Schlüssel Stike clone

(5 gallons/19 L, all-grain)
OG = 1.061  FG = 1.015
IBU = 38  SRM = 12  ABV = 6%

Ingredients
12.4 lbs. (5.6 kg) Pilsner malt
2.5 oz. (71 g) Weyermann Carafa® Special II malt
8.6 AAU Hallertau Tradition hops (30 min.) (1.3 oz./38 g at 6.5% alpha acids)
10 AAU Perle hops (30 min.) (1.3 oz./38 g at 7.5% alpha acids)
1 tsp. Irish moss (15 min.)
White Labs WLP036 (Düsseldorf Alt), Wyeast 1007 (German Ale), or SafAle K-97 yeast
¾ cup corn sugar (if priming)

Step by Step
I currently use all Weyermann malts for my German beers. Feel free to substitute any high-quality malt of the same type and color from a different supplier. However, it is critical that the Carafa® Special only be substituted with another dehusked malt. Otherwise, the beer will turn out roasty. The Düsseldorf brewers often use whole hops, but pellets are seen more often these days. Just make sure that the hops you use are German-grown varieties.

The water profile in Düsseldorf favors chloride-to-sulfate at 1.26-to-1 and is moderately hard. If your water is soft, a bit of gypsum and calcium chloride will help.

A step mash is standard for altbier. The step mash for this recipe starts at 133 °F (56 °C) and then progresses through 144 °F (62 °C), 158 °F (70 °C), and 169 °F (76 °C). Keep the first rest short, just long enough to see that you hit your strike temperature. Then rest 20 to 30 minutes each on the next two rests and finally rise to the mash out temperature. Sparge slowly with 170 °F (77 °C) water, collecting wort until the pre-boil kettle volume is around 6.75 gallons (25.5 L).

The total wort boil time is 90 minutes. Add the Hallertau and Perle hops with 30 minutes remaining in the boil. Add Irish moss or other kettle finings with 15 minutes left in the boil. Chill the wort to 63 °F (17 °C) and transfer to an open fermentation bucket or bin. Aerate thoroughly if using a liquid strain and then pitch the yeast.

The beer should warm with fermentation activity. If it appears to be fermenting too hot, above 73 °F (23 °C), you can move the fermentation to a cooler area. If fermentation seems sluggish at all after the first 24 hours, move fermentation to a warmer area. With healthy yeast, fermentation should be complete within a few days, but do not rush it. 

If you wish to more closely mimic the real thing, you can rack the beer over to a keg with a spunding valve when it reaches 1.016 SG and let natural fermentation develop carbonation. Alternatively, ferment it out completely and then force carbonate or rack to a bottling bucket, add priming sugar, and bottle. Target a carbonation level of 2.8 volumes. After a month or more of cold conditioning at near-freezing temperatures the beer should be ready to enjoy.

Extract with grains option: Replace the Pilsner malt with 7 lbs. (3.2 kg) of Pilsen dried malt extract. Begin by placing the crushed Carafa® malt in a muslin bag and steep it in 4 gallons (15 L) of water as it heats up to 170 °F (77 °C). Remove grains, allowing the liquid to drip back into the kettle. Remove from heat and stir in the dried malt extract. Stir until completely dissolved. Bring wort up to a boil and stir in the hops. Boil for 30 minutes.

After the boil is complete, chill to 63 °F (17 °C) and top up fermenter to 5.25 gallons (20 L) with water. 

Follow the remainder of the all-grain recipe for fermentation and packaging instructions.