Spontaneous Fermentation

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Spontaneous Fermentation, for the purposes of this article, refers to the inoculation of wort for fermentation with local ambient microbes. This is commonly achieved by use of open cooling such as in a coolship where the wort is left exposed to the air and allowed to cool naturally over night. Wild yeast and bacteria are introduced into the wort as it cools. Spontaneous fermentation is part of the traditional brewing method of Lambic [1].

Defining Spontaneous Fermentation

In the most romanticized view of spontaneous fermentation, the microbes which inoculate the wort in the coolship are sourced exclusively from the ambient environment outside the brewery. Scientific publications have suggested that in the case of some producers, these microbes may be resident in the brewhouse [2]. This is supported by the reluctance of lambic brewers to alter their facilities (remodeling, moving, painting, etc.) and the spraying of lambic on the walls of new buildings [3] [4]. The microbes responsible for spontaneous fermentation may also be derived from the oak barrels and/or foedres which are often used to hold the fermenting beer, especially if the barrels/foudres have not been thoroughly cleaned [5]. Many Belgian lambic producers thoroughly clean their barrels using hot water/steam, mechanical agitation (such as is seen at Cantillon), and/or burning sulfur [6]; however even the most rigorous cleaning likely does not fully sterilize the barrels. In the case of lambic brewers the microbes resident in barrels are spontaneous in origin, having been derived from years to decades of use in the brewery without any exposure to pitched cultures and the barrels may serve as a concentrating mechanism for the desired cultures. The role of barrels as an inoculating vessel is unclear as some producers report achieving excellent results in barrels new to the brewery and which are microbially clean [7] (~35 min in).

A spontaneous fermentation may also be achieved by inoculating small amounts of wort and growing up the spontaneously inoculated microbes to check for suitability. This is common in homebrew production [8] and allows for screening of the microbes to remove wild cultures with aggressive off flavors and/or mold. This is not unlike the potential of used oak barrels, where well performing barrels may be kept to inoculate subsequent batches while poorly performing barrels may be discarded and removed from the brewery. As different microbes survive and thrive in different environments, barrels or pre-screened and grown starters will probably not provide a complete profile of the microbes present in traditional spontaneous fermentation beers. However a combination of a coolship to inoculate the wort with ambient/brewhouse resident microbes combined with a form of pre-screening such as barrel re-use and/or spontaneous starters may provide the full microbiota present in traditional spontaneously fermented products. For the purposes of this page, beers receiving additions of isolated cultures or bottle dregs are not treated as spontaneous and are discussed under mixed-culture fermentation.

Brewing Methods

(in progress)

The traditional production of spontaneously fermented beer employs a few main processes and goals including the production of a dextrinous wort, high hopping rates (usually with aged hops), and inoculation of the wort with a coolship. Not all breweries producing spontaneously fermented beer employ these three techniques, but they are generally common among producers.

A dextrinous wort may be produced by different mashing procedures. The most traditional method of achieving this is through a turbid mash. With this mashing technique, unconverted starchy wort (which turbid in appearance) is pulled from the mash and heated to denature enzymes. These pulled runnings are then replaced by infusions of hot water as the mash is carried through a series of steps for conversion of the remaining grains. The starchy wort from the early 'turbid' pulls is carried to the boil with incomplete conversion, providing dextrins to sustain Brettanomyces and lactic acid bacteria in a prolonged mixed fermentation. Other methods to carry unconverted dextrins into the boil may be employed such as the addition of flour [9] passing hot mash runnings through flaked grains [10], or pulling mash runnings before full conversion without the prolonged processing of a turbid mash [10]. Whichever technique is employed, the goals are the same - to provide starches which Saccharomyces cerevisiae and Saccharomyces pastorianus cannot ferment and which can feed the diverse combination of other yeasts and bacteria present.

Traditional spontaneous brewers use high hopping rates of aged hops in a long boil. The high hopping rates help to regulate bacterial activity and select for the desired bacteria (Pediococcus rather than Lactobacillus. Aging of the hops lowers the flavor/aroma impact the hops provide and also lowers the bitterness. The aged ops still do provide some bitterness as both oxidized alpha acids and oxidized beta acids can contribute to perceived bitterness and measured IBUs [11]. Cantillon uses hops that are on average 2-3 years old at hopping rate of 250-300g/100 L (3.34-4.0 oz/gal) [7](~49 minutes in). Other producers use higher hopping rates . The use of significantly lower hopping rates may result in less bacterial inhibition and lead to different types of bacteria present. Some lambic producers are experimenting with the use of fresh dried hops in addition to or instead of aged hops [12] [13] [14]

