1. Line the 7.5 gallon kettle with mesh grain bag, fill with 2.1 gallons tap water and bring to 159°F. Remove from heat.
2. Mash-in by slowly adding Pilsner and wheat malt into the bag. Stir for 2 minutes to prevent grain from clumping together. The temperature should equalize to about 149°F
3. Remove 3 quarts of the mash for the decoction, including a good mixture of both the grain and liquid. Add the Hallertauer hops to mixture and boil in a separate pot for 15 minutes. Stir frequently, and as foam rises to the top, skim and discard.
4. Add the entire decoction back into the mash. In a separate container, heat 3.7 gallons of water to 185°F.
5. After about 60 total minutes of mashing, mash-out by carefully pouring the 185°F water into the mash, stirring to equalize temperature to about 170°F.
6. Slowly raise grain bag out of the liquid, allowing wort to drain from the grain. Hold grain bag above the kettle for 5 to 10 minutes as the wort drains.
7. DO NOT BOIL. Cool the wort to under 80°F and transfer to a sanitized fermentation vessel.
8. Use a sanitized auto-siphon racking cane to remove enough wort to take a gravity reading with your hydrometer. Make a note of this number, since you will be using it to calculate the actual alcohol content when it's done fermenting. The reading should be around 1.035. Cover fermentor with a sanitized stopper and airlock.
9. Add 1 package of Safale US-05 and 2 packages of Lactobacillus. Ferment for 3 to 5 days at a temperature around 75°F.
10. Condition by allowing the beer to rest for at least a month. Taste samples weekly to determine sour flavor development.
11. Bottle when desired level of sourness and flavor have developed, up to 6 months, using enough priming sugar for a high level of carbonation.