Lactobacillus Beer - Brewing With Lactic Acid Bacteria
By Dr. Brian A. Nummer
Usually considered an unwanted infectious pest in the brewhouse, lactic acid bacteria can be harnessed as an exquisite ingredient for selected beer styles.
Since the days of Pasteur, lactic acid bacteria have been scorned, living at the periphery of civilized brewing society under the label “spoilage organisms.” Few brewers purposely invite these bacteria into their breweries to aid in the fermentation of their wort. In fact, most brewers take special care to eradicate any possibility of bacterial growth. Yet, several beer styles from Belgium and Germany are made using these bacteria to produce a tasty, characteristic sourness. Can these bacteria be all bad?
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Lactics in Beer
The percentage of acids, primarily lactic and acetic, in a particular beer determines its sourness. Some beers have just a hint of tartness; others are overpoweringly sour. German Berliner Weisse and several Belgian beer styles are characterized by their sourness. Each style has a different level of sourness, and even within the same beer style this level varies. Fermentation with lactic acid bacteria is not an exact science, and one brand of beer may have different levels of sourness from batch to batch or from year to year.
Examples from Germany: German Berliner Weisse originated in Berlin and Bremen, Germany. A wheat beer made from 30–60% malted wheat, Berliner Weisse is produced using one of two different processes. In the traditional process, unboiled wort is fermented with a mixture of Brettanomyces ale yeast and heterofermentative lactic acid bacteria. After the main fermentation, the beer is blended with kräusen and bottled. Secondary fermentation and maturation then take place in the bottle for up to two years. A commercial example of this style is Berliner Schultheiss. This style is characterized by an intense, vinegary sourness, caused by lactic and acetic acids, which is complemented by an ester fruitiness from Brettanomyces.
A contemporary process (frowned upon by traditionalists) for making Weissebier was developed probably as a response to the unpredictability involved in brewing sour beers. Compared to traditional Berliner Weisse, this modern version is less sour, presenting only lactic acid and no esters. In the contemporary process, the starting gravity is low, at 7–8 °P (O.G. 1.028–1.033). The wort is split in half; one half is inoculated with homofermentative Lactobacillus sp. and the other half with ale yeast (Saccharomyces cerevisiae). Each is kept in a separate vessel and allowed to ferment at 59–77 °F (15–25 °C) for four weeks or more. After fermentation, the two parts are blended, filtered, and transferred for secondary storage at 41–50 °F (5–10 °C) for 13 months. The beer is bottled with a fresh addition of kräusen that includes yeast (no lactic acid bacteria). Once refermented in the bottle, the beer is ready to consume. A commercial example of this style is Berliner Kindl Weiss. Both of these beers are often served with sweetened raspberry or woodruff syrups to balance the acidity.
Examples from Belgium: Belgian sour beers include Iambics, witbiers, and Flanders styles. Lambic beers are spontaneously fermented wheat beers from the Brabant and Brussels regions of Belgium. Lambics provide a fascinating field of exploration for the inquisitive microbiologist.
Lambics: Lambic fermentation involves a complex sequence in which yeast strains and bacteria pass into and out of active phases. After cooling the wort, yeast and bacteria are allowed to “fall” into the open fermentors. Certain bacteria and the yeast Klockera, the most competitive, thrive for 2–3 weeks. Species of Saccharomyces then perform the main alcohol fermentation for 3–4 months. After that, lactic acid bacteria, dominated by Pediococcus damnosus, provide lactic acid fermentation for 4–5 months. This is followed by the Iambic yeasts of the genus Brettanomyces. Pediococcus bacteria and Brettanomyces yeasts ferment the complex sugars left behind by the other species. Several other bacteria and yeasts play minor roles. The process is a dynamic ebb and flow of activity from all of these various agents, each one present from the beginning of fermentation but becoming active only when conditions become favorable thanks to changes in pH and other factors resulting from another agent’s activity. The result is the wonderfully complex blend of flavors of Iambic beer. For a detailed look at Iambics, consult Jean-Xavier Guinard’s book, Lambic Beer. For brewing Iambics, he recommends the addition of three important cultures: an ale yeast, followed by Pediococcus damnosus and Brettanomyces.
