The Session #40: Session Beer

Erik over at Top Fermented hosts this month's version of the Session and chose a topic that's homophonically appropriate. Session beers. Erik asks:

What is your definition of a session beer? Is it, as Dr. Lewis suggested at the Craft Brewers Conference this year, "a pint of British wallop" or is your idea of a session beer a crisp Eastern European lager, a light smoky porter, a dry witbier, or even a dry Flemish sour?

Is it merely enough for a beer to be low alcohol to be considered a session...