A coolship is an open vessel used to cool wort by exposure to ambient air which traditional spontaneous fermentation brewers use to both cool their wort and to inoculate the wort with ambient microbes during the open overnight cooling. Traditionally, a coolship is a broad, open-top, flat vessel in which wort cools overnight. The high surface to volume ratio allows for more efficient cooling, which is important at commercial production scales. In addition this broad, shallow design maximizes the area of wort available for inoculation with ambient microbes. On a homebrew scale, where typical batch sizes cool more quickly, a wide shallow pan is not necessary to achieve appropriate cooling overnight given sufficiently low nighttime outdoor temperatures and the use of a wide shallow pan might result in cooling at a much more rapid rate than seen in traditional commercial production. Boil kettles and similarly shaped vessels are sufficient for overnight cooling for most homebrew batch sizes and may provide a rate of cooling more similar to that provided by coolships in commercial production sized batches [15]. However the aspect ratios of these sorts of vessels may limit the inoculation of the wort by ambient microbes due to the lower surface area for a given volume compared to traditional coolships. Cantillon targets a cooled wort temp of 18-20 C (64.4-68 F) after the overnight cooling [7] (~50 min in). Traditional producers only carry out spontaneous fermentation between fall and spring when nighttime temperatures are sufficiently low (max nighttime minimum of about 8°C [16]) to appropriately cool the wort overnight. The ambient microbial balance may also be more favorable during this time of year (--some sources say more bacteria in summer--), but inadequate cooling could result in similar results of enhanced acid production (similar to the effect of warm incubation in sour worting, see also Alternative applications of Spontaneous Fermentation below). Whatever the root of the different resulting beers based on time of season/ambient nighttime temperature, producers do report different times of year/temperatures exerting a strong influence on the final beer [7](~39 minutes in, ~54 minutes in).

Traditional producers of spontaneously fermented beer conduct fermentation for a long time period (1-3+ years) in wooden vessels. The long fermentation process allows the different microbes present to carry out their slow metabolism of the complex carbophydrates present in the beer, developing the flavors and acidity associated with spontaneous beers (-------). The wooden fermentation vessels are frequently oak wine barrels in the 220-400 L (58-105 gal) range but other woods such as chestnut are used and the vessels may also be large tuns or foeders holding upwards of 45 HL (about 1200 gal, or about 34 bbl). These barrels provide two primary benefits for the fermentation - they allow a small amount of oxygen permeability and they provide a environment which houses some of the microbes active in the fermentation (notably Brettanomyces, which can penetrate up to ---- (ref) into the wood and in some cases can metabolize compounds present in the wood such as cellobiose, which is produced from toasting of the wood) (----ref---). While a controlled micro-oxidation can be beneficial to the beer, too much oxygen exposure can lead to excessive acetic acid production (either from Brettanomyces or Acetobacter) (----ref).

On a homebrew scale a fair amount of attention has been paid to the topic of O2 permeability in different fermentation vessels and closures [17] [18] [19]. It has been suggested that sealing a glass carboy with a wooden dowel or chair leg can result in similar O2 permeability as a wine barrel. While this was quite a clever idea for replicating O2 exposure, this is not recommended as it can lead to breakage of the glass carboys [20]. While micro-oxygenation may be an important part of some spontaneous production it may be getting too much attention in homebrew carboy conditions [20] (see comments) relative to other controls such as temperature, microbes, and time. See the Barrel page for discussions on the barrels available to homebrewers.

Regarding fermentation temperature, commercial producers looking for balanced acidity and flavor/aroma complexity prefer cooler fermentation temperatures in the range of the high 50s to low 60s F (~13-18 C) [7] (~1:14 in), -----Armand ref. This temperature range allows slow and balanced fermentation by the diverse array of microbes present. Warming the fermentation too much results in enhanced production of acidity which is out of line with what the lambic producer is aiming for. This can be used to the advantage of the brewer when producing certain non-lambic inspired spontaneously fermented beers (see below, Alternative applications of spontaneous fermentation).

