Sour beers have probably been around as long as beer itself. It is remarkable to realize that we only differentiated yeast and bacteria about 150 years ago, which is a drop in the bucket considering the roughly 9,000-year history of brewing. This is not to say that all historical beers were sour: the difference between a sour beer, a Brettanomyces beer, and a Saccharomyces beer are readily apparent and brewers have long known the difference; but without the understanding of what you are dealing with and a microscope to view them, they can be hard to separate.
A quick note before we begin: Brettanomyces is a yeast genus, like Saccharomyces, but it is most often used in conjunction with bacteria for producing sour beers, so that is why I am including it in this chapter. You can brew 100% non-sour beer using Brettanomyces, and many people do, but it is most often used with sours.
You should buy separate plastic fermentation equipment for brewing sour beers (fermentors, buckets, hoses, siphons, and airlocks) to prevent contamination of your regular equipment. This recommendation only applies to equipment that touches the bacteria and is not easily sanitized. Siphon hoses are notorious contamination sources. Stainless steel and glass are easier to aggressively sanitize than plastic, so those are usually not an issue. Be thorough if you don’t want all of your beers becoming contaminated and eventually going sour.
There are four main genera of microorganisms, “the bugs,” commonly used to produce sour beers. These are the bacteria Lactobacillus, Pediococcus, and Acetobacter, and the yeast Brettanomyces. There are a few others, such as Enterobacter, which smells like vomit, but these are not encouraged and usually only encountered in wild fermentations. More microorganisms may be added to the list as time goes on, but for now, these are the main ones.
Lactobacillus is the workhorse of the souring world and is used for making yogurt, sausages, probiotics, and sour beer. There are many different species and strains, but they all produce lactic acid to one degree or another. Lactobacilli bacteria tend to produce a clean sour character, generally soft, tangy, and tart as opposed to sharp, like vinegar (acetic acid), or puckeringly sour, like malic acid. Lactobacilli grow best between 90–115°F (32–46°C), but will still grow well at typical ale fermentation temperatures. Lactobacilli will typically only consume a small amount of sugars in the fermentation, about 2–4 gravity points.1 Lactobacillus species only eat the simple sugars glucose, fructose and maltose; they do not consume maltotriose or raffinose. Most lactobacilli tend to be inhibited by hops and this is one reason that sour beers, such as Berliner weiss, usually only have 5–8 IBUs.
There are several common species of Lactobacillus, some of which are homolactic, meaning that they only produce lactic acid. Other species are heterolactic, meaning they are able to produce lactic acid or ethanol and carbon dioxide. Heterolactic strains do not produce significant amounts of diacetyl.2 The homolactic strains produce more diacetyl, but not as much as yeast or Pediococcus.
Lactobacillus blends and single strains can be purchased from several of the brewing yeast companies, but it is possible to obtain lactobacilli elsewhere as well. Non-fat, “active culture” yogurt is a common source of lactobacilli, as are probiotic supplements sold at pharmacies and grocery stores. The only criticism of these off-the-shelf sources is that single-strain Lactobacillus fermentations are often described as being too clean, or lacking complexity, compared to blends that were developed especially for sour beers. However, probiotic supplement blends of multiple strains are now available and brewers have reported good results with these. The estimated cell count for probiotic supplements is often listed on the package.
The suggested pitching rate for Lactobacillus is between 100 and 200 billion cells per 5 gal. (19 L). Lower pitching rates are said to produce more off-flavors, such as cheese, sweaty feet, and apple juice. Pitching rates are not as critical for sour beers as yeast pitching rates are for regular beers, because attenuation is not the issue. The issue is flavor profile and the length of time it takes for the souring to occur, and this is where another consequence comes into play. Lactobacilli need amino acids to grow; some of these they can synthesize and others must be obtained by breaking down larger proteins present in the wort. In short, all of the popular brewing strains of Lactobacillus will excrete proteolytic enzymes (i.e., enzymes that break down proteins) during the souring process to facilitate their growth, and this can have demonstrable effects on the head retention of sour beers. There are two ways to combat this problem, both of which relate to the pH sensitivity of the proteolytic enzymes, which decrease in activity below a pH of 5 and cease altogether below 4.5. The first method is to use a high pitching rate such that overall growth is reduced and the wort is soured below the pH threshold in a few hours rather than a few days. The second method is to pre-acidify the wort to a pH of 4.5–4.8 to inhibit the enzymes using off-the-shelf lactic acid, then pitching the Lactobacillus culture. The second method is more effective than the first, but the first may seem less like cheating to the brewing purists out there. Kettle souring and other fermentation methods will be discussed later in this chapter.
