For malt extract:
Kölsch is a pale, well-attenuated ale from Köln (Cologne), Germany. The style can be viewed as a hybrid or intermediate style located inbetween various pale European lagers and ales.
2021 BJCP 5B - Kölsch characteristic ingredients: "Traditional German hops. German Pils, Pale, or Vienna malt. Attenuative, clean German ale yeast. Occasional small use of wheat malt. Current commercial practice is to ferment around 15 °C, cold condition near freezing for up to a month, and serve fresh."
Vital Statistics: OG: 1.044 – 1.050, FG: 1.007 – 1.011, IBUs: 18 – 30, SRM: 3.5 – 5, ABV: 4.4 – 5.2%
The base malt is continental pilsner malt or European pale malt. Some European malt companies sell a specific Kölsch base malt.
Use restraint with specialty malts. Zainasheff suggests choosing one specialty malt and keeping the amount to 5% or less of the malt bill. Vienna is a common choice, but note that one of the source experts dislikes Vienna and Munich in this style.
Older American recipes often suggested 15 to 20% wheat malt, but this amount is now understood to be too high. The current BJCP description describes "small use" of wheat malt.
Extract brewers can try 100% light or extra light malt extract. A possibility is a small amount of wheat malt extract.
The hops should be traditional German or continental European varieties, like Hallertau, Saaz, Tettnang, and Hersbrucker. American hops bred from Hallertau like Mount Hood might be acceptable choices for Americanized versions. Some of the reviewed recipes have a small late hop addition at 10 minutes, but this is not essential. Large hop flavor and aroma are not appropriate. Aim for a BU/GU ratio of .5.
The recommended yeast are Kölsch ale strains. Both wet and dry versions are available. The primary fermentation temperature is a bit cooler than most ales, such as 58 to 64F (14 to 18C). A lagering period at cooler temperatures is a common practice.
Beer-analytics.com Kölsch analysis
Dornbusch, H. (2013, July-August). Helles and Kölsch: Germany's summer session beers. Brew Your Own, 26 - 34.
Kowald, E. and Dornbusch, H. (2018, May-June). Take me to your liter: Tips and recipes foor brewing Germany's regional classic beer styles. Brew Your Own, 58 - 71.
Szamatulski, T., & Szamatulski, M. (2001). Kölsch and Porter: Ale from Köln, porter from London. Brew Your Own, 19 - 22.
Wiliams, F. (1998, January-February). The queen of Köln: A visit to the court of Germany's kölschbier. Brewing Techniques, 36 - 43.
Zainasheff, J. (2009, May-June). Kölsch: The beer of Cologne. Brew Your Own, 19 - 22.