Sour and Mixed Culture Beers
"Sour" is a broad description for beers that have an intentionally acidic or tart flavor profile, made by employing or encouraging lactic acid producing bacteria. Like a sourdough culture used in breadmaking, the lactic acid bacteria (LAB) work in conjunction with yeast to acidify and ferment the beer. ("Clean" beers that unintentionally become sour through cross contamination are not typically cause for celebration).
"Mixed culture" is a relatively recent term applied to brewing techniques that use a combination of traditional and alternative yeasts and bacteria. Mixed cultures usually include more than one of the following microorganism groups: Saccharomyces, Brettanomyces, Lactobacillus, or Pediococcus. Depending on which cultures are utilized, these beers may or may not be sour/tart/acidic, and they may or may not have other unique attributes generally associated with Brettanomyces (farmyard "funk", phenols, tropical esters, etc). A mixed culture beer can be funky without being sour and vice versa.
"Wild and Spontaneous Fermentation" makes use of yeast and bacteria that are present in the natural environment, for instance on the skin of fruit, on raw grain, within wood brewing vessels, on the walls of breweries, carried by insects, or even in human facial hair or furniture. These kinds of cultures -- captured via bioprospecting -- generally fall into the category of mixed culture, containing both saccharomyces (but rarely brettanomyces) and lactic acid producing bacteria.
While there is a lot of historical (non-European) precedent for gluten free mixed culture / sour beers, these are generally not styles of beer that can be found commercially. Even within the conventional (barley-based) beer market, sour and mixed culture beers are still a niche commodity. Using alternative yeasts and bacteria does present some logistical considerations for breweries focused on making "clean" (Saccharomyces-only) beer (GF or otherwise), and perhaps mostly for that reason, it is rare to find commercial gluten free operations dabbling in this field. Gluten free homebrewers have much more opportunity to experiment and fill this void.
European and Non-European Mixed Culture Beers
Before the science of microbiology was well understood and applied to brewing, sour and mixed culture brewing was likely a fact of life throughout the world, with "spoilage" organisms living in fermentation and storage vessels. Cooler temperatures along with ingredients such as hops and other herbs served to inhibit LAB growth. Given sufficient time and the right environmental factors, however, most beers likely would have become more acidic over time, and/or developed flavor elements assonciated with Brettanomyces.
European Brewing Tradition
In Europe, several styles have developed over centuries that embrace acidity and "funk". This is especially true in Belgium, but with examples in Germany and elsewhere. Before the isolation of specific domesticated yeast strains -- and the introduction of more sterile brewing practices -- many beers, especially those aged in wood rather than those consumed while relatively fresh -- would have been more likely to develop characteristics of microorganisms beyond saccharomyces. Some traditional European styles known for their sour and/or Brettanomyces character include:
- Flanders Red
- A mixed-culture beer from the Flemish region of what is today Belgium. Fermented with Saccharomyces, then soured primarily by Lactobacillus strains. Aged in wood barrels containing Lactobacillus, Pediococcus, Brettanomyces, and Acetobacter.
- Flanders Brown (aka Oud Bruin)
- A maltier version of Flanders Red (historically not a separate category). Like Flanders Red, acidity comes primarily from Lactobacillus. Today it is aged in steel, not wood, so less likely to develop Brettanomyces characteristics.
- Berliner Weiss
- A low alcohol northern German wheat beer, soured with lactobacillus, and historically exhibiting fruity (versus phenolic/barnyard) brettanomyces character.
- Suggestions for gluten free brewing:
- Use pale millet or rice malt (or a combination) to mimic some of the bready/doughy contributions that would normally come from wheat.
- Include a high protein (and low lipid) source such as raw millet, quinoa or lentils to emphasize head formation and retention usually attributed to wheat
- Wort should be highly fermentable (do not want dextrins that could otherwise emphasize more barnyard flavor components of Brettanomyces)
- No boil or very short boil to retain doughy character of grains and limit protein degradation
- Sour either as a mixed fermentation (allowing lactic acid bacteria to continue working over longer timeframe) or using kettle-sour method to acidify and then briefly boil to stop LAB. Acidity should be moderate (tart not sour)
- Use a highly attenuative, neutral, non-phenolic Saccharomyces strain (e.g. German Ale or Kolsch)
- Avoid stressing yeast: sufficient pitch rate, nutrients, cool fermentation temp to start
- Use a fruit-forward Brettanomyces strain that will focus on ester production rather than phenolics and funk
- A spontaneously fermented beer made from a combination of malted barley and wheat. Lambic is a protected term. Outside of Belgium they may be referred to as lambic inspired.
- Gluten free brewers can use spontaneous fermentation and mixed culture methods to create lambic inspired beers, choosing different grains of course. For instance a combination of raw and malted millet, rice, and buckwheat.
- A blend of old and new barrel-aged lambic beer. Geuze is a protected term. Outside of Belgium, they may be referred to as geuze inspired, or more commonly as blended, barrel aged, spontaneously fermented beer.
- A warm-fermented sour beer originating from Goslar (now Germany), flavored with salt and coriander.
- A sour and smoky beer from Thuringia area of Germany. Grain bill historically included equal parts pilsner malt, wheat malt and smoked malt. Unlike gose, would not have contained salt or spices.