The following are endpoint pH values that are typically achieved by the various common strains of Lactobacillus during souring:
| Lactobacillus species | Fermentation type | Example endpoint pH |
|---|---|---|
|
L. brevis |
Heterolactic |
3.3 |
|
L. delbrueckii |
Homolactic |
4.4 |
|
L. buchnari |
Heterolactic |
3.8 |
|
L. plantarum |
Heterolactic |
3.2 |
Source: Endpoint pH data averaged from Matthew Humbard, “Beer Microbiology – Lactobacillus pH experiment,” A Ph.D. in Beer (blog), August 5, 2015, http://phdinbeer.com/2015/08/05/beer-microbiology-lactobacillus-ph-expeirment/.
Pediococcus is the other main souring bacteria. It is used for curing sausage and making sauerkraut, in addition to souring beer. Pediococcus differs from Lactobacillus in that it produces lactic acid more slowly, although it tends to sour the beer more (i.e., a comparatively lower pH) than Lactobacillus. Pediococci grow best at warm temperatures, 65–85°F (18–29°C), and will not grow above 95°F (35°C). The recommended pitching rate for pediococci is roughly 10 billion cells per 5 gal. (19 L). Pediococcus is generally resistant to hops and will grow in beers up to 30 IBU.
Pediococcus has two significant fermentation characteristics: it produces a lot of diacetyl and it can make the beer “sick,” as the Belgians describe it. This sickness manifests as polysaccharide gel strands, which is why sick beer is also often described as “ropy.” The polysaccharides are, in fact, beta-glucans that are normally produced by the bacteria as they grow, with more being produced toward the end of growth. These characteristics are the reason why Brettanomyces is often used in collaboration with Pediococcus, because Brettanomyces will clean up the diacetyl and help dissolve the ropy strands.
Even though P. damnosus is stated to be homolactic, Pediococcus in general is said to produce small amounts of acetic acid as well, and this may account for the general opinion that Pediococcus produces a sharper, more complex sour than does Lactobacillus. Perhaps this character actually comes from P. claussenii, which is heterolactic, or perhaps some strains of P. damnosus are actually heterolactic as well. In his book, American Sour Beers, Michael Tonsmeire states,
Many brewers describe the acid character from Pediococcus as being more aggressive and sharp than that from Lactobacillus. This could be due to either the lower pH generated by Pediococcus, or the sub-threshold presence of acetic acid from the Brettanomyces that would not always be found in beers soured with Lactobacillus. (p. 57)
Pediococcus is the primary souring bacteria in Belgian lambic beers, and also in American sour beers, such as those from Russian River Brewing Company.
The following are endpoint pH values that are typically achieved by the various common strains of Pediococcus during souring:
| Pediococcus species | Fermentation type | Example endpoint pH |
|---|---|---|
|
P. damnosus |
Homolactic |
<3.0 |
|
P. claussenii |
Heterolactic |
<3.0 |
Brettanomyces is a genus of yeast that loves to live in wood barrels. Brettanomyces is typically not an acid producer, unless there is a lot of oxygen, in which case it will produce a small amount of acetic acid. It mainly produces “funk,” which are unusual phenolics and esters that contribute aromas and flavors ranging from barnyard and leather, to spice and tropical fruit. Brettanomyces produces amylase enzymes, such as alpha-glucosidase, that allow it to break the bonds in dextrins and other sugars normally considered unfermentable for brewer’s yeast. It also is a strong diacetyl reducer, and some brewers have reported that it breaks down DMS as well. Brettanomyces can add nice complexity to saisons and American sour beers.
