The can is also an indication that you're back in a bona fide nation, as Frank Zappa put it, "you can't be a real country unless you have a beer and an airline - it helps if you have some kind of a football team or some nuclear weapons, but at the very least you need a beer."

Canned beer does have an image problem.

Canned brews tend to be distinguished by everything that is wrong with lowest common denominator brewing: a deluge of overcarbonated, thin and watery lagers differentiated only by the specious claims of their respective marketers and the gaudy colors on their tins. There are certainly exceptions, but in modern beers, the badness has nothing to do with the packaging.

Originally beer cans were made from tin (or steel) which despite being lined with a lacquer, leached iron into the beer creating a metallic flavour. In a modern aluminium can, if the layer of lacquer is damaged by severely denting the can, the off flavour that develops is sulphury rather than metallic due to galvanic reactions. Minute amounts of aluminum do get into the beer but it doesn't create that ferrous tang.

When beer is canned in aluminium, the metallic taint in beer is most often caused at the brewery by poor quality brewing equipment leaching iron into the brew. While this may be a problem for your average Third World brewery (or home brewer), newer stainless steel setups are unlikely to be bleeding rust into your suds.

So why is there a widespread observation of metallic-flavoured beer from cans if the aluminium causes a sulphurous taint?

Many beer snobs have explained away the "beer from aluminium cans tastes metallic" as a trick of your own perception rather than an objective observation. If you expect that a beer will taste like sucking on a rusty nail, then chances are that you'll perceive a metallic note in the beer whether it exists or not. Being as kind-hearted as I am, I'd rather not write off people who drink straight from cans as having their tastes outwitted by their own brains.

Once poured into a glass, it is impossible to accurately guess the container from whence the beers came. You'll be able to distinguish between different batches of the same beer, but not whether they came from a can or a bottle.

My theory is that the act of drinking from a can causes the metallic taste.

When you drink out of a can you abrade your lower lip on the can's edge, shearing off a few skin cells and (possibly) drawing a little blood. Try sucking on the inside of your lower lip. It tastes metallic. The taste that is imparted from drinking straight from an aluminium can is not the can but is the taste of you.