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It is important to mention that sour brewing in general has very few well-established "rules". Many methods can be used in conjunction with other [[Brewing Methods]], and new methodologies are constantly being developed. Many of the methods used are determined by the types of microbes the brewer is working with. An article of this length cannot encompass all mixed fermentation methods. Instead it will provide a "big picture" view of the general methodologies. Towards this end, we divide mixed fermentation methods into two approaches: the traditional long fermentation method and an increasingly popular, short fermentation method. They are divided here as a device to illustrate the philosophy of each and facilitate the discussion of the techniques used for each methodology. The distinction of these two methods is however somewhat artificial, indeed many brewers use elements of both approaches to achieve their desired results. More detailed information can be found in Michael Tonsmeire's pivotal book on sour brewing, "American Sour Beers".

=''Sour'' Mixed Fermentation-The Basics=

Beer styles that can be brewed using this method include [[Berliner Weissbier]] and the subcategories of [[American Wild Ale]], which include [[Mixed-Fermentation Sour Beer]] and [[Soured Fruit Beer]] <ref>[http://www.bjcp.org/docs/2014%20BJCP%20Style%20Guidelines%20%28DRAFT%29.pdf BJCP 2014 Style Guidelines Draft.]</ref>. European sour styles such as [[Lambic]], [[Gueuze]], and [[Fruit Lambic]], technically can only be produced by [[Spontaneous Fermentation]]. [[Flanders Red Ale]] and [[Oud Bruin]] styles can be brewed using pure cultures, but can also be brewed using spontaneous fermentation or a mix of using pure cultures and spontaneous fermentation.

The most basic method for making a mixed fermentation sour beer is to brew some simple wort (fresh extract or all grain) that is low in IBU's. Iso-alpha acids can inhibit many species and strains of LAB. Keeping the wort less than 6 IBU's is recommended in general, unless the brewer has information about their LAB culture that indicates that they can tolerate more. Mash hopping is one technique that can be used to limit the IBU's by about 70% <ref>[http://www.homebrewersassociation.org/attachments/presentations/pdf/2014/Putting%20Some%20Numbers%20on%20First%20Wort%20and%20Mash%20Hop%20additions.pdf Putting Some Numbers on First Wort and Mash Hop additions. David Curtis. NHC 2014.]</ref>. If hops are not required (commercial brewers may be required to use hops, while homebrewers aren't), they can be completely excluded from the recipe.

This method has been used by some brewers before a lot was known about sour brewing microbes and before some of the more current techniques were popularized (such as [[Sour Worting]], or the other methods mentioned in this article). This method is best described by the following: Brewer X has a beer, and perhaps that beer didn't come out the way they wanted, or perhaps there is some other motivation, but Brewer X decides that they want this beer to be sour. Great idea, right? Perhaps. [[Lactobacillus]] tends to prefer simple sugars, which are required for lactic acid production. [[Pediococcus]] can break down some of the larger chain sugars that are left over in the beer from the [[Saccharomyces]] fermentation, but there may not be enough of those sugars to create even a moderate level of acidity. If the beer contains more than 6 IBU's, the bacteria may be largely inhibited. The [[Brettanomyces]] in general should create a nice range of flavors (see [[Funky Mixed Fermentations]]) in secondary, so this could benefit the beer. However, due to the lack of sugars, finished beers which a brewer may attempt to sour often do not get very sour at all. Some brewers have reported good results with this technique (particularly professional brewers who use barrels; see "American Sour Beers" by Michael Tonsmeire for more information), but in general if the brewer is going for a truly sour beer, it is better to use another method.

The grain bill and production for the wort doesn't have to be complex. For sour blonde ales a simple grain bill of about 70% Pilsner malt and 30% malted wheat can be used (these can be replaced by Pilsner and wheat unhopped extracts for the extract brewer. See [http://byo.com/videos/item/975-lambic-brewing Lambic Brewing by Steve Piatz] for a good extract recipe). Some crystal and a small amount of roasted malts an be used for sour brown ales. Some higher chain sugars or even starches can be included for beers that will be aged for a long time and include Brettanomyces, or Brettanomyces and Pediococcus (Pediococcus generally should not be used without Brettanomyces. See the [[Pediococcus]] page for more details). Performing a [[Turbid Mash]] is the traditional way to include starches in the wort, however other methods such as steeping some oats or flaked wheat during the boil can also impart starches that won't be converted to sugars by the mash <ref>[http://www.homebrewtalk.com/f127/adjuncts-starches-sour-beer-448529/ Homebrewtalk Discussion started by Amos Brown aka 'Metic']</ref>. This step is completely optional, however it may be very beneficial to make sure some higher chain sugars or starches are available in the wort if the brewer wants to rely on Pediococcus for producing most of the acidity. Extract brewers can use 0.25 lbs. (0.11 kg) of Maltodextrin <ref>[http://byo.com/videos/item/975-lambic-brewing Lambic Brewing. Piatz, Steve. Brew Your Own Magazine. October, 2004.]</ref>, or hot steep a pound of flaked wheat, flaked oats, or carapils malt.

