Sour beer

Renew Life Ultimate Flora co-sour with passion fruit and vanilla, courtesy of Dgallo on HomeBrewTalk

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.

The Bacteria

Lactobacillus plantarum is the 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 - on Amazon and in grocery and drug stores like Walmart
• Lallemand WildBrew Sour Pitch - from The Beverage People and Amazon, 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 will work, but they 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.

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.

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

Co-sours, courtesy of Dgallo on HomeBrewTalk

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 (ideally from a starter).
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.

Pitching bacteria without a starter has given inconsistent results, so we currently recommend making a starter for the Lacto before brew day to ensure the culture is healthy enough to sour the beer quickly.

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	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 Souring phase adds time Fermentation is slower	Normal
Recommended Yeast Pitch Rate	Normal	Normal	Higher pitch rate recommended	Normal
Recommended Bacteria Pitch Rate	Low-moderate	High	Very high	N/A
Able to control hop rate?
Able to control sourness?
Avoids high contamination risk?
Allows yeast flavor expression?			(minimal)	(Limited selection)
Probiotic bacteria survive?
Desirable bacteria flavor?			(minimal)
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 Saccharomyces and Brettanomyces 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 to the fermenter.
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. 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 beers 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

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.

1. Add 100 g/L dry malt extract to a container such as an Erlenmeyer flask, a canning jar, or a small pot.
2. Optional/recommended: Add 20 g/L calcium carbonate.
3. Optional/recommended: Add 2 g/L quality yeast nutrient.
4. Top off to the desired volume with chlorine-free water.
5. Stir and heat the mixture to a boil.
6. Remove from heat, cover, and allow to cool. An ice bath may be used to speed up the cooling.
7. If a pot used for heating, transfer the wort to a sanitized jar or flask.
8. Add Lactobacillus plantarum to the starter wort. Only a small amount is needed (e.g. the contents of one probiotic capsule).
9. Cover (with foil or stopper+airlock) and let it sit somewhere between 68–98°F (20–37°C).
10. Swirl it occasionally. Try to mix in the calcium carbonate when stirring. It should be ready to use in about 24 hours. It should be hazy and have a aroma different from wort.

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. You will know the Lacto is alive if the starter is cloudy and has an aroma sort of like yogurt or iced tea (not just normal wort aroma in any case).

Brettanomyces starter

Making a starter for Brettanomyces is similar to making a starter for Saccharomyces, except it often needs a longer time to grow. 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 2-3 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 3-7 days.
   • If possible, control temperature to about 77°F (25°C).
   • Ideally you should stop stirring it when it's finished growing since you don't want a lot of acetic acid production.

If you don't have a stir plate, just swirl it often. Additional time will likely be needed (a week or more).

If propagating a small culture using multiple "steps" (a series of starters), consider limiting the number and size of steps because of possible THP formation.

The starter generally shouldn't be cold crashed, but it should be stored cold if it won't be used within a couple weeks.

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

Co-sour with Hibiscus and Passion Fruit Purée, courtesy of Dustin_J on HomebrewTalk

Decreasing sourness is pretty straightforward:

• Pitch less Lacto.
• Ferment cool, closer to 65°F (18°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.
• Consider adding acetic acid, which can increase the perceived sharpness of the sour taste. (See below)
• Increased levels of magnesium and sulfate may be helpful to increase perceived sourness, as would lower levels of sodium.
• Increase the carbonate/bicarbonate in your brewing water (yes, higher alkalinity). It might be beneficial to add calcium carbonate (or possibly calcium lactate, potassium carbonate or sodium bicarbonate) directly to the fermenter; this is somewhat untested but results have been promising. (See the Science section below)
• A more "natural" way to increase the buffering capacity and therefore sourness is to perform a step mash starting low (45-52 °C), and adjusting pH to around 5.3. This step increases both the dissolved proteins and phosphates, both of which acts as buffer systems in wort/beer.

