It’s probably the most frequently asked question asked about Oktoberfest: “Why is it called Oktoberfest if it’s in September?”

As Oktoberfest beers hit the shelves and Oktoberfest parties are held at breweries and pubs across the city, it’s an excellent jumping-off point for exploring both the festival and the brew that bears its name.

The short answer is that Oktoberfest is Oktoberfest and not Septemberfest because it was first held in October — Oct. 12, 1810, to be exact.

On that date, Crown Prince Ludwig (later King Ludwig I) married Princess Therese of Saxon-Hildburghausen. As king, Ludwig had trouble currying the favor of his people — after years of protests, including the Beer Riots of 1844, he would abdicate the throne in 1848 — but he at least got things started on the right foot by inviting the citizens of Munich to celebrate with him in front of the city gate.

Despite our current association with beer, it was horse racing that turned a one-time wedding celebration into an annual tradition. The main event at the royal celebration was a horse race that closed the festivities. It was such a big hit that the royal family decided to hold them again the next year, and thus Oktoberfest was born.

Over time, the festival grew bigger and evolved. The horse races were eventually dropped in 1960. Small beer stands that provided refreshments to the crowds evolved into large beer tents, each one sponsored by a different Munich brewery.

And, yes, as the celebration was extended, the beginning of Oktoberfest crept up into late September to take advantage of the warmer weather.

So where did Oktoberfest’s signature beer come from? This requires us to delve into a little bit of brewing history. You may have heard of the Reinheitsgebot — the famous German purity law that said beer could only be brewed from malt, hops, water and (once it was discovered) yeast.

Well, it’s not the only beer-related law the Bavarians enacted. Back in 1553, a law was passed that only allowed beer to be brewed between Sept. 29 and April 23. The basis for this was simple: Heat is the enemy of beer.

While fermenting, it can lead to the overproduction of esters and phenols, which give beer off-flavors. While conditioning, it can increase the risk of infection and speed up spoilage. So in the days before refrigeration, it was in everybody’s best interest to restrict brewing to the cool months.

Even the fastest beers take roughly two weeks to be ready, so while a brewer could start back up at the end of September, fresh beer wouldn’t be available until mid-October at the earliest. In order to make it through the summer, brewers would increase their output in March and April.

And while warm temperatures may have been the enemy of beer, alcohol and hops were known to help preserve it. As such, Bavarian brewmasters would produce a stronger, hoppier beer designed to last all the way to October, and they named it Märzen after the month in which it was brewed (“März” in German).

So the original Märzen, brewed long before Oktoberfest existed, was dark, hoppy and strong. This would change somewhat over time, however. New technology in kilning malted barley allowed for lighter beers, and in 1841 a Viennese brewer began using a lighter malt (called, appropriately, Vienna malt) that produced a copper-colored brew.

It was marketed as “the Vienna way” and became the predecessor to today’s Vienna lagers (modern examples include Metropolitan’s Dynamo and Great Lakes’ Eliot Ness).

Then, in 1871, Munich’s Spaten brewery “re-Bavarianized” the beer, using a slightly darker malt (called, appropriately, Munich malt). It’s a subtle difference but one that would give a more bready, less toasty flavor.

Also right around the same time, the refrigerator was invented, making it easier to store beer for months without spoilage. In response, Bavarian brewers cut back on the hoppiness of the beer (as it would no longer be needed as a preservative) consistent with the other malt-forward beers that are brewed in southeast Germany.

Eventually, they ended up with the malty, copper Oktoberfest beers (or, alternatively, “Festbier”) you find today.

Now, there is one final twist to the story. If you actually go to Munich for Oktoberfest, you’ll find the beer they’re pouring there isn’t copper at all. It’s the same golden yellow that you’d expect from a pilsner or other light German lager. Essentially, it’s a slightly stronger version of a Munich Helles (the traditional German lager of Bavaria).

So at what point did German Oktoberfest beers begin to lighten up and why did American ones stay darker? I’m afraid I don’t have an answer to that question, but it’s something to keep in mind should you find an imported Oktoberfest beer on tap.

Imports aside, Chicago-area breweries have begun embracing the style. You can find Oktoberfest beers from Metropolitan, Revolution, Two Brothers, Goose Island, Baderbräu, Church Street and Three Floyds at your local beer store.

And there’s a good chance your local brewpub has one on tap as well. Try a few and note the variations in sweetness, toastiness and hoppiness. And once you find one you like, stock up — they’ll go fast while watching football or sitting around a campfire.