Sour beer

Sour beer contains lactic acid, which normally comes from bacteria. In this article we focus on modern methods of managing the yeast and bacteria, which allows us to brew consistent, high-quality sour beer on a rapid timeline. Making sour beer doesn't need to be complicated or require long periods of aging!

Of all the Lactobacillus (Lacto) species, Lactobacillus plantarum has been a game-changer for making sour beer. It adds a nice flavor, it quickly produces a robust sourness at room temperature, and it's extremely hop-sensitive, all of which we can use to our advantage. This species of bacteria is the key to these modern methods because it can sour along with the yeast fermentation rather than requiring a separate or prolonged souring phase.

Similarly, modern isolated Brettanomyces (Brett) cultures combined with modern pitching strategies allow us to produce wonderful funky sour beer in the same time it takes to produce a normal ale! Additionally these methods are fully compatible with low oxygen brewing, which enables the creation of beers with a unique amazing flavor unlike any that the world has ever experienced.

Lactobacillus plantarum

This is only species of bacteria that works with these modern souring methods.

Sources

Several sources of L. plantarum are readily available in the US:

• Swanson's L. plantarum capsules - on Amazon.
• GoodBelly liquid - in stores, capsules are on Amazon
• Renew Life Ultimate Flora - in grocery and drug stores like Walmart
• Lallemand WildBrew Sour Pitch - from The Beverage People, for example
• Other yeast labs sell Lacto blends of L. plantarum mixed with other species, often L. brevis. Examples include OYL-605 and TYB Lacto blend. These blends are not ideal for use with these methods because they are more hop-tolerant.

Important: Store the Lacto in the refrigerator, and check the expiration date before use.

Lacto flavor and souring

Generally the Lacto contributes complementary flavors such as a nice lemony citrus tartness, with other notes such as berry, melon, peach, yogurt, smoke, and/or some slight earthy funk. Most of the desirable flavor from bacteria is expressed within a few days. There will be a bit more "complexity" that develops over the course of a couple weeks if you don't add hops before then, and the extra complexity may or may not be desirable to you. If Brett is present, it often metabolizes anything that might be undesirable such as isovaleric acid.

Although the majority of souring occurs within a couple days, the Lacto may continue to sour up until about 1-2 weeks if no hops are added (using basic souring methods). However, its ability to produce acid is self-limiting. Normally this species stops producing acid when the pH drops to around 3.1 to 3.3.

Modern Fast Souring

These methods are great for beginners and also more experienced brewers. The brewing process is basically the same as normal, except we add Lactobacillus plantarum to produce the sourness. These methods allow the production of beer within a normal time-frame for ales.

It is extremely important to not add any hops before adding the Lacto because hops will prevent souring. This includes using yeast cake from a batch that had hops.

Lactobacillus plantarum will not contaminate your other beer or "ruin" your equipment. Normal cleaning and sanitation procedures easily remove L. plantarum. It is extremely hop-sensitive and therefore is incapable of souring your clean beers with hops, even if you were to directly add it. These techniques actually have LESS risk overall of contamination compared to kettle souring!

Co-sour method

This method is super easy and produces great results. Yeast and bacteria are pitched at the same time, hence the name.

1. Make unhopped wort. Boiling is optional but recommended.
2. Chill, transfer to fermenter, and aerate as normal.
3. Pitch both the yeast and Lactobacillus plantarum.
4. Ferment as normal, at 65°F (18°C) or higher.
5. Optional/recommended: Add hops when it reaches the desired sourness. (Dry hops or hop tea)
6. Package as normal.

A starter for the Lacto is not needed because Lacto pitch rate isn't particularly important for co-souring. For a 5 US gal (20L) batch, you only need to pitch 1-2 probiotic capsules or a few ounces of GoodBelly.

Post-sour method

This method is designed to maximize yeast flavor, but it's slightly more complicated than the co-sour method. The basis behind this method is that acidity mutes yeast expression. Therefore we delay adding the souring bacteria until the yeast produce most/all of their flavor, which occurs in the first 30-50% of fermentation. This is a great method to use with a fruity yeast strain. It is so named because the bacteria are pitched after the yeast.

