Possessive brand names

Grammar is generally a strong point of mine, but I have a question here that I think might be tough to answer definitively. My problem arose when wanting to write down a question someone asked involving a brand of beer. The beer is always named John Smith's bitter ale, in the sense of being the ale of John Smith, presumably the beer and never rendered as simply 'John Smith'. If my friend was to offer me a drink, mentioning that he had some of these in his kitchen how would this be written down? obviously if the beer were called John Smith it would simply be:

'Do you want a drink? I've got some John Smiths in the kitchen'

Given, however, that the brand name is John Smith's, would it be:

'Do you want a drink? I've got some John Smiths' in the kitchen'

Which would be my guess, or something entirely different?

Thanks in advance,

An ale loving grammar nut.