Some more industrial producers of Belgian lambic as well as smaller North American brewers employing spontaneous fermentation acidify their wort before primary fermentation. This may eliminate the enteric bacteria step [5] (see below, Microbial Succession During Fermentation). In addition it may act as a safeguard against botulism in the beer, which can grow at the typical pH range of unfermented and unacidified wort and whose spores can survive the boiling process [21]. The degree of botulism risk is not known, though if any reported cases of botulism poisoning from beer exist they are not known to us. Traditional lambic producers have been fermenting unacidified and spontaneously inoculated wort for decades to centuries, which suggests that the risk, if it does exist at all, is very small when following traditional lambic production methods. Furthermore, hops have antimicrobial properties against gram positive bacteria [22] and Clostridium botulinum, the bacterium responsible for botulism, is gram positive [23]. The degree to which Clostridium botulinum might be resistant to the antimicrobial properties of hops is unknown. Some suggest eliminating any potential worry of botulism by acidifying your wort before inoculation [21]. Whether or not this protects from botulism, it will influence the final beer by preventing enteric bacteria growth. In addition, acidifying may influence the activity of Pediococcus in a spontaneously fermented beer, including the development of "sick" beer, and may therefore alter the final beer [7] (~1:10 in).

  • Homebrew 15 Gallon Coolship

  • Homebrew 15 Gallon Coolship

  • 30 Barrel Coolship from Funk Factory

Microbial Succession During Fermentation

(In Progress)

Scientific research in Belgium and the US has shown a regular general pattern to the microbial succession of spontaneous fermentation beer. [24] [2] [25] [5]. This as been illustrated well by Raj Apte [26]. The first stage, which lasts for approximately 1 month [24] [27], is dominated by enterobacteria. Though enterobacteria contribute little in terms of gravity drop over the first month of fermentation, they may contribute aroma and flavor compounds and precursors during the initial stages of spontaneous fermentation [27]. Acidifying the wort to pH = 4 before cooling and exposing to ambient microbes in a coolship can eliminate the enterobacteria phase of spontaneous fermentation [5].

The second stage of spontaneous fermentation is dominated by Saccharomyces sp. (predominantly S. cerevisiae and S. bayanus). Most of the attenuation is accomplished during this stage, which lasts approximately 3-4 months [24].

The Saccharomyces dominated stage of fermentation is followed by prolonged and gradual acid and flavor development accompanied by the final points of attenuation. In some descriptions this is split into an "acidification phase" which is dominated by lactic acid bacteria (LAB), primarily Pediococcus, and a "maturation phase" driven by Brettanomyces [24]. Other sources describe these as one extended maturation phase with acidification from Pediococcus and Brettanomyces growth occurring simultaneously [5] [2] [25]. Note that many scientific publications use the terminology Dekkera rather than Brettanomyces. ----continue this

During the extended maturation phase, a beer may become "sick" or "ropey", though not all producers get this [7] (~1:10 min in) (also Vinnie on the sunday session and maybe lambic summit). This is the result of exopolysaccarides, which some Pediococcus strains are known to produce. These exopolysaccharides can be broken down by other microbes present in the beer relieving the beer of its "sickness" (this exopolysaccaride breakdown is generally attributed to Brettanomyces). A beer may also become "sick" in the bottle during bottle conditioning. This is likely due to enhanced Pediococcus activity from additional fermentable sugar, in the form of simple sugars or beer which has not completely attenuated yet. --sources for this--. A beer which is sick in the bottle will generally clear through the same process as a younger aging beer wen given appropriate time.

Alternative applications of Spontaneous Fermentation

Much of the above discussion has focused on spontaneous fermentation as applied to lambic and lambic-inspired brewing. Some brewers are applying spontaneous fermentation to yield beers quite different from lambic-oriented brewers. A notable example of this is De Garde, whose entire lineup of beers are cooled in a coolship and don't see pitched yeast [28] (excepting perhaps a bit of pitched yeast in some beers for bottling conditioning). De Garde produces a range of spontaneous beers including beers similar to berliner weisse by warm incubation after spontaneous inocculation [29]. By manipulation of parameters such as grist, hopping levels and incubation/fermentation temperatures, a diverse range of beers of spontaneous fermentation can be produced outside of lambic-inspired beers.

Spontaneous Fermentation versus Mixed Fermentation

Spontaneous fermentation yields the greatest diversity of microbes in the wort, including many outside of Saccharomyces, Brettanomyces, Pediococcus and Lactobacillus [2] [5] [25]. The degree to which these diverse microbes present during spontaneous fermentation are active and influence the characteristics of the final product is unknown, but brewers report in some cases upwards of 100 distinct microbes present and 24 different microbes which active and important in producing the character of their beers [7](~36 minutes in). Spontaneous fermentation may be conducted anywhere, though the microbes present in different environments and/or at different times of the year or from different cooling rates due to different ambient night time temperatures may be better or more poorly suited for producing a good tasting final product [28] [7](~39 minutes in, ~54 minutes in). In addition, many of the microbes active in commercial spontaneous fermentation derive from the brewery environment [2], which is a benefit that the average homebrewer likely does not have. This great range in the potential of spontaneous fermentation can produce some of the most complex beers in the world, but it can also produce undrinkable products.