1. Make unhopped wort. Boiling is optional but recommended.
2. Chill, transfer to fermenter, and aerate as normal.
3. Optional/recommended: Drain some of the wort into a sanitized container to make a starter for the Lactobacillus. (See Lacto starter)
4. Pitch the yeast.
5. Ferment as normal, at 65°F (18°C) or higher.
6. When the fermentation is around 20-40% complete (typically around 24 hours after pitch), add the Lactobacillus plantarum culture (but not the layer of calcium carbonate if you made a starter).
7. Optional/recommended: Add hops when it reaches the desired sourness. (Dry hops or hop tea)
8. Package as normal.

Comparison with other souring methods

The kettle souring method is a relic from when brewers were sour mashing or using wild microbes (e.g. a handful of grain) for souring wort. In that case it made sense to kill the wild culture because there could be undesirable bacteria and/or yeast species that would cause problems later on. Nowadays there is no need for the separate souring step — it has downsides but no upsides.

More recently, a very small number of yeast strains have become available that produce lactic acid. (See Lactic acid yeast.) Given that there's not any tangible benefits to using these strains, there's not much reason to do so. Lacto souring methods are easy and much more flexible.

Other alternative souring methods are to add straight lactic acid, or use high amounts of acidulated malt. Subjectively these methods are less likely to make a "quality" beer, and so they won't be discussed here.

Characteristic	Co-souring	Post-souring	Pre-souring (kettle sour)	Lactic Acid Yeast
Brewing Process	Easy/Normal	Normal-ish	Extended and more complicated: Requires two separate brew days Requires sealing brew kettle Pre-acidification recommended pH monitoring recommended	Normal
Turnaround Time	Normal	Normal	Extended by a day or more	Normal
Recommended Yeast Pitch Rate	Normal	Normal	Higher pitch rate recommended	Normal
Recommended Bacteria Pitch Rate	Low	High	Very high	N/A
Able to control hop rate?
Able to control sourness?
Avoids high contamination risk?
Allows yeast flavor expression?				(Limited selection)
Probiotic bacteria survive?
Desirable bacteria flavor?
Allows low oxygen brewing?
Specific bacteria species required?	Yes	Yes	No, if you can control temp	No bacteria required

Modern Fast & Funky Souring

Brettanomyces yeast takes sour beers to the next level by creating a complex and unique blend of fruity and funky flavors. With modern methods, these so-called "funky" sour beers with Brett can be produced on a rapid timeline similar to any ale. In a nutshell, this method is a post-sour, with highly fermentable wort pitched with both Sacc and Brett from a starter. This process is designed to maximize flavor from both the Sacc and Brett, produce a good sourness quickly, and also reach full attenuation quickly so it can be packaged.

1. Make unhopped wort. Boiling is optional but recommended.
2. Optional/recommended: Make the wort highly fermentable.
   • Minimize or eliminate the use of crystal malts and unmalted adjuncts.
   • Target OG about 1.040 to keep ABV relatively low (around 5%).
   • Mash around 149°F (65°C) for 2 hours. If step mashing, include a couple of long beta rests.
3. Chill, transfer to fermenter, and aerate as normal.
4. Optional/recommended: Drain some of the wort into a sanitized container to make a starter for the Lactobacillus. (See Lacto starter)
5. Pitch both Saccharomyces and Brettanomyces yeast. For best results, a starter for the Brett is required. (See Brett starter)
6. Add glucoamylase enzyme per product instructions.
7. Ferment as normal, at 65°F (18°C) or higher.
8. When the fermentation is around 20-40% complete (typically around 24 hours after pitch), add the Lactobacillus plantarum culture (but not the layer of calcium carbonate if you made a starter).
9. Optional/recommended: Add hops when it reaches the desired sourness. (Dry hops or hop tea)
10. Package as normal.

At the time of packaging, the beer should have tons of flavor from all the ingredients, including the Brett. However, the flavor from the Brett will be mainly fruit-forward. Additional aging (at room temp or possibly cellar temp) may bring out more of the funky character from the Brett, depending on the strain. We do not recommend aging in the fermenter because THP formation may be more likely and the risk of oxidation is increased.

Caution:
Using Brettanomyces yeast carries some risk of contaminating future beers if you do not use proper cleaning methods. However, many brewers successfully use the same equipment for both "clean" beers and mixed fermentation sours with Brett. (See Contamination)

Additional techniques

These processes can help improve your beer, make it unique, and adjust it to your own taste.

