Sorry it's been so long since I posted about making the acid beer. Finally getting around to doing a write up on it. Acid beer is simply a lactic beer that can have some brett in it if you desire. It's used to spruce up fruit beers, make beers tart, make beers sour, take a sour beer and add a bit more acidity and complexity. The lactic acid is created by lactobacillus rather than pedio because lactobacillus works so much quicker and doesn't ever get into a state of 'ropey-ness'.

To make a acid beer create some wort ~1.020-1.040 in strength. Pasteurize the wort (either by bringing the wort up to ~160F or boiling - Depending on flavor of wort you prefer). Don't add any hops. Different strains of lacto have different optimal fermentation temps.. so pitch the lacto and maintain whatever temp is best suited for your strain. (some good info can be found on the Milk the Funk wiki.) If you're not using a cultured strain of lactobacillus (ie lacto from grain husks etc...) drop the pH to < 4.5 prior to adding your wild yeasts. This lower pH will help prevent other things from thriving in your wort while the lacto will be unaffected. If adding brett add it after the lacto has had time to get the wort as sour as possible. Once the lacto/brett have done their thing it's best to put the acid beer into a vessel where it will not have much/any air contact. A keg is ideal for this.

When you need to add some tartness to a beer you have a couple options. You can blend the acid beer with your other beer and then keep the resulting beer cold and serve... or you can pull the acid beer and pasteurize (so it doesn't start fermenting again in your blend). After you pull some of the acid beer just take some second runnings from your next batch of beer and add it to the acid beer keg. Keeps the lacto and brett active and replenishes your acid beer in just a matter of days.

Below is the pH reading from my acid beer I made a couple weeks ago.