Berliner Weiss is a simple sour beer. You can use raw grain to get the lactic sourness, but it will also stink out your apartment and make you want to wrech. Here is the basic process without that problem:
Obtain some Lactic acid bacteria. Wyeast 5335 Lacto is good. I have used Lactobacillus Acidophillus probiotic pills from Walmart successfully. This is what will sour the wort, and to make a quick sour, the wort needs to be soured before adding the yeast.
Lactobacillus does not like hops. The Wyeast Lacto will tolerate a little (maybe 10 IBUs max, but don't push it. The probiotic pills will not tolerant any IBUs, so don't add any hops.
A Berlliner Weisse is traditionally a wheat beer, but normal malt will be fine.
Step 1: Make a starter with the lacto, no hops. Keep warm (90-100 F for 5 days). Taste a small amount. If sour go to step 2. If not sour, leave another day. When sour, go to step 2.
Step 2: Make wort to about 1.036 (1 lb LME to 1 gallon). No hops. You don't need them. And pitch starter. Keep as warm as you can (90 to 100 if you can). Taste a small amount. If sour go to step 2. If not sour, leave another day. When sour go to step 3. Remember, once you pitch the yeast, the souring will slow down considerably or even stop.
Step 3: Lower temp to normal fermentation temps and pitch yeast and aerate. If you really want some hops in the beer, now is the time to add them. Maybe make a quart to half gallon amount heavily hopped. However, this beer really doesn't need any hops.
Beer should be clear in 2 weeks ready to bottle. I usually go 3. You can add fruit at this time if you want too. Beer will be ready to drink once carbed.
A Berliner Weisse is a very refreshing low alcohol beer.