Once the wort is produced and chilled, the mixed culture can be pitched as normal. If using a mixed culture from a commercial yeast lab, it is usually recommended to not make a yeast starter with it because the starter will throw off the intended ratios of the microbes. Instead of buying a single mixed culture, a brewer can create their own mixed culture by combining their own ratios from single cultures of yeast and bacteria. A single mixed culture can be supplemented by adding pure cultures from different yeast labs as well. Another suggestion that often helps produce a higher quality sour beer is to supplement the mixed culture with a [[Commercial Sour Beer Inoculation]]. In general, the more diversity of microbes, the more complex a sour beer can potentially be. Using a [[Sour Worting]] method in conjunction with this method can help increase acidity that may not otherwise be produced by some commercial blends (Wyeast Roeselare is known for this characteristic, for example).

==Wort Production==

The grain bill for a short fermentation sour can be based on nearly any style. The wort, however, is generally designed to be highly fermentable, in contrast to the low fermentability of wort used in the long ferment method. This is because the order and timing of microbial inoculation is used to control acidity and fermentation characters rather than depending on the selective availability of carbohydrates to particular microbes in the long ferment method. A few modifications to grain bills can be made to increase the fermentability of the wort and accomplish the full attenuation of the wort in a relatively short period of time. These modifications include lowering or removing crystal malts from the recipe and mashing for 90-120 minutes at 149F. Extract brewers can steep 2-3 lbs. of crushed, malted 6-row at 149F in their kettle with their extract in order to increase the fermentability of their wort.

[[File:Fast Sour Graph.jpg|thumb|upright=2.5|Conceptual graph of Fast Souring microbe and media dynamics|Conceptual graph of fast souring microbe and media dynamics. Y-axis for each microbe group depicts relative activity which combines in a conceptual sense: growth, acidification of wort, attenuation and production of flavor compounds. Plot drawn by Drew Wham based on concepts discussed in American Sour Beer <ref> Tonsmeire, M. (2014). American Sour Beers. Brewers Publications </ref> and Wild Brews <ref> Sparrow, J. (2005). Wild Brews: Beer Beyond the Influence of Brewer's Yeast. Brewers Publications</ref> . ]]

Matt Miller outlines a ''three stage fermentation'' process on his blog article [http://sourbeerblog.com/understanding-brewing-blending-lambic-style-kriek/ Understanding, Brewing, and Blending a Lambic Style Kriek] <ref>[http://sourbeerblog.com/understanding-brewing-blending-lambic-style-kriek/ Understanding, Brewing, and Blending a Lambic Style Kriek. Miller, Matt. Retrieved 1/24/2015.]</ref>. See the article for a much more detailed process. Matt was also interviewed about his process by James Spencer on the [http://traffic.libsyn.com/basicbrewing/bbr01-22-153stepkriek.mp3 BasicBrewing Radio podcast]. In summary, his process is as follows:

# For the last two months of aging, fruit, spices, and/or oak can be added directly into the fermenter. Also consider [[Blending]] with other sour beers.

== Reusing a Sour Yeast Cake==

Reusing a sour yeast cake can often provide great results. Brewers have reported success repitching on very old yeast cakes (2 years) without getting off flavors from yeast autolysis. After several months, [[Saccharomyces]] tends to die off due to the low pH in a sour beer. The bacterias and [[Brettanomyces]] tend to survive the lower pH, and their cell counts can be high in even an old yeast cake. By pitching new wort on an old sour yeast cake, these microbes (particularly the [[Lactobacillus]]) have access to the simple sugars in the wort <ref>[http://www.themadfermentationist.com/2009/11/brewing-sour-beer-at-home.html Tonsmeire, Michael. The Mad Fermentationist. Brewing Sour Beer at Home. Last paragraph in the "Inoculation" section. Retrieved 2/19/2015.]</ref>. In general, washing the yeast cake is not necessary.

As with all methods, the species and strains of the microbes being used should always be taken into consideration. Experimentation and repeated processes should be carefully employed by the brewer in order to find the best results for their cultures. For example, using different strains of Saccharomyces cerevisiae as the primary fermenter can produce widely different results.

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[[Category:Techniques]]