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 had 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 -- it can sour along with the yeast fermentation rather than reqiring 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.

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. A lot of that extra complexity comes from isovaleric acid production, which 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.

Basic 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. Anyone who knows how to brew beer can follow these steps. Yeast and bacteria are pitched at the same time, hence the name.

1. Make unhopped wort. Boiling is optional.
2. Chill, transfer to fermenter, and aerate as normal.
3. Pitch Lactobacillus plantarum and pitch the yeast.
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 is pitched after the yeast.

1. Make unhopped wort. Boiling is optional.
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. 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

Fast and 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. I'm a nutshell, this method is a post-sour, with highly fermentable wort pitched with both Sacc and Brett from a starter. All parts of the process 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. Optional/recommended: Choose a grain bill that is 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%).
2. Optional/recommended: For maximum fermentability, mash around 145-150°F (62-65°C) for 2 hours. If step mashing, use a couple of long beta rests.
3. Optional: Boil 30-60 minutes.
4. Do not add any hops!
5. Chill as normal.
6. Optional/recommended: Drain some of the wort into a sanitized container to make a starter for the Lactobacillus. (See Lacto starter)
7. Pitch Saccharomyces yeast.
8. Pitch Brettanomyces yeast. You need to make a Brett starter beforehand. (See below)
9. Add glucoamylase enzyme (AKA amyloglucosidase).
10. Ferment as normal, at 65°F (18°C) or higher.
11. 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).
12. Optional/recommended: Add hops when it reaches the desired sourness. (Dry hops or hop tea)
13. Package as normal.

Additional techniques and tips

As with any aspect of brewing, there are many skills and processes to help improve your beer, make it unique, and adjust it to your own taste.

Lactobacillus starter

1. The starter volume should be roughly 1-2% of the batch volume, so about 200-400mL for a 5 US gallon (20L) batch.
2. Add 20g/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 warm, 68-98°F (20-37°C). Swirl it occasionally if you can -- try to mix in the calcium carbonate.

Brettanomyces starter

Making a starter for Brettanomyces is similar to making a starter for Saccharomyces, except it needs to ferment longer, about a week or more, and stirring is not needed.

Increasing or decreasing 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.

Adding Brett at bottling

The "Fast and 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.

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)

• https://www.brunwater.com/articles/add-depth-to-your-sours

Recipes

Hops:
Anecdotally, anywhere from 0.5 oz to 1 oz per 5 gallons adds a nice hop character and completely inhibits further souring.

Almost none of the traditional styles have fruit: Berliner, Gose, Saison, Kvass, Lambic, Gueuze, Flanders Red, Oud Bruin, Lictenhainer, Faro... Only fruit lambics traditionally have fruit, and they aren't traditionally dessert sweet like Lindemanns pasteurized series. These commercial fruit smoothies and sours with all kinds of unusual flavor adjuncts (like cucumber sushi curry) are unique American creations, often improperly labeled with the traditional style names.

The RenewLife bacteria blend adds a lot of flavor and there are many very flavorful fruity yeast strains (including Brett) that can be used with the post-sour method. For example, WLP644 + WY5526 + Lacto makes a sour pineapple + mango + cherry beer with that indescribable Brett character and it's amazing. It also develops a very nice horseblanket if you allow it to age.

WLP644 post-soured makes a great beer without the Brett, and doesn't need temperature control so it's very newbie-friendly! There are plenty of other fruity flavorful yeasts as well.

Hoppy sours can be quite good. Amarillo is popular for good reason. Czech Saaz works really well too.

Also, malt can obviously add plenty of flavor. Flanders Red is one example. The Munich, crystal, and small amounts of Special B malt and oak really complement the cherry Brett character and mix of lactic sourness and slight acetic tang. Grab a bottle of Duchesse de Bourgogne or Rodenbach Grand Cru and give either of those a try. Plenty of other malts are good for adding dimension too, beyond what I've mentioned.

In a gose, the water profile adds a refreshing minerality. Coriander is traditional, or hops can be used for flavoring in non-traditional spin on this style.

Gruit is flavored with interesting herbs and probably does well with souring.

These souring methods I've presented allow easy production of complex beers that don't need fruit or any other adjuncts... Not one-note kettle sours. Of course, if you do like fruit beer, it's probably best to make sour beer as the base since most fruits are naturally sour so it better complements the fruit character.

Modern blending program

Coming soon.

Science

Why does sour taste increase when calcium carbonate is added to a bacterial growth medium?

It comes down to the fact that this is an equilibrium:

Lactic acid ⇌ hydrogen ion + lactate ion

It's helpful to think of the reaction with calcium carbonate as a separate process, and it is because it's not an equilibrium. Until the calcium carbonate is consumed, all the lactic acid and hydrogen ions will be consumed, leaving behind lactate (and no sour taste).

Once the calcium carbonate is consumed, then lactic acid will be able to establish its equilibrium. Even though lactate ion doesn't add sourness directly, it does so indirectly. Le Chatelier's principle explains what happens with the increased amount of lactate ion: when you add lactate into the equilibrium, the amount of lactic acid increases, and the amount of hydrogen ion decreases. This effect of increased lactic acid is amplified in our scenario because the decrease in hydrogen ions allows the LAB to produce even more lactic acid.

This same effect occurs with higher amounts of alkalinity in your brewing water, although I'd presume only if you don't neutralize it with something other than mineral lactic acid, acidulated malt, or sauergut.

https://www.sciencedirect.com/topics/nursing-and-health-professions/sour-taste

One study concluded that TA values were more indicative of perceived sourness by the sensory panel, as compared to pH values.

Flavor Modification Sourness or tartness is one of the five major taste sensations: sour, salty, sweet, bitter, and umami (the most recently determined). Unlike the sensations of sweetness and bitterness, which can be developed by a variety of molecular structures, sourness is evoked only by the hydronium ion of acidic compounds.

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. Some acids impart a stronger sour note than others at the same pH. 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. 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 (eqn (1)). The newly released hydronium ions are then neutralized until no acid remains. Taste characteristics of the acid are an important factor in the development of flavor systems.

1 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.

Sour taste is a function of the acidity of a solution, depending primarily on the proton concentration and to a lesser extent on the particular anion involved.

The perception of sour taste is influenced not only by the activity of the proton, but also by the quality and character of the anion. The role of anion has not been studied in detail at receptor level.

The proton concentration (i.e., pH) of a solution is not the main determining factor for sour taste.2 For example, at a given pH, organic acids such as acetic and citric acids taste more sour than do mineral acids such as HCl. This is because protonated (and therefore having net neutral charge) organic acid molecules readily traverse the cell membrane of taste cells, dissociate and acidify the cytosol, and thereby excite the cell.

In mammals, it is hypothesized that protons enter and so depolarize the cell via sodium channels. 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

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. ???