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| The Lactic Family |
| Lactic acid bacteria are Gram-positive, non–spore-forming rods (or cocci), and they are obligate fermenters. An obligate fermenter is a microorganism that must ferment a carbohydrate source. They do not grow aerobically. Lactic acid bacteria include Lactobacilli and Pediococci. Pediococci are microaerophilic; that is, they prefer an atmosphere with low oxygen levels. They grow poorly or not at all in air. The small rods often appear in groups of four (tetrads). In the past, Pediococcus was categorized as a beer sarcina (a term that included the anaerobic lactic-acid, beer-spoilage organism sarcinia). The most important species to brewers is Pediococcus damnosus, formerly called P. cerevisiae. The taxonomy has again changed, and this organism is now classified as P. acidilactici. Lactobacilli are facultative anaerobes — they can ferment in the presence or absence of air, but prefer reduced oxygen levels. Lactobacilli are also rod-shaped. One important species to brewers is Lactobacillus delbrückii. The species name delbrückii came from Max Delbrück, a founding father of microbiology, who characterized bacteria in the sour beers of Berlin (Berliner Weisse). Besides L. delbrückii, several other Lactobacilli find their way into beer, including L. brevis, L. acidophilus, and L. lactis. Some lactic acid bacteria produce diacetyl in quantities high enough to contribute to the flavor and aroma profile of the beer. Diacetyl is associated with a buttery or butterscotch flavor. In some beers this flavor in unacceptable, but for some others it is desired. Diacetyl is produced from the decarboxylation of acetolactate. Presumably, high levels of acetolactate are attributable to high levels of lactate, an ester of lactic acid present in lactic acid bacteria fermentations. Diacetyl has a taste threshold of 100–140 mg/L. Pediococci usually produce levels above the threshold, whereas Lactobacilli produce levels just below the threshold (Table I). Some lactic acid bacteria produce dextrans (long polymers of glucose). Dextrans can cover the surface of wort or beer, or form “ropes.” They are visually unappealing, but otherwise harmless, and they can also be useful in protecting against oxidation. Pediococci can produce a diffuse dextran on the surface that can appear shiny. The dextran is easily mixed back into the beer, but will reappear a short time later. In mixed-culture fermentations, the other cultures present will break down these dextrans. Some wild yeasts produce dextrans of their own. Lactic acid bacteria are divided into two categories based on their by-products of fermentation. The homofermentative group produces primarily lactic acid, whereas the heterofermentative group produces lactic acid, acetic acid, ethanol, and carbon dioxide. Either group will cause spoilage in beers in which the bacterial by-products are not desired. The homofermentative Lactobacilli and Pediococci and heterofermentative Lactobacilli each have different flavor profiles. The homofermentative Lactobacilli produce almost exclusively lactic acid. Pediococci are also homofermentative, but they also produce diacetyl, adding a buttery flavor. Last, the heterofermentative Lactobacilli produce both lactic and acetic acids (Table I). |
| Table I: Characteristics of Beer Worts Fermented by Various Cultures* | |||||
| Culture | Ethyl Acetate (mg/L) | Acetic Acid (mg/L) | Lactic Acid (mg/L) | Diacetyl (μg/l) | |
| DL-lactic acid added to beer | 18 | 95 | 370 | 12 | |
| P. damnosus | 22 | 90 | 420 | 150 | |
| L. brevis (heterofermentive) | 24 | 250 | 370 | 90 | |
| L. brevis and P. damnosus | 22 | 595 | 490 | 140 | |
| S. cerevisiae and P. damnosus | 24 | 85 | 460 | 120 | |
| S. cerevisiae and L. brevis | 24 | 520 | 410 | 90 | |
| S. cerevisiae, P. damnosus, and L. brevis | 23 | 360 | 490 | 110 | |
| S. cerevisiae | 18 | 80 | 150 | 25 | |
| * Source: Reference 4. | |||||
Witbier: Witbier is a tart, dry, acidic wheat beer from the Brabant region of Belgium. It is traditionally made from wheat malt and flour, barley malt, and oat flour. Perhaps the most famous witbier is Hoegaarden Wit from the town of the same name.
