For more about brewing pilsner with extracts as well as fermenting lager under pressure using a spunding valve, see No Rests for the Wicked: Extracting the Elegance of No-Pressure Pilsner.
Batch size: 4.75 gallons (18 liters)
9 lb (4.1 kg) pilsner liquid malt extract (LME)
1 lb (454 g) Carapils
HOPS & ADDITIONS SCHEDULE
2 oz (57 g) Saaz at 60 minutes [19 IBUs]
2 oz (57 g) Saaz at 30 minutes [14 IBUs]
½ tsp (2.5 ml) Irish moss or ½ Whirlfloc tablet at 15 minutes
2 oz (57 g) Saaz at 10 minutes [7 IBUs]
1 oz (28 g) Saaz at flameout
Fermentis SafLager W-34/70, White Labs WLP833 German Bock Lager, or other lager strain of choice
Mix your usual brewing water 50/50 with distilled water to make 5 gallons (19 liters) and heat it to 154°F (68°C). Mill the Carapils and steep at 154°F (68°C) for 30 minutes. Turn off the heat, add the LME, and stir thoroughly. Boil for 70 minutes, adding hops and Irish moss or Whirlfloc according to the schedule. Chill to about 65°F (18°C) and transfer to a clean, sanitized corny keg. Fill to about 4.75 gallons (18 liters), aerate well, and pitch the yeast. Seal the keg, connect a spunding valve, and set it to 6 PSI. On Day 5 of fermentation, set the valve to 12 PSI. Transfer the finished beer to bottles or a clean keg and lager (i.e., chill) for at least 2 weeks before consuming.
Filling the keg not quite full (i.e., about 4.75 gallons/18 liters) allows some head space for the fermentation and spunding to work under pressure.