Lactobacillus starter

1. The starter volume only needs to be roughly 1% of the batch volume, so about 200 mL for a 5 US gallon (20L) batch. Larger is fine too.
2. Add 20 g/L calcium carbonate (e.g. 4 grams in a 200mL starter).
3. Add Lactobacillus plantarum to the starter. Only a small amount is needed (e.g. the contents of one probiotic capsule).
4. Cover and let sit somewhere between 68–98°F (20–37°C).
5. Swirl it occasionally. Try to mix in the calcium carbonate.

Rationale for the calcium carbonate:
Lacto growth is inhibited by low/acidic pH. Calcium carbonate (a base) neutralizes the lactic acid and thereby helps maintain a high pH, increasing growth and yielding a much higher cell count.

The Lacto does not form a krausen like yeast does, but you may see some slight bubbling caused by the acid-base reaction.

Brettanomyces starter

Making a starter for Brettanomyces is similar to making a starter for Saccharomyces, except it needs to ferment longer and stirring is not as important. The starter should be prepared one week before brewing your Fast & Funky Sour.

Recommended process (on a stir plate):

1. Use 100mL starter per gallon of batch volume (e.g. 500mL for a 5 gallon batch). Using an Erlenmeyer flask is recommended.
   • Add 100g/L light DME (or use 1.036–1.040 wort).
   • Optional: Add 2 g/L yeast nutrient, ideally with amino acids and vitamins.
   • Optional: Add 1 drop of foam control.
2. Bring to a boil and then remove from the heat. Add the stir bar.
3. Chill in an ice bath or cover with foil and allow to cool.
4. Aerate thoroughly (by shaking or stirring on the stir plate).
5. Add the Brettanomyces culture.
6. Cover loosely with foil and set the stir plate on a low speed, just enough to keep it moving.
7. Allow to ferment for about a week. If possible, control temperature to about 77°F (25°C).

If you don't have a stir plate, that's fine, just swirl it often.

Using multiple "steps" (a series of starters) is not recommended because of possible THP formation.

Adding Brett at bottling

The "Fast & Funky Souring" method above is fully compatible with adding additional Brettanomyces at bottling. You may use isolated Brett strains or blends, mixed Brett/bacteria cultures, or bottle dreg cultures. It can be as simple as adding a few drops of slurry from a yeast bank to bottles. You can create a large variety of beers from a single batch this way. For example with only 3 Brett cultures you can make 8 different beers from one batch. Funky character from the bottling stains typically becomes apparent within 2 months but starts to peak around 3–6 months.

For beers produced with any other methods, adding Brett at bottling is NOT recommended because additional fermentation is possible, and would result in over-carbonation (gushing or explosion).

Controlling the sourness

Decreasing sourness is pretty straightforward:

• Pitch less Lacto.
• Ferment cool, closer to 60°F (16°C).
• Add hops when it reaches your preferred level of sourness (or TA or pH).

Increasing sourness is perhaps a little more tricky:

• Pitch more Lacto.
• Pitch the Lacto early (at the expense of yeast flavor).
• Don't add hops at all, or wait at least 1–2 weeks after pitching the Lacto before adding hops.
• Increase the carbonate/bicarbonate in your brewing water (yes, higher alkalinity). It might be beneficial to add calcium lactate or calcium carbonate directly to the fermenter; this is somewhat untested but results have been promising.
• Consider adding acetic acid, which can increase the perceived sharpness of the sour taste. (See below)

Adding acidic complexity

Many commercial "traditional" sour beers contain significant amounts of acetic acid. Acetic acid (vinegar) can add a nice tangy flavor and increase the complexity of the acid profile. This is easy to duplicate. You may simply add acetic acid, such as a commercial malt vinegar, or homemade vinegar that you've produced. (See Vinegar production)

With a 5% vinegar, adding 6–12 mL per liter of beer (23–45 mL vinegar per gallon) will produce 0.3–0.6 g/L acetic acid in the beer, the generally desirable range for a nuance of complexity. A bench trial is also a good option to determine the right amount for your taste, especially if you make your own vinegar. Also if using your own vinegar, you can do an acid titration to determine the concentration of acetic acid and thereby add a known quantity, which may be helpful for future reference.

