I do my Berliners in about 3 weeks grain to glass. Here's my method:
Grain Bill (5.0 gallon batch)
4 lbs crushed Wheat Malt (or 3 lbs Wheat LME)
4 lbs crushed Pilsner Malt (or 3 lbs Pils LME)
0.5 lbs UNCRUSHED extra Pilsner/Two-Row Malt for sour inoculation
Hop to taste (traditional BWs have no hops, those that do are very low IBU<10)
Liquid German Ale Yeast (traditional) or S-05 dry yeast
Procedures
1) Mash crushed malts at 146-148F for at least 20 minutes, holding back 0.5 lbs of uncrushed malt. You may find it useful to complete this step with a smaller pot at a 1.0-1.25 qt/lb grist ratio to make it easier to handle (especially BIAB brewers that would typically use full water volume).
2) After 20 minute mash, cool to 110F, add the 0.5 lbs of uncrushed malt to the mash and stir it in.
3) Cover the mash with cling wrap, etc. If possible, purge the O2 from between the grain bed and the cling wrap. Easy way to do this is take the gas disconnect off your CO2 tank, put the tube under the cling wrap, allowing space for O2 to escape, and open your CO2 tank for a couple seconds.
4) You’ll need a method to maintain the temp at about 90-120F for 2-4 days. The higher the temp in this range, the faster it will sour. A couple suggestions:
a. A 40 watt light bulb will maintain a 100-110F temp in an insulated cooler/closed fermentation chamber, or even in the oven with just the internal oven light on. Wrap the pot in a towel to help insulation.
b. Space heater in an interior closet/bathroom. Make sure you do this in a way that will be safe for 2-4 days, and not a fire hazard!
c. Keep the bottom/sides in contact with a heating pad, wrapping the pot in towels/blanket. Make sure you do this in a way that will be safe for 2-4 days, and not a fire hazard!
5) At 100F, you should get a light sour in 2 days, moderate sour in 3 days, and prominent sour in 4 days. Taste the mash in about 8 hour intervals throughout to test sour levels to your personal tastes, being careful to maintain the CO2 blanket (repeat O2 purge, if necessary). Remember that you will add water to get to your full volume, diluting the sour level, so plan accordingly.
6) Once you have your desired sour level, complete your brew day as normal. The boil will stop the souring process by killing the lactobacillus, and lock in the sour profile of the existing lactic acid.
7) Cool/Pitch/Ferment as normal.
TIPS and TRICKS
 Lactic acid is relatively dense and will screw up OG readings, so don’t worry if something seems a little off. Also, some species of lactobacillus produce alcohol, and some don’t, so there may be up to 10-15% attenuation/gravity loss during your sour mash.
 Your sour mash SHOULD smell pretty pungent. In particular, a healthy lactobacillus sour mash should smell like cooked corn.
 You WILL need to either make a proper yeast starter or pitch multiple packs for this sour beer. The saccharomyces strains in the German Ale yeast/S-05 HATE the low PH of the lactic acid, and will stall/be sluggish without a proper pitch rate. Yeast nutrient always helps as well. Also oxygenate well prior to pitching!
 A Berliner Weiss should be carbonated to 3.0-3.5 volumes CO2.
 Great with real fruit additions in secondary or with flavored syrups!