Traditionally, witbiers were intensely sour. Over the years, they have mellowed, probably in response to consumer preferences. Witbiers are often fermented with lactic acid bacteria and brewing yeast mixtures. Wort for Celis Wit is said to be first pitched with Lactobacillus. The process is arrested at a pH of 4.4 (presumably by filtration), and then yeast is added.
Flanders styles: Flanders-style beers are definitely the most eclectic of the sour beers. They range from brown to red in color and are characterized by a distinct sourness caused by both lactic and acetic acids. Most of the breweries making this style produce several beers from a single wort by blending, diluting, or adding fruit. Two extremes within this style are brown beers such as Liefmans (Brouwerij Liefmans, Oudenaarde, Belgium) and red beers such as Rodenbach (Brouwerij Rodenbach, Roeselare, Belgium).
Liefmans brown beer, from East Flanders, is brewed with Pilsener and caramel malts and boiled for what was once an all-night-long simmer but today is a standard 90–120 minute boil. (Unverified sources suggest the overnight boil was due to inferior equipment and not to brewing eccentricities.) The result is a brown-hued wort of original gravity 1.048. The brewery’s select culture of yeast is said to contain lactic acid bacteria. Liefmans is fermented and aged in stainless steel for up to a year. The beer is filtered, blended, pasteurized, and sweetened before force-carbonation and bottling.
| All-Grain Wort-Souring Recipe |
| Sour Wort Witbier (Makes 5 gallons) Ingredients 3 lb Pale malt 3 lb Wheat malt 2 lb Flaked wheat ½ lb Oat flakes Saaz hops (or other Noble hop), 10–15 IBUs ½ oz Coriander ½ oz Curaçao orange peel LactoCapsules (Head Start, Aeonbräu, Athens, Georgia), or Lactobacillus culture Witbier yeast 3 oz Corn sugar Original gravity = 1.048 Final gravity = 1.009 Procedure Combine malt grists and grain flakes with strike water to achieve 122 °F (50 °C). Rest 30 minutes. Raise the temperature to 149 °F (65 °C) for 45 minutes, to 158 °F (70 °C) for 15 minutes, and to 176 °F (80 °C) for mash-out. Lauter as usual, and expect a starch haze. Add hops and boil for 60 minutes. Add bitter (Curaçao) orange peel and boil for 15 minutes. Add crushed coriander seeds and boil for the remaining 15 minutes. Cool. Inoculate with the contents of two LactoCapsules or with an 8 oz starter of homofermentative Lactobacillus. Allow the wort to sour at the temperature recommended for the lactic acid culture. When desired sourness is achieved, boil the wort for 10 minutes to kill the lactic acid bacteria. Cool. Add a starter culture of witbier yeast. Allow to ferment at 64–75 °F (18–24 °C) for one week. Age at 53–59 °F (12–15 °C ) for three weeks or more. Bottle with 3 oz corn sugar for priming (or 1 tsp/12 oz bottle). Condition as usual. |
Rodenbach’s red beer, from West Flanders, is brewed with several varieties of malt and corn grits to achieve an original gravity of 1.045. The red color derives from Vienna malts and oak barrel tannins. The beer is fermented with a mixture of yeasts, then aged in wooden casks for up to two years. Hidden in the cracks of the wood in these casks are lactic and acetic acid bacteria. The resident bacteria, in small numbers, provide acid fermentation over time. For some people, the resulting sourness is too intense; for these people, the brewery makes Alexander, a filtered, sweetened version.
