What makes a Kolsch a Kolsch?

I went today to get the stuff to make a batch of Kolsch and the store was out of Kolsch yeast. I got German Ale Yeast (Wyeast 1007) instead. Now, most recipes I've seen for Kolsch beers do say that 1007 can be used, so I'm not worried about that. But it got me to wondering, if the yeast is not the determining factor, was is it exactly that makes a Kolsch a Kolsch?

Other than being brewed in only one city in Germany to be called Kolsch officially(can't remember which one, HB99 where are you when I need you). A Kolsch is made with ale yeast but it is fermented at lager temps, at least thats what I've been told and is how I did my Kolsch. Lagered for 4 weeks before bottling. Came out fine.

2nd Street Brewery said:

Other than being brewed in only one city in Germany to be called Kolsch officially(can't remember which one, HB99 where are you when I need you

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The city is Cologne or Koeln as it is called in Germany.

A Koelsch is a cleanly fermented light colored ale (some fruitiness is allowed) . It is still fermented at ale temperatures (though on the lower end) and cold lagered for about 4 weeks. The bitterness is usually between 20 and 30 with little or no hop aroma/flavor. The original gravity is between 1.040 and 1.050 (about 12 deg Plato in Germany). Though wheat malt is allowed for top fermenting beers in Germany, many Koelsch breweries are still using only barley malt, hops, water and yeast.

These properties (light, lightly hopped and top fermenting) make this a prime choice for home brewers that want to have a lager like beer but don't have the resources to brew true lagers.

Kai