have been invited back to help "finish the batch" as they are expecting a baby and the wife can no longer drink alcohol. I think I feel a migraine coming on and will regretfully have to decline.