I've been studying different types of wild beers a lot recently but am yet to have committed to brewing one or what style I want to start with. I am by no means an expert having tasted only a few and brewed none, but this seems like a good place to compile some of the research I have done.
I wish there were a better term than "wild" (as a true wild beer would, in my mind, refer to one made with local, self caught yeast) but many beers are often called wild because they use living components other than traditional brewers yeast (Saccharomyces) and are typically made with Brettanomyces (so called "wild" yeast) and potentially bacteria (notably Lactobacillus and Pediococcus) or because they share traits with beers which do have these microorganisms. There are many variations on what a "sour" or "funky" or "wild" beer is and for the sake of this article I will simply call them all "wild" as not all the beers I am referring to taste sour and many (even some made with Brettanomyces) do not taste "funky", while some beers that do not contain these traditional organisms (or acids) can taste sour or funky. While there are some classic styles known for their sour or funky qualities there are many wild beers being made today (and traditionally) which do not fall into easily defined categories. Instead of talking about styles I just wish to write about some methods of creating these types of beers that are commonly employed:
1. Adding (lactic) acid: Adding acid, usually lactic though I suppose others (malic or acetic for example) could be used, seems to be the least "craft" method of making a sour and might feel more like an industrial process or even "cheating" to some people. This is utilized by brewers sometimes alone or in combination with other methods to create a sour beer. As it sounds this process simply uses food grade acid, which can be added to the mash to lower pH or can be added at other stages for sour beers.
2. Sour Mash: A sour mash is achieved by adding raw grain to wort which has not had yeast added to it. The grain is covered in Lactobacillus (among other things) causing a quick souring of the beer. This can also be achieved, among other ways, by adding cultured Lacto. or with a yogurt culture. Brewer's utilizing this method typically hold the Lactobacillus innoculated wort at a warm but not hot temperature then add to the mash of the final beer to heat the wort after a few days of souring to kill any yeast and bugs and stabilize the sourness level. Anywhere from 10% to 100% of the wort can be soured in this manner, giving varied results.
3. Sour Malt: Sour malt, also known as sauermalz and acidulated malt, is a malt which is covered with lactic acid, hence lowering the pH of a beer it is mashed in. This can be used in non-sour type beers to slightly adjust the pH, as the sole provider of sourness if used in large amounts, or in combination with other methods to form sour beer. In most respects this process isn't much different from adding straight lactic acid in the end.
4. Pitching Brettanomyces without Saccharomyces: This process can be done with Brettanomyces as the sole yeast in which case a subtle fruity yeast character with flavors closer to a beer brewed without "wild" ingredients is produced.
5. Pitching bacteria (Lactobacillus) without Saccharomyces: This process is utilized sometimes by select craft breweries and homebrewers. This is most commonly used in small beers, most notably some Berliner Weisses. This method needs specialized (heterofermentative) bacteria which produce both lactic acid and alcohol and can survive conditions enough to fully attenuate the beer themselves.
6. Pitching in addition to Saccharomyces: This is the most traditional and probably the most common method of sour productions and is typically used to make all 6 of the BJCP approved sour styles. Whether added in primary or secondary (or traditionally as ambient yeast which are in the air/wood/fruit added to the beer) the idea here is typically to have the Sacc utilize simple sugars while Bugs and/or Brett work on more complex sugars and other side components to generate strong flavors ranging from tropical fruit, horse, goat and farmyard funk characteristics found derived from Brett to the tart and tangy flavors from Lacto to the biting, vinegary qualities from Acetobacter.
Hopefully I will soon have ventured into the world of funky and sour beers as I recently bought two yeast packages which come with additions to sacc:
White Labs American Farmhouse: A proprietary blend of belgian yeast and brett. I hope to make a brett saison somewhat similar to Goose Island's Sophie.
Roeselare Blend: This is essentially a lambic blend with various lacto and brett strains in addition to sacc. I plan to brew a sour brown ale with this pack, allowing it to age for upwards of a year.