There are five species within the Brettanomyces genus: B. anomalus, B. bruxellensis, B. custersianus, B. nanus, and B. naardenensis. The most commonly available types are the B. bruxellensis and B. anomalus. Brettanomyces is a very contrary creature compared to Saccharomyces. It will produce very funky flavors when added in small amounts to a normal Saccharomyces fermentation, but can produce very clean, light bodied, thirst-quenching beers in “100% Brett” fermentations. The pitching rate for 100% Brett fermentations is 1.0–1.25 billion cells per liter, between that of ale and lager pitching rates. Brettanomyces tends to prefer warmer fermentations, between 70°F and 80°F (21–26°C), and ferments slowly. A 100% brett fermentation may take 2–6 weeks to finish. (See cautionary sidebar.)
Brettanomyces is often pitched in conjunction with Pediococcus to clean up the copious diacetyl that Pediococcus produces. For more information on Brettanomyces and the common souring bacteria, you should visit the wiki at Milk The Funk (http://www.milkthefunk.com/wiki).
There are two other readily available sources for bacteria that you can use to make sour beers: malt and the great outdoors. Adding a couple of handfuls of high quality malt to a 1.040 gravity starter works well, if you pre-acidify the starter with a couple of milliliters of 88% lactic acid and purge the head space of oxygen with some carbonated water before affixing the airlock. Detailed instructions are presented below.
The other source is wild yeast and bacteria from the great outdoors. The romanticism of this method may appeal to many brewers, but it is important to understand that you are dipping your net into a dirty pond and hoping to pull out a tasty fish. Many brewers will build a coolship (basically a long shallow open fermentor) and lay their wort out overnight in hopes of getting lucky.
Amazing as it seems, many brewers will trust to luck and prepare themselves to like whatever it is they eventually create, but it doesn’t have to work that way. Instead, you can create a small starter wort and place that outside, let it start, and then smell or taste the result to see if it is something you actually want to brew with. I first heard of this procedure at the 2016 National Homebrewers Conference in Baltimore, Maryland, and it was a head-slapping moment. John Wilson and Brian Wolf presented “Brewing Wild,” in which they described their wild inoculation process and then served us a beer made from it. It was fantastic, and it was simply because the wild yeast starter had been screened before pitching to ensure it was worth brewing with. Simple as that!
John and Brian recommended placing the inoculation wort in a garden or by fruit trees—somewhere out of direct sun where it would have a better chance of picking up a favorable wild yeast (or bacteria). It stands to reason that a garden is a better location than a parking garage. The starter is exposed for a day and night and then brought inside and capped with aluminum foil or an airlock to see what develops.
Step 1: Create a 1.5 L starter of 1.040 gravity wort using 175 g of DME dissolved in 1.5 L of water. Boil it, cover with aluminum foil, and allow it to cool to room temperature.
Step 2: Acidify the wort with 2–3 mL of 88% lactic acid, or about 50 mL of pineapple juice. (Pineapple juice contains citric acid and has a natural acidity of 3.5 pH.) Lowering the pH of the wort to 4.5 will inhibit undesirable and potentially hazardous microorganisms from growing. (See sidebar, “Caution for Wild Fermentations.”) Verify the pH with a calibrated pH meter before continuing. Do not trust pH test strips.
Step 3: Place the wort in an open jar or container where it is likely to pick up favorable microorganisms. You can cover the jar with window screen mesh or a piece of cheesecloth to keep the flies out.
Step 4: After 24 hours bring the wort inside and attach an airlock, or pour it into a flask that can take an airlock. Hopefully the wort will start fermenting within a couple of days. Smell the starter to see if you want to taste it, and taste it to see if you want to brew with it. Good luck!
Step 1: Make an inoculation wort, including acidification, as described above for “Making a Wild Inoculation Wort.”
Step 2: Add two handfuls of fresh Pilsner malt to the jar or flask. Select your malt carefully, it should smell dry and fresh, without any hints of mildew or mold. Old malt may carry a greater variety of microbes than you want to deal with.
Step 3: Top up the flask with carbonated water3 (250–500 mL) to leave only an inch or so (2–3 cm) of head space. The carbonated water will fizz and should purge the headspace of oxygen, reducing the growth of unwanted microbes from the malt.
