Sapwood Cellars’ Nu Zulund clone

(5 gallons/19 L, all-grain)
OG = 1.055  FG = 1.007
IBU = 0  SRM = 3.5  ABV = 6.3%

Sapwood Cellars’ one and only kettle sour was a sour IPA showing off Wai-iti and Waimea hops from New Zealand. The result was fruitier than some of our fruited sours, with big lime and stone fruit aromatics. The post-souring whirlpool serves both to kill the Lactobacillus and impart “kettle character” from the hops.

Ingredients
6.75 lbs. (3 kg) Rahr Standard 2-row malt
3 lbs. (1.4 kg) Rahr Pilsner malt
0.875 lb. (0.4 kg) Crisp oat malt
0.875 lb. (0.4 kg) BestMalz spelt malt
6 oz. (170 g) Waimea hops (hop stand) 
6 oz. (170 g) Wai-iti hops (dry hop)
3 oz. (85 g) Waimea hops (dry hop)
~10–15 mL 88% lactic acid 
Omega Lactobacillus blend
Omega Yeast OYL-200 (Tropical IPA) or White Labs WLP644 (Saccharomyces “Bruxellensis” trois) yeast
Yeast nutrient per manufacturer’s directions

Step by step
Mash at 157 °F (69 °C), adding calcium chloride to achieve 150 ppm chloride. If needed to achieve a mash pH of 5.2, add phosphoric acid. Collect wort and boil for 60 minutes. At the end of the boil, add lactic acid to achieve a pH of 4.4. Chill wort to 95 °F (35 °C). Pitch an active starter of Lactobacillus. Don’t worry about maintaining this temperature. Allow to sour to a pH of 3.3 (or as desired), approximately 12–24 hours. Heat to 175 °F (79 °C) and add whirlpool hops and nutrient. Allow to sit for 40 minutes before force chilling to 66 °F (19 °C). Transfer to a fermenter,  aerate, and pitch yeast. Ferment at 68 °F (20 °C). 

Once the gravity stabilizes, chill to 55 °F (13 °C). Transfer to a purged keg with dry hops placed in screens. Dry hop for three days at 55 °F (13 °C),
agitating once or twice daily for 30 seconds. Transfer off the hops to a serving keg. Pressurize to reach 2.5 volume of CO₂.

Partial mash option: Replace 2-row and Pilsner malts with 3.5 lbs. (1.6 kg) extra light dried malt extract and 1.6 lbs. (0.73 kg) Pilsen dried malt extract. In a muslin bag, heat the crushed oats and spelt in 3 qts. (3 L) of water to 164 °F (73 °C). Mash at around 157 °F (69 °C) for 45–60 minutes. Remove the grains and wash with 1 gallon (4 L) of hot water. Bring volume up to 6 gallons (23 L) and stir in the malt extract. Follow the remainder of the all-grain recipe.