My recent writing foray into sour and wild homebrew territory started with a discussion of the yeast and bacteria used to make a sour ale and continued through an explanation of one of the easier sour ales to brew, the Berliner Weisse. The amount of specialized knowledge it takes to craft a perfect lambic, Flanders or wild ale at home is so vast that I probably won't spent too much more time on the topic, but I want to give the more adventurous homebrewers an idea of what they should expect when making an attempt.
Brewing a Berliner Weisse with Lactobacillus is probably not all that different from making any other homebrew, aside from the fact that it takes longer for the beer to finish. Once you delve into the world of the funky Brettanomyces or the tart Pediococcus, homebrewing takes on an entirely different dimension.
Homebrewing any sour or wild ale usually starts off exactly the same as brewing any traditional beer. You can make an extract style recipe, brew-in-a-bag, or an all-grain recipe. Fermentation starts out the same way, by cooling the wort, transferring to a sanitized carboy and pitching the primary yeast. Sometimes the sour bugs are added at the same time as the normal yeast, and sometimes you wait for a couple of weeks, and add them when you transfer the beer to a secondary fermentation vessel.
After adding Brett or Pedio into the beer, the first few weeks might seem completely normal. If the beer is still fermenting, there will be a foam krausen on the beer for a few days. The airlock will bubble for a couple weeks until the primary fermentation is complete. Once the fermentation settles down, you may notice a thin, grey film forming on the top of the beer. While seeing something like this on the surface of a normal homebrew would be a cause for alarm, it is perfectly normal when going through a wild fermentation. The film is called a pellicle and it's a basic defense mechanism of both Brett and Pedio, protecting the bugs in the beer from exposure to air and bacteria.
As the beer matures over the next few months, the pellicle can grow heavier and take on a thick, mold-like appearance. Don't be worried if the top of your beer looks like the sour cream you left in the back of your refrigerator for a year. It may be gross looking, but it is a perfectly normal part of the development of wild and sour ales. In fact, many experienced sour ale homebrewers embrace the idea that an unpleasant looking ale today will produce a delicious wild homebrew down the road. If you look around different homebrewing forums, you may find topics titled "Show us your pellicle", where brewers post photos of their offensive looking brews.
As a wild ale ages, the pellicle may become too heavy for the beer and sink to the bottom of the carboy just like the krausen. It also might stay floating on the top of the beer as it ages over a year or two. Either way, when you decide your beer is finished conditioning and you rack it to a keg or bottling bucket, try to leave as much of this behind as possible. While the funky covering won't hurt your beer, it's never a good idea to pick up floaties that may end up in your bottles.
Once your beer matures for a year or two it should be ready to bottle. If you bottle too soon, not only will the flavors be underdeveloped, but your beer may also grow an unsightly pellicle inside the bottle.
The first thing to think about when bottling is whether there is enough active yeast in the beer to produce carbonation. After a year of aging, the bacteria may still be active, but the yeast that you pitched have likely gone dormant. That's why it is always recommended to add an additional package of yeast at the same time as you add the sugar solution when you bottle. This yeast isn't going to do enough work to add flavor, so using the inexpensive and clean flavored Safale US-05 usually works best. I think it's a good idea to add the yeast to the beer itself, and not the sugar solution, so you don't have to worry about killing the yeast with a solution that's too hot.
Even if you add additional yeast and the right amount of sugar, you may find that your ales brewed with Brett or Pedio carbonate more slowly than the average beer. Pediococcus produces lactic acid, and Brettanomyces can lower the pH of the beer. These factors can inhibit the ability of yeast to produce carbon dioxide. Usually storing the bottles for an extra few weeks at a higher temperature (mid 70s) fixes the issue.This isn't a problem that affects all sour ales, but I do hear about it from time to time. Of course, if you serve your sour ale in a keg, then you can force carbonate the beer to avoid the issue of low carbonation.
Here is the recipe for my most recently completed sour ale, a sour saison. The base saison recipe is fairly standard, with the use of American hops instead of the typical European varieties. In addition to the French saison yeast I added Wyeast's Roeselare Ale blend, which is a mix of a wide variety of sour and funky yeast and bacteria. This ale aged for just over a year before it was ready to be consumed.