Step 4: Attach an airlock and let it grow. Lactobacillus grows best at 100–110°F (38–43°C), but it will also grow at room temperature, around 68-77°F (20–25°C). At 110°F (43°C), the growth should be done in about 2–3 days. The gravity of the wort will not significantly change, but the pH will have dropped to between 3.2 and 3.8.
There are three options for brewing a sour beer:
The first option is the more traditional method used by homebrewers for many years and it generally produces a soft complex sour beer over a few months. The souring usually proceeds slowly because there aren’t many residual sugars and carbohydrates left for the bacteria to eat. This is a good method because it’s like the tortoise and the hare—slow and steady will win the race. This method also has the advantage of low maintenance; you set it and forget it. It can take several months to produce a pleasing level of sourness, but it is difficult to over-sour the beer.
The second option involves a method that has traditionally been done as a sour mash, by allowing the mash to sit over a night (or two) to allow the lactic acid bacteria on the malt to proliferate and produce the sour character. The problem with this method is that there is a lot more microbial variety on the malt than just lactobacilli, and you can end up with a variety of stinky fatty acids in the mix, such as butyric acid that smells and tastes like vomit. The popular fix to this problem is kettle souring, where you mash, lauter, and drain to your boil kettle as usual (see chapter 20 for instructions on brewing with grain), and then pitch a prepared bacterial culture to sour it before the yeast fermentation. This method is fast, like 18–36 hours fast, but you need to shoot the rabbit when the race is done. I will lay out the specific steps shortly, but to summarize: you boil the wort briefly to kill any microbes and spores left in the wort from the mash, pitch the prepared bacterial culture, monitor the pH as it drops to about 3.8, then boil the wort (with hops) to stop the souring, and then transfer to your fermentor and pitch the yeast. This method has the advantage of consistency, if it is properly controlled. Many commercial brewers have adopted this method because it allows them to produce a consistent sour product in just a few more days than it takes to do a non-sour fermentation.
The third option, pitching both yeast and bugs together, has been a popular method with homebrewers for several decades, but it can be inconsistent depending on which culture has the higher pitching rate. The brewer’s yeast generally ferments the simple sugars in the normal timeframe, while the slower-growing bacteria “chew on” the remaining carbohydrates after the beer fermentation finishes. The two types of microorganism aren’t really competing for the same resources, because we know the yeast will work much faster on wort simple sugars, but can’t process the complex carbohydrates.
If you do your homework and pay attention to pitching rates and all the fermentation details, you will produce a great sour beer. Many styles are routinely produced this way, but it takes skill. Yeast companies sell several bacteria and yeast blends for styles like Berliner weiss, and Flanders red, just to name a few. You can also (and likely will need to) select and combine your own choices of yeast and bacteria strains to pitch to make your own sour style. Most homebrewers (and commercial brewers) used this method to produce their sour beers until kettle souring came along.
Kettle souring is the compromise between patience and skill, the difference between a pony ride at the state fair and breaking in your own mustang. You still need to hold tight to the reins but there is a clearly marked trail guide to help you arrive at your destination. The following method uses two steps to prevent the growth of unwanted bacteria. The first is a short pre-boil to kill any bacteria and spores that have survived the pasteurizing effects of the mash. The second is pre-acidifying the wort to a pH of 4.5, which will inhibit the growth of Enterobacter and Acetobacter, if you are going to be pitching a mixed culture. If you are going to use a single culture of Lactobacillus, then inhibiting the other bacteria is not an issue.
Step 1. Prepare the culture. You may need to make a starter for your bacterial culture. You can use the inoculation wort starter method described for “Culturing Lactobacilli from Malt” above (but without the grain). Generally, 30–60 mL of yogurt in a 1–2 L starter will be sufficient for a 6 gal. (23 L) batch. If you are using probiotics, then 1–2 capsules into the starter will work as well.
Step 2. Produce your wort. Mash and lauter using your normal methods to produce your wort, and transfer it to your boiling kettle.