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 at the time of packaging, using any vinegar product 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 add 0.3–0.6 g/L acetic acid to the beer, a good range for a nuance of complexity. A bench trial is also a good option to determine the right amount for your taste. A lower amount may be needed if the product is very flavorful, such as balsamic vinegar. 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.

Using the right process, there's no risk of "turning the whole batch to vinegar", even when using vinegar with a live acetic acid bacteria culture. Acetic acid production is an aerobic process, and therefore limiting oxygen exposure prevents additional acetic acid formation.

Recipes

Pretty much any sour beer recipe found elsewhere can be adapted to use modern methods. Just follow a modern process with whatever malt, yeast, and hops the recipe lists. Just be sure to use L. plantarum as the bacterium. The one exception is that blended yeast/bacteria cultures (that contain Pedio and low Brett cell counts) may not give good results in a short timeframe.

Ingredient suggestions

Yeast

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

Fruity Saccharomyces
WLP644 Sacch Trois A20 Citrus OYL200 Tropical IPA A04 Barbarian OYL052 DIPA	Tropical, pineapple, mango, peach, apricot, orange
OYL-061 Voss Kveik OYL501 Gulo	Fresh orange and orange marmalade +/- peach
WY1318 London Ale III GY054 Vermont IPA A38 Juice	Fruity, English esters
WLP1983 Charlie's Fist Bump	Lightly fruity, berries and apple
Fruity and phenolic Saccharomyces
WLP300 Hefeweizen WY3068 Weihenstephan Weizen WY3638 Bavarian Wheat	Banana, fruit, and clove, vanilla
WLP500 Monastery WLP530 Abbey Ale WY3522 Belgian Ardennes WY1214 Belgian Abbey BE-134 Lallemand Abbaye B56 Rustic WY3726 OYL500 Saisonstein's Monster	Fruity (plum, cherry, pear, banana), bubblegum, spice
WLP565 Belgian Saison I SafAle T-58 WY3711 French Saison Belle Saison	Earthy, peppery, spicy, citrusy
Brettanomyces
WY5526 Brett Lambicus	Cherry pie
WY5112 Brett Bruxellensis	Sweaty horse blanket
TYB207	Tart tropical fruit, SweeTarts™
TYB Amalgamation II	Balanced funk, SweeTarts™, lemon, pineapple, guava, mango, papaya

Bacteria

Raspberry milkshake was co-sour with Omega 605 Lacto blend, courtesy of Dgallo on HomeBrewTalk

It is currently unknown how different bacterial cultures compare in terms of flavor. However, it stands to reason that a blend of species such as Renew Life Ultimate Flora would add more flavor complexity than a single strain.

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. If Brett is present, it often metabolizes anything that might be undesirable (such as isovaleric acid).

The majority of souring occurs within a couple days, but 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.

Malt

Wheat (malted or unmalted) is a very common component of sour beer because it is used in a lot of traditional styles. It may help add body.

A good simple malt bill to let the microbes (and/or adjuncts) shine would be around 70% pale base malt and 30% white wheat malt, or if brewing with extract, use 50% wheat DME and 50% pale DME.

There are also a lot of options for making malt-forward sours, or using malt to add interesting dimensions to a beer. Flanders Red and Oud Bruin are good examples of malty traditional sour styles. To emulate either of those, you could use a recipe for a red ale or brown ale respectively. Sour stouts and porters are also enjoyed by some, although roasted character should be kept relatively low since it may clash with sourness. Smoked malt can also be interesting, as in a Lichtenhainer (smoky pale sour). Another idea is to include some dark Belgian candi syrup to make something like 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:

Hop	Flavors
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
Galaxy	Citrus, peach, passion fruit
Medusa	Guava, melon, apricot, and citrus
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 necessarily kill the Lacto, they tend to only stop growth and metabolism, particular in lower amounts.

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)
• 5–30 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 Water.

