If you’re starting to get more serious about beer, you may have noticed a style frequently referred to as “Märzen/Oktoberfest.” Why the slash? Even if you only know just enough German to follow Hogan’s Heroes, you probably know that märzen is German for March. What does that have to do with October? Is the beer brewed in March? October? Both? Neither?
Brewing in Summer ist Verboten
In 15th century Bavaria, brewing in the warm months usually did not turn out well. Brewers didn’t know it at the time, but beer was much more susceptible to bacteria in the warm summers than when it is cooler.
To put an end to all these massive drainpours, a decree forbade brewing during the warm months from the end of April to the end of September. Because of this, brewers busted their humps in March, using the remainder of the malt and hops leftover from the previous Fall to make beer that was a bit stronger than normal, which they then lagered link to our ales v. lagers piece. That is, they stored it someplace cool, like a cave.
Märzen/Oktoberfestbier Becomes Official
In October, it was time to drink all of that March beer and make room in the barrels for the next batches, hence the association with Oktoberfest. Märzen became official in 1841, when Spaten Brewery labeled it as such for that year’s Oktoberfest. A few decades later, Spaten introduced a märzen style beer at Oktoberfest and called oktoberfestbier, named after the braumeister, Herr Oktoberfest. (That last bit is not true. If this is for homework, leave that part out.)
So What About Vienna Lager?
Valid question. At the same time that Spaten Brewery introduced the first officially labeled märzenbier, Dreher Brewery near Vienna introduced a märzen style and called it a Vienna lager.  It is not a coincidence that Anton Dreher was friends with Gabriel Sedlmayr, the brewer at Spaten who created that brewery’s first official märzenbier. In fact, they worked together to develop the two styles.
So Get to the Point—What’s the Difference?
Although there is considerable fuzziness among the distinctions among the three beers, we can consider a few general guidelines. In Germany, only the six Munich breweries may call their märzenbiers Oktoberfestbier. All others use the märzen appellation. That’s only in Germany, though, and the distinction between märzenbier and oktoberfestbier ends there.
Vienna lager generally differs from märzen/oktoberfestbier in a few ways. The malt used for märzen/oktoberfest beers, called Munich malt, is darker than the Vienna malt used for Vienna lagers. Also, whereas märzen/oktoberfest beers tend to have a more pronounced maltiness, Vienna lagers are often a bit hoppier and drier.
So in a nutshell: unless you are at Oktoberfest, you needn’t concern yourself with the difference between märzenbier and oktoberfestbier. And the only difference that might be helpful to know between märzen/oktoberfest beers and Vienna lager is that if you prefer a more pronounced maltiness, stick with the former. If you prefer hoppier, drier beer, stick with the latter.