So i have a bottle of Jos. Bring company 'Barrel of Beer' root beer. I know it has to be at least 30 years old, but i'm not really sure. how might i find out the original date?

Interesting. Are there other details on the bottle? Can you post / link to or email photos?
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Bottoms up!
Kevin Guske

“So here’s a tribute toast with root beer in hand to you and the many mugs of suds along your happy trails.” --Charles Wysocki, artist and root beer fan, 1928-2002

Just to clarify, are you sure it's Barrel of Beer, or is it Barrel of Root Beer? I found a photo of a Barrel of Root Beer bottle - shaped like a barrel from 1982 in the book More Root Beer Advertising & Collectibles. Unfortunately, the book doesn't mention any other information about the bottle or brand.

If that's the same as your bottle, I'd love to get a photo of it for the site.
_________________
Bottoms up!
Kevin Guske

“So here’s a tribute toast with root beer in hand to you and the many mugs of suds along your happy trails.” --Charles Wysocki, artist and root beer fan, 1928-2002

i was posting this message for a friend of mine who is the owner of the bottle. I'll have to stop by and get a look and take some pictures of it.
I'm pretty sure though, it does look like a barrel, but says 'barrel of beer' on it, not 'root beer'