Lactic Acid Bacteria in the Brewhouse
Lactic acid bacteria provide a versatile tool for producing acid beers. Bearing in mind the need to isolate your lactic acid bacteria from standard fermentation yeasts — where lactic infections can be most unwelcome — several methods can be used to enhance certain beers with the sourness characteristic of lactic fermentations. (See the box, “The Lactic Family,” for a review of the flavor and fermentation characteristics of various lactic strains.)
| Malt Extract Split-Fermentation Recipe |
| Berliner Weibe (makes 5 gallons) Ingredients 3 1/3 lb Wheat malt extract ¾ lb Light dry malt extract Saaz hops, 6 IBUs Lactobacillus delbrückii, or other homofermentative Lactobacillus Berliner Weisse ale yeast 3oz Corn sugar Original gravity = 1.030 Final gravity = 1.006 Procedure Boil hops for 60 minutes in wort prepared from the extracts following typical brewing procedures. Typically Berliner Kindl Weisse is split 50:50. Split the wort in these proportions into two clean, sterile vessels. Inoculate the lactic wort with Lactobacillus. Ferment 2–3 weeks at 98 °F (37 °C) for Lactobacillus delbrückii or at optimal temperature for the culture being used. Ferment the remaining wort with Weissebier ale yeast at 59–77 °F (15–25 °C) for 2–3 weeks. Boil the lactic-fermented wort for 10 minutes to kill the lactic acid bacteria. This boiling step can be skipped, but live lactic acid bacteria will result in constant flavor changes as the beer ages. (The Berliner Kindl Brewery filters out the lactic acid bacteria.) Cool and combine this wort with the ale yeast-fermented wort. Transfer to the secondary and, if possible, store cool at 50 °F (10 °C) for one month or more. Bottle with 3 oz corn sugar for priming (or 1 tsp/12 oz bottle). Condition as usual. Drink as is, or add sweet fruit syrup, as desired. |
In pure cultures of sufficient biomass and at the optimal temperature for each culture, acid production is usually rapid. In worts fermented with both a lactic acid bacteria and a yeast culture, however, acid production is slower; both compete for the wort sugars, and yeast are typically much more prolific. If the lactic acid bacteria are added to the secondary — by which time all of the simple sugars have been used — they must scavenge for complex sugars, some of which they ferment through a slow process of acid production. This is the case in Iambics, where lactic acid bacteria proliferate only after most of the wort sugars have been used. It can therefore take many months to produce lactic or acetic acids at flavor threshold levels.
In addition, lactic acid bacteria are sensitive to hop acids and tannins. Hop acids are bacteriostatic, exhibiting a growth-restricting effect on many bacteria. Typically, Pediococci are less resistant to hop acids than are Lactobacilli. Experiments suggest that this feature is very strain-dependent. If a culture is very hop-acid sensitive, the methods used to acidify the wort must be altered to allow the lactic culture to ferment in a hop acid–free wort (ferment hopped and unhopped worts separately and then blend).
| Malt Extract Mixed-Fermentation Recipe |
| Me Mumm’s Sweet and Sour Stout (makes 5 gallons) It is rumored that Guinness includes a portion of lactic- and acetic-fermented wort in its stout, possibly to duplicate the historical contamination of the beer casks with Brettanomyces yeasts. I discovered another stout called Mumme in Vienna, Austria, patterned after the original stouts of the 1500s in Braunschweig, Germany. Yes, stout actually originated in Germany. This stout was marvelously sweet and sour. I was overwhelmed. Within minutes, I planned a recipe to duplicate this beer. Ingredients 3 1/3 lb Stout-flavored malt extract 3 1/3 lb Wheat malt extract 1 oz Hallertauer hop plugs for aroma Flanders lactic culture (Head Start #320L; a heterofermentative culture that will produce both lactic and acetic acid, an essential component of the recipe). A suitable stout yeast or a Lactobacillus and Pediococcus mixture (I use Head Start #190 SnP) 8oz Lactose 3oz 3 oz |