Recipes

(In progress)

Ingredient suggestions

Yeast
There are many very flavorful yeast strains that can make amazingly fruity beer using a post-sour method.

Saccharomyces

• White Labs 644 Saccharomyces "Bruxellensis" Trois - Tropical, pineapple, mango, stone fruit - 70–85°F
• Omega Voss Kveik OYL-061 - Fresh orange and orange marmalade - 72–98°F (22–37°C)

Brettanomyces

• Wyeast 5526 Brettanomyces Lambicus - Cherry pie, horse blanket funk - 60–75°F

Bacteria
It is currently unknown how different bacterial cultures compare in terms of flavor. However, a blend of species such as Renew Life Ultimate Flora possibly adds a more complex flavor as opposed to a single strain.

Malt
Malt can obviously add plenty of flavor — Flanders Red is a good example of a traditional malty sour. The only limit is your imagination.

For a malty sour, consider using an amber/red ale or brown ale grain bill. Smoked malt is another thing to consider, such as a rarely seen Lichtenhainer (basically a smoked Berliner Weisse). There's also the option to include some dark Belgian candi syrup in something like a sour Belgian Dubble.

Hops:
Hoppy sours can be quite good. Fruity hops are a good choice, as well as Noble hops. Here are a few suggestions in no particular order:

• Amarillo - citrus (orange, lemon, grapefruit), floral, tropical
• Southern Passion - Passion fruit, guava, red berries, melon, grapefruit, floral
• Idaho Gem - Pineapple, cherry, herbal, spicy, candied fruit
• El Dorado - Tropical, fruity, cherry, mango, sweet
• Callista - Citrus, stone fruit, passion fruit, red berries, gooseberry
• Czech Saaz - Floral, citrus, spicy, herbal
• Strisselspalt - Spicy, citrus, floral, fruity, herbal

Anecdotally, anywhere from 0.5 to 1 oz per 5 gallons (15-30 g per 20 L) adds a nice hop character and prevents further souring. Hops do not kill the Lacto, they only stop growth and metabolism.

Water
Here's what we generally recommend for water:

• 30–100 ppm calcium
• 50–100 ppm chloride (higher for Gose)
• 0–50 ppm sulfate
• 0–50 ppm sodium (higher for Gose)
• 10–30 ppm magnesium
• Mash pH and kettle pH should be targeted to your preferred values, generally around 5.4 and 5.1 respectively.

Chloride adds perceived body and accentuates sweetness. Sodium enhances flavor and can also add a fullness to the beer. Magnesium is important for adding the right amount of sour bite and mineral complexity (magnesium chloride may be useful to reach higher levels without excessive sulfate). Sulfate should be kept relatively low because it doesn't lend positive attributes in sour styles.

In a Gose, the water profile adds a "refreshing" minerality. At least 200 ppm sodium and 400 ppm chloride is suggested. Higher levels of sulfate are also fine, but probably shouldn't exceed 80–100 ppm.

See Adjusting brewing water.

Fruit, herbs, and other adjuncts
First, a note about adjunct flavors: The souring methods described above allow easy production of complex beers packed full of flavor, often with lots of fruit character. They do NOT need fruit or any other adjuncts to be amazing!

The reason so many US commercial sour beers contain fruit or other flavoring is that those breweries use the antiquated kettle souring method, which leaves a beer very bland by boiling away the bacteria flavor and all but completely muting the yeast flavor.

That said, sour beer is a great base for a fruit beer since most fruits are naturally sour. Fruit should be added toward the tail end of fermentation. This helps retain the maximum amount of volatile fruit flavors by limiting the amount of CO₂ that is liberated while the fruit is present.

Recipe: Really Easy Fruit Sour

See also: Soured Fruit Beer on Milk the Funk

Lactose - It is fine to add lactose to sour beers produced with these methods, except for the Fast & Funky method. Lactobacillus will not consume all of of the lactose depending on the amount you add. However certain strains of Brett can fully metabolize lactose (and it's not broken down by glucoamylase).

Gruit is flavored with interesting herbs and reportedly pairs well with souring.

Oak can add great dimension to a beer, and the tannins can add body as well. Oak chips, oak tea, or oak flavoring are likely the best options considering the short timeline in which these beers are produced.

Modern blending program

Coming soon.

