Lots of good info about making sour fruit beers in this article with a recipe which uses Yakult as the lactobacillus source.
(5 gallons/19 L, all-grain)
OG = 1.047 FG = 1.008
IBU = 9 SRM = 3 ABV = 5.2%
6 lbs. (2.7 kg) Pilsner malt
3 lbs. 8 oz. (1.6 kg) wheat malt
3 AAU Magnum hops (30 min.) (0.25 oz./7 g at 12% alpha acids)
5.5 lbs. (2.5 kg) fresh guava, peeled, frozen, then thawed
(3) 80 g bottles “Yakult 40” brand probiotic drink (Lactobacillus casei Shirota)
SafAle US-05 or other clean, highly attenuative ale yeast
7⁄8 cup corn sugar (if priming)
Step by Step
Adjust brewing water with lactic acid, calcium sulfate, and calcium chloride to achieve a mash pH of 5.3 with 70ppm of calcium and a sulfate:chloride ratio of 1:1. I would use reverse osmosis (RO) water and adjust all brewing water to a pH of 5.5, then add ½ tsp of calcium sulfate and calcium chloride to the mash.
This recipe uses a step mash with rests at 122 °F (50 °C) for 5 minutes, 153 °F (67 °C) for 70 minutes, and 169 °F (76 °C) for 10 minutes. Sparge and collect 6.5 gallons (24.5 L) of wort.
Boil the wort for 10 minutes to sanitize without hops, then chill to 113 °F (45 °C). Acidify with lactic acid to a pH of 4.5. Pitch the Lactobacillus (probiotic drinks) directly into the boil kettle. Seal the boil kettle using plastic wrap. Purge with CO2 periodically. Keep the temperature at 113 °F (45 °C) using an electric heater or other method for 36 hours or until the pH reaches 3.5. Perform a second boil for 70 minutes, adding the hops with 30 minutes remaining. Chill the wort to 64 °F (18 °C), pitch the yeast, and ferment until SG 1.014. Add the guava and allow fermentation to finish.
Clarify if necessary. Rack the beer, prime and bottle condition, or keg and force carbonate.