- A gluten free version of this could include biscuit rice malt, some Munich or Vienna millet malt, some raw millet and/or buckwheat, and some home-smoked pale rice or millet, or a commercial variety available from GFHB. Ferment with a German ale yeast (SafAle K-97) and a Lactobacillus pitch.
- Old Ale
- A strong English style beer typically aged in wood vessels that would frequently contain Brettanomyces ("British fungus").
Conventional (barley-based) craft brewers, especially in North America, have adapted sour and mixed culture techniques. While some of the above styles imply specific practices -- and even geographical claim to the use of the terms -- there is an active community of amateur and commercial brewers working within -- and often times -- outside these style guidelines.
Non-European Brewing Tradition
With diverse brewing ingredients and environmental conditions, brewing outside of the European tradition has been anything but homogeneous. Without hops and other LAB-inhibiting ingredients, and especially in warmer climates, many traditional beers would have likely been (and continue to be) mixed culture with a tart to eventually sour dimension. Where traditional beer remains popular alongside commercial European-tradition products, some acidity is usually expected and desired. (References)
Important considerations for gluten free homebrewers
Gluten free brewers may already be accustomed to dedicated equipment to avoid the risk of cross contact with gluten sources. When using alternative yeast and bacteria sources (e.g. Brettanomyces and Lactobacillus), it is typically a good idea to maintain separate "cold side" (post boil) equipment to avoid unintentionally spreading these non-Saccharomyces microorganisms. Tubing, airlocks, plastic fermenters, and other items that would come into contact with these beers should be the priority.
Acquiring alternative yeast and bacteria in gluten free medium
Gluten free brewers who want to avoid the risk of gluten cross contamination have fewer options than those without that restriction. While a variety of saccharomyces cerevisiae strains and lactic acid bacteria are available in gluten free media, that is generally not true for brettanomyces and popular mixed culture blends. Bottle dregs from mixed culture barley beers are not an option without further culturing. Options generally include:
- Sourcing from a commercial yeast supplier on gluten free media
- Creating (and then maintaining) a mixed culture from multiple gluten free sources
- Culturing yeast or bacteria on agar
- Wild yeast capture
Souring Process Alternatives
Quick or kettle souring
Generally involves souring the wort (or less commonly, souring the grain) through the introduction of a lactic acid bacteria (LAB) and then arresting the acidification when it reaches the desired level through boiling. LAB sources can include probiotic products (e.g. live culture kombuchas, or Good Belly) but has been made easier with the introduction of gluten free LAB pitches like Lallemand WildBrew Sour Pitch and Lallemand Helveticus.
A high level summary of the process:
- Produce wort from gluten free grains or extracts (sorghum / rice syrups). Wort with higher glucose levels (simple sugars) will produce more lactic acid than those with more complex sugars.
- Add the lactic acid producing bacteria
- Keep the wort at the optimum temperatures for the bacteria for 12-48 hours. (30 - 40C +, 86 - 104F +). This can be easily done in an all-in-one system with a lid on.
- Check pH and flavour on a regular basis to determine acidification level.
- When the wort has reached the desired acidity, boil the wort to stop further acidification.
- Cool and pitch yeast.
Lactic Acid Producing Yeast
This is an unusual and relatively new category of yeast that has been selected or genetically modified to produce both alcohol and lactic acid. Unlike the technique of acidifying wort before fermentation, this approach aims to significantly lower the pH level during fermentation. The benefit is that it is fairly simple to do —- there are really no additional steps outside of a regular brew session. (Note that making a wort that is higher in glucose, versus longer chain sugars, will produce higher levels of lactic acid). A downside relative to the quick souring method (acidifying pre fermentation) is that there is less control over the level of acidity.
Souring in the fermenter (traditional mixed culture approach)
Using a variety of yeast and bacteria sources is a more historical / traditional approach to making sour beers that continue to develop during a long ferementation and aging period (often over multiple years). This approach is highly associated with Belgian producers of lambic and other "sour" beer styles. Mixed culture fermentation has also been adopted by "new world" breweries looking to make more complex beers than can be achieved with the relatively quick souring methods above. Mixed cultures can include various strains of saccharomyces cerevisiae, brettanomyces, pediococcus, and lactobacillus. These cultures generally develop over long periods of times to become "house strains", and brewers of these beers will often blend different barrels of beer with different qualities to achieve a desired outcome.
Spontaneous Fermentation and Wild Yeast
Commercial Gluten Free Examples
Occasionally, commercial gluten free brewers have released mixed culture beers in local markets or in taprooms only. Example references:
- Glutenberg - "Assemblage". BAOS video podcast. 22:17 discussion of barrel aged, mixed culture beers.
- Dos Luces - Chicha fermented with Pichia kluyveri (a separate genus of yeast within Saccharomycetaceae family).
- Yeast and bacteria for gluten free brewing (including Brettanomyces and lactic acid bacteria)
- Milk the Funk Facebook group
- Milk the Funk Wiki
- American Sour Beers (Brewers Publications)
- Wasp Yeast Beer is Making a Buzz, Food and Wine magazine
- Rogue Brewing Beard Beer, Wikipedia
- Beer brewed from Roald Dahl's writing chair
- Milk the Funk Podcast on Bioprospecting
- "Flemish brown, red or red brown? How Michael Jackson invented a beer style out of thin air", Lost Beers blog, Roel Mulder, retrieved July 14, 2020
- Milk the Funk Wiki: Berliner Weissbier
- Milk the Funk Wiki: Lichtenhainer