Science

(In progress)

Why does sour taste increase with increased alkalinity?
As long as there is sugar, Lacto will continuously produce lactic acid until the pH drops to inhibitory levels (or if hops are introduced).

The alkalinity (carbonate or bicarbonate) reacts with the initial lactic acid produced. Hydrogen ions are be consumed and lactate ion is left behind (and no sour taste).

Once the alkalinity is consumed, then lactic acid will be able to establish its equilibrium:

Lactic acid ⇌ hydrogen ion + lactate ion

Even though the increased lactate ion (produced through neutralization) doesn't add sourness directly, it does so indirectly. Le Chatelier's Principle explains what happens when you add lactate into the equilibrium: the amount of lactic acid increases, and the amount of hydrogen ion decreases. The decrease in hydrogen ions (increased pH) allows the LAB to produce even more lactic acid.

If the goal is to increase sour taste, definitely adjust mash pH using some form of lactic acid (if needed): mineral lactic acid, acidulated malt, or sauergut.

This phenomenon likely explains why titratable acidity (TA) is a better measure of sour taste than pH.

More about sour taste:
Each acid has a particular set of taste characteristics, which include the time of perceived onset of sourness, the intensity of sourness, and any lingering of aftertaste. Sourness is evoked largely by the hydronium ion (H⁺ + H₂O ⇌ H₃O⁺) of acids, and also the character of the anion to a lesser extent. However, the proton concentration (i.e., pH) of a solution is not the main determining factor for sour taste. For example, at a given pH, organic acids such as lactic acid taste more sour than do mineral acids such as HCl. This is because protonated (neutral charge) organic acid molecules readily traverse the cell membrane of taste cells, dissociate and acidify the cytosol, and thereby excite the cell. In other words, as the small amount of hydronium ions is neutralized in the mouth, more undissociated acid (HA) molecules ionize to replace the hydronium ions lost from equilibrium. As a general rule, weak acids have a stronger sour taste than strong acids at the same pH because they exist primarily in the undissociated state.

Still, as pH decreases, the acid becomes more undissociated and imparts more of a sour taste. For example, the intense sour notes of lactic acid at pH 3.5 may be explained by the fact that 70% of the acid is undissociated at this pH, compared with 30% for citric acid.

Some sources hypothesize that protons (and not undissociated acids) enter the taste cells and so depolarize the cell via sodium channels. However this raises an issue of sensory coding that has not yet been addressed, namely, how the animal can discriminate between sour and salty tastes if protons and sodium—both monovalent cations—activate the same receptors by means of the same mechanism. The implication is that other transduction processes for acids remain to be discovered.

It is unclear how taste cells transduce a sour taste because acids (specifically protons) have diverse effects on cell membranes. It has been shown that acids in a single receptor cell may block ion channels, permeate ion channels, change intracellular pH, and alter transporter function. Although the variety of effects and potential targets are well recognized, until recently there has been little success in characterizing the molecular species involved in the transduction machinery.

• https://www.ajevonline.org/content/16/1/29 Acids and the Acid Taste. I. The Effect of pH and Titratable Acidity
• https://beerandbrewing.com/understanding-ph-and-titratable-acidity-in-sour-beer-tools-for-brewers-and/
• https://naldc.nal.usda.gov/download/16133/PDF
• https://www.thebeveragepeople.com/how-to/beer/articles/adjusting-sour-beer-acidity.html
• http://www.milkthefunk.com/wiki/Titratable_Acidity
• https://www.facebook.com/groups/MilkTheFunk/permalink/1415038255191051/?hc_location=ufi
• https://onlinelibrary.wiley.com/doi/full/10.1002/jib.447?fbclid=IwAR2B4xAs4dawfIkq0tiQH5oYAqoMyvz3PZgEIxp2xa-Nv7nbt69mo9-nhp4 Impact of buffering capacity on the acidification of wort by brewing‐relevant lactic acid bacteria

What's with all the italics?
Microbial genera and species are supposed to to italicized in formal writing. See the CDC's guidelines for more info.

See also

• Milk the Funk is a great resource and explains modern methods of mixed fermentation.
• The thread on homebrewtalk.com discussing modern fast souring with Lactobacillus.
• Check out Milk the Funk "The Podcast", especially the "Kettle Sour" and the "Lactobacillus" podcasts: http://www.milkthefunk.live or on Itunes or your favorite podcast service. ???