Fruit, herbs, and other adjuncts

Post-sour with WLP644 and blueberry, courtesy of Jag75 on HomeBrewTalk

First, a note about adjunct flavors: The reason so many US commercial sour beers contain fruit or other flavoring is that those breweries use the antiquated kettle souring method. Kettle souring results in a very one-note bland beer because the bacteria flavor is boiled away, the yeast flavor is muted by pre-souring, and the sourness tends to overpower subtle malt character (combined with high-oxygen hot side practices).

The modern souring methods described here allow easy production of complex beers packed full of flavor, often with lots of fruit character from the microbes and/or hops. They do NOT need fruit or any other adjuncts to be amazing beers!

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).

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

Oak
Natural oak products 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.

Candy
Candy had been used successfully as a flavor adjunct (and it also presumably increases the alcohol content). See this thread on HomeBrewTalk.

Science

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

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 some other intervention like added hops).

Any alkalinity (carbonate or bicarbonate) that is present reacts with the initial lactic acid produced. The reaction consumes the hydrogen ions on the lactic acid, leaving behind lactate ions with no sour taste.

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

Lactic acid ⇌ hydrogen ion + lactate ion

Even though the additional lactate ion (produced by the reaction with a base) doesn't add sourness directly, it does so indirectly. Le Chatelier's Principle explains what happens when you add lactate into the equilibrium: lactic acid increases, and hydrogen ion decreases. The decrease in hydrogen ions (increased pH) allows the Lacto to produce even more lactic acid. The larger amount of lactic acid causes more sour flavor.

If your goal is to increase sourness, then you should adjust mash pH using some form of lactic acid (if needed): lactic acid solution, acidulated malt, or sauergut. Because all of these contain lactic acid, they will leave behind lactate when neutralizing alkalinity.

More about sour taste:

Blackberry and peach post-sours using GoodBelly, courtesy of fendersrule on HomeBrewTalk

The variable alkalinity of brewing water, and the variability of buffering capacity between different beers likely explains why titratable acidity (TA) is a better measure of sour taste than pH.

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.

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. For example, at a given pH, lactic acid tastes more sour than mineral acids such as HCl because there is more undissociated acid. The particular acid, the TA, and pH all definitely play a role in sour taste. As pH decreases, the acid becomes more undissociated and imparts more of a sour taste, even if it's just because there's a reserve of protons that would ionized at the higher pH in the mouth. 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.

There is some disagreement among scientists regarding the mechanics of exactly how an acid causes a sour taste — whether it's evoked largely by the hydronium ion (H⁺ + H₂O ⇌ H₃O⁺) concentration (i.e., pH) or whether it's due to undissociated acid directly entering the taste cells before ionization.

One hypothesis is that protonated (neutral charge) organic acid molecules traverse the cell membrane of taste cells, dissociate and acidify the cytosol, and thereby excite the cell. Another hypothesis is that protons (and not undissociated acids) enter the taste cells and so depolarize the cell via sodium channels.

Either way, all of the acid will give up its protons in the mouth due to the buffering effect of saliva; 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. However this raises an issue of sensory coding that has not yet been addressed, namely, how we can discriminate between sour and salty tastes if protons and sodium — both monovalent cations — activate the same receptors by means of the same mechanism. It is also unclear how taste cells transduce a sour taste because 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. The implication is that other transduction processes for acids remain to be discovered.

See also

• The thread on homebrewtalk.com discussing modern fast souring with Lactobacillus.
• Milk the Funk is a great resource and explains modern methods of mixed fermentation.

Potential resources:

• "Antibacterial and Antifungal Activities of Spices."
• https://embracethefunk.com/
• http://suigenerisbrewing.com/
• http://suigenerisbrewing.com/index.php/2020/11/22/probiotic-beer/
• https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-58-0094
• Aneta Ciosek, Katarzyna Fulara, Olga Hrabia, Paweł Satora, Aleksander Poreda, Chemical Composition of Sour Beer Resulting from Supplementation the Fermentation Medium with Magnesium and Zinc Ions, Biomolecules, 10.3390/biom10121599, 10, 12, (1599), (2020).