Some brewers may opt for the more controlled techniques of Mixed Fermentation to approach the sorts of characteristics found in spontaneously fermented beers. Mixed fermentation employs the controlled pitching of different lab sourced microbes or bottle dregs. These may be pitched all at once or staggered to control the final product. This greater degree of control can limit some of the risk of poor outcomes and can allow a brewer to better achieve the beer they want; however this approach cannot yield the same microbial diversity of spontaneously fermented beer. For this reason, homebrewers may need to decide what degree of risk they are willing to take and what sort of final product they are after to determine which technique is right for them. Many use a hybridized approach of the two, combining open cooling for spontaneous inoculation with pitching of labs cultures and bottle dregs. While this is technically not spontaneous fermentation and it may yield different results from truly spontaneously fermented beers, it can be a good balance of the benefits of spontaneous fermentation (collection of ambient microbes to express regional terroir and a greater diversity of microbes present) with benefits of mixed fermentation (some pre-screening and greater control in dominant microbes to help select for a final beer of the brewer's preference). Ultimately the brewer must decide which approach, or combination of the two approaches, is right for them with regard to the desired flavor and aroma profile, adherence to tradition, timeframe, and risk of bad beer.

See Also

References

  1. ↑ The Mystery of Lambic Beer. Jacques De Keersmaecker. Aug 1996. Retrieved 05/05/2015.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Bokulich et al, 2012
  3. ↑ Cantillon Facebook post 5-February-2015
  4. ↑ Modern Brewery Age Weekly 23-October-2009 Article by Peter Reid with Frank Boon, accessed 7-May-2015
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Spitaels et al., 2015
  6. ↑ Conversation between Dave Janssen and Steven Sonck of De Cam, winter 2014
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 The Sour Hour Episode 11 with Rob Tod and Jason Perkins from Allagash, Jean Van Roy from Cantillon, and Vinnie Cilurzo from Russian River Cite error: Invalid <ref> tag; name "Spontaneous_Sour_Hour" defined multiple times with different content Cite error: Invalid <ref> tag; name "Spontaneous_Sour_Hour" defined multiple times with different content
  8. ↑ The Mad Fermentationist Spontaneous Starters, accessed 7-May-2015
  9. ↑ Burgundian Babble Belt discussion
  10. ↑ 10.0 10.1 Flat Tail on the Brewing Network, ~1:04 in
  11. ↑ Understanding How to Control Flavor and Aroma Consistency in Dry Hopped Beer. Dan Vollmer, Dan Sharp, Dr. Tom Shellhammer (Oregon State University). Oral presentation at the 2015 Craft Brewers Conference
  12. ↑ Cantillon Iris
  13. ↑ Cantillon Facebook Page post 22-Sept-2015
  14. ↑ Conversation between Dave Janssen and Jean van Roy of Cantillon, 17-Sept-2015
  15. ↑ Facebook post by James Howat
  16. ↑ Conversation between Dave Janssen and Armand Debelder of 3 Fonteinen, July 2011
  17. ↑ Raj Apte's O2 permeability table
  18. ↑ Better Bottle closure study
  19. ↑ Dan's video discussing airlocks and fermenters
  20. ↑ 20.0 20.1 Mad Fermentationist $8 homebrew barrel Cite error: Invalid <ref> tag; name "Mad_Fermentationist_Oak" defined multiple times with different content
  21. ↑ 21.0 21.1 James Howat presentation at NHC 2015
  22. ↑ Sakamoto and Konings, 2003. Beer spoilage bacteria and hop resistance.
  23. ↑ Clostridium botulinum Wikipedia page
  24. ↑ 24.0 24.1 24.2 24.3 Van Oevelen et al., 1977
  25. ↑ 25.0 25.1 25.2 Spitaels et al., 2014
  26. ↑ Raj Apte Concepts of sour Beer, 2004
  27. ↑ 27.0 27.1 Martens et al., 1992
  28. ↑ 28.0 28.1 The Beer Temple Interviews #264 with Trevor Rogers of De Garde
  29. ↑ MTF facebook conversation with screenshot of brief De Garde process, March 2014
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