Without becoming overly technical, we nevertheless should have a working knowledge of how beer is made in order to understand what the "session beer" style really is.
Broadly speaking, you add water to some sort of grain (malted barley, wheat, rye, etc.) and let it sit. Then yeast is introduced -- it feasts on the sugars in the grain and "gives off" both alcohol and carbon dioxide as byproducts. The result if it were bottled would taste like alcoholic oatmeal -- way too sweet. So some sort of bittering agent is added (hops are the most common, but dandelion or other botanicals also could used).
The short moral is that craft brewers (and craft beer drinkers) are obsessed with flavor. They don't want "fizzy yellow stuff." They want aroma. They want mouthfeel. They want finish. And all of that is very easily accomplished if you add A LOT of stuff.
I'm certainly not implying that making a triple IPA or an 18% Imperial Stout is easy. But it's easy to understand that the reason there's a lot of flavor (and alcohol) concentrated in each sip is because there's a dense concentration of ingredients. It's like putting five teabags in your cup. It takes a lot of careful finesse to coax out a balanced and flavorful product if you're trying to limit one of the essential components: Remember that the alcohol in beer is the inevitable byproduct of yeast fermenting the grain.
The session beer is the mellifluous confluence of aroma, mouth feel and finish in a glass that doesn't break 4.5% alcohol. But since the term "session beer" speaks to a grouping unified only by a kind of "Not X," it becomes somewhat difficult to pin down thematic or stylistic continuity amongst the beers.
Drake's Alpha Session is a highly aromatic pale ale with notes of tropical fruits. The Bruery's Hottenroth Berlinerweisse is tart. Eagle Rock's Solidarity is an English Black Mild with nutty nose and a chocolate finish. The most profound characteristics shared among them are an attention to balance and a relatively low alcohol content. Keeping the alcohol under 4.5% means that you're able to sit back and actually order a second beer.
Jason Bernstein is co-owner of the Golden State.