Step 3. Short boil. Boil the wort for 10–15 min. to thoroughly sanitize it. Chill the wort to 100–110°F (38–43°C). You can chill to room temperature, but it works more rapidly and more consistently when it’s warm.
Step 4. Pre-acidify. There are two reasons to pre-acidify your wort, (a) because it will help inhibit any unwelcome microorganisms, and (b) because it will inhibit the proteolytic enzymes secreted by the Lactobacillus and thereby preserve your head retention. Acidifying with 88% lactic acid to a pH of 4.5–4.8 should be sufficient. The amount needed will vary but it should be in the neighborhood of 5 mL. Use a pH meter instead of color strips to be sure of an accurate reading. You don’t want to overshoot, or there will be little point in proceeding with your culture!
Step 5. Pitch the bacteria. Pour the bacterial culture starter into the wort and say the magic words.
Step 6. Souring the wort. The wort should take 18–36 hours to sour to a pH of 3.5-ish, depending on the temperature (cooler wort will take longer) and other factors. Measure the pH at least every eight hours to gauge the progress. Taste it as well to judge the sour character and help you decide when it is sour enough. You are looking for a pH of 3.2–3.8, depending on the type of bugs you are pitching. A pure Lactobacillus culture has a soft acidity, and a lower pH toward 3.2 seems to taste best. In mixed cultures, such as those grown from the grain, the mix of acids is more biting and a higher pH toward 3.8 tastes best.
Step 7: Boil and ferment the wort. After the wort has soured to the desired level, boil it with your hops (according to the recipe), then chill, aerate, and pitch your yeast as you normally would. You should experience a normal fermentation and decrease in gravity. In addition, the pitching rate for the yeast fermentation should be higher than normal. Therefore, for ales that would normally pitch 0.75 billion cells per liter per 4 gravity points (or 0.75 billion/L/°P; see chapter 7) you would instead pitch 1.0 billion cells. Brewers report that European ale strains seem to be more acid tolerant than American ale strains and are better able to fully attenuate under these conditions.
The following three recipes cover a few European styles and an American sour ale. The fermentation temperatures given for these recipes are general recommendations. Check the yeast or bacteria supplier’s packaging for specific temperature recommendations. Kettle souring for extract versions should be done before boiling with hops. Procedure: Boil wort A for 15 minutes without hops, conduct the kettle sour procedure, then boil with hops according to recipe, add wort B, then chill and ferment as usual.
Die Weiße Königin
Berliner Weisse
|
All-Grain Version |
||
| Grain bill | Gravity points | |
|---|---|---|
|
3.3 lb. (1.5 kg) wheat malt |
14 |
|
|
3.3 lb. (1.5 kg) Pilsner malt |
13 |
|
|
Boil gravity for 7 gal. |
1.027 |
|
| Mash schedule | Rest temp. | Rest time |
|
Conversion rest – Infusion |
150°F (65°C) |
60 min. |
| Hop schedule | Boil time | IBUs |
|
0.35 oz. (10 g) Hersbrucker 4% AA |
60 min. |
5 |
| Microbe strain | Pitch (billions of cells) | Fermentation temp. |
|
Kettle sour with Lactobacillus |
150 |
104°F (40°C) |
|
German ale or Kölsch yeast |
175 |
65°F (18°C) |
| Recommended Water Profile (ppm) |
Brew cube: Pale, Balanced, Soft |
||||
|---|---|---|---|---|---|
|
Ca 50–100 |
Mg 10 |
Total alk. 0–50 |
SO4 0–50 |
Cl 50–100 |
RA −50–0 |
Oud Geestigbier
Belgian Witbier
|
All-Grain Version |
||
| Mashing option | Gravity points | |
|---|---|---|
|
5 lb. (3.2 kg) Pilsner malt |
20 |
|
|
5 lb. (3.2 kg) wheat malt |
21 |
|
|
1.1 lb. (500 g) flaked oats |
4 |
|
|
~1.75 oz. (50 g) orange peel – Steep 15 min. |
||
|
~0.5 oz. (15 g) crushed coriander seed – Steep 15 min. |
||
|
0.1 oz. (3 g) dried chamomile flower – Steep 15 min. |
||
|
Boil gravity for 7 gal. |
1.045 |
|
| Mash schedule | Rest temp. | Rest time |
|
Conversion rest – Infusion |
153°F (67°C) |
60 min. |
| Hop schedule | Boil time | IBUs |
|
0.6 oz. (17g) Mandarina Bavaria 8% AA |
60 min. |
15 |
| Microbe strain | Pitch (billions of cells) | Fermentation temp. |
|
Kettle sour with Lactobacillus |
150 |
104°F (40°C) |
|
Belgian witbier or Kölsch yeast |
275 |
68°F (20°C) |
| Recommended Water Profile (ppm) |
Brew cube: Pale, Malty, Soft |
||||
|---|---|---|---|---|---|
|
Ca 50–100 |
Mg 10 |
Total alk. 0–50 |
SO4 0–50 |
Cl 50–100 |
RA −100–0 |
Notes
1. Any bittering hop will work, the goal is 15 IBU of clean bitterness. Mandarina Bavaria has a nice orange or tangerine character that blends well with this style.
2. Wash two medium-sized oranges and use a vegetable or apple peeler to carefully remove the outer rind. This should be about 50 g total. Do not peel too deeply—the peel should be thin, bright orange, and without white pith.
3. After the boil, turn the heat off and place the orange peel, crushed coriander, and chamomile in a mesh bag and allow them to hot steep for 15 min. before chilling. They should be removed before fermentation. Additional spices (same proportions) can be cold steeped after fermentation for extra aroma, if desired.
Sour Bastard
American Sour Ale
|
Extract and Steeping Grain Version |
||
| Wort A | Gravity points | |
|---|---|---|
|
3.5 lb. (1.6 kg) pale ale DME |
53 |
|
|
1.0 lb. (450 g) Weyermann Caraaroma® malt – Steeped |
3 |
|
|
0.5 lb. (225 g) Briess Victory malt – Steeped |
3 |
|
|
Boil gravity for 3 gal. |
1.059 |
|
| Hop schedule | Boil time | IBUs |
|
0.9 oz. (25 g) Centennial 10.5% AA |
60 min. |
25 |
| Microbe strain | Pitch (billions of cells) | Fermentation temp. |
|
Kettle sour with mixed* culture |
250 |
104°F (40°C) |
|
German ale or Kölsch yeast |
350 |
65°F (18°C) |
|
Brettanomyces bruxellensis yeast |
200 |
65°F (18°C) |
| Wort B | Gravity points | |
|
4.5 lb. (2.04 kg) pale ale DME |
67.5 |
|
| Recommended Water Profile (ppm) |
Brew cube: Amber, Balanced, Medium |
||||
|---|---|---|---|---|---|
|
Ca 75–125 |
Mg 20 |
Total alk. 75–125 |
SO4 100–200 |
Cl 100–150 |
RA 0–50 |
Notes
* You can use a mixed souring culture, such as Wyeast’s Roeselare Blend (3763) or Whitelab’s Belgian Sour Mix 1 (WLP655), and pitch all at the same time, or you can kettle sour. If kettle souring, you can grow your own pediococci/lactobacilli blend from an inoculation starter, or you can use two specific strains of Pediococcus and Lactobacillus.
Cherry juice option: You can make this a nice sour cherry beer by adding 1.5 lb. (680 g) of cherries, or 0.5 L of sour cherry juice concentrate (68°Brix, 31 PPG [259 PKL]) after the second day of yeast fermentation. This equates to about 0.5 lb./gal. (60 g/L) of cherry puree.
1 Elke Arendt, presentation, Belgian Brewing Conference, KU Leuven, Belgium, September 2015.
2 Matthew Humbard, “Physiology of Flavors in Beer – Lactobacillus Species,” A Ph.D in Beer (blog), April 13, 2015, phdinbeer.com/2015/04/13/physiology-of-flavors-in-beer-lactobacillus-species/.
3 This advice taken from Derek Springer, “Lactobacillus Starter Guide,” Five Blades Brewing, April 19, 2015, http://www.fivebladesbrewing.com/lactobacillus-starter-guide.