Alternative Bacteria Sources

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Sources for Lactic Acid Bacteria, especially Lactobacillus, are available in various forms such as unpasteurized products and probiotics. This page contains a list of sources that Milk The Funk members have experimented with, and their results. Note that the production of products such as probiotics may not be as sanitary as brewing industry yeast manufacturers, so without isolating these bacteria on agar plates, they cannot be considered pure cultures. Methods contained on this page use only materials that a typical homebrewer would have on hand and are geared towards brewers without agar plating capabilities. For information on isolating pure cultures of Lactobacillus with selective media on agar plates, see the Lactobacillus and wild yeast isolation pages. For more information on using Lactobacillus to sour wort or kettle sour, see Wort Souring. For more information on mixed fermentation, see Mixed Fermentation.

Yogurt Souring

 
Mike Karnowski from Green Man Brewery Blueberry Berliner Weisse made from a yogurt starter
Yogurt Souring refers to the method of souring wort using unpasteurized yogurt. Greek yogurt is often made with Lactobacillus acidophilus [1]. Using cultures of L. acidophilus from yogurt reportedly can make a 3.0-3.5 pH sour wort in 24 hours, without producing vomit/fecal flavors and aromas. To sour 5 gallons of wort with yogurt, make a 1 liter batch of unhopped starter wort the day before brew day. Add 2-4 teaspoons of live yogurt to the starter wort. Maintain a 100-110°F (37.8-43.3°C) temperature for about 24 hours. On brew day, and after the 24 hour sour starter is finished, mash and sparge a low IBU wort as normal, boil for a few minutes, and then chill the wort down to 100-110°F (37.8-43.3°C). Pitch the yogurt starter into the wort, and hold the temperature as close to the 100-110°F (37.8-43.3°C) range as possible. Bubbling CO2 through the wort is advised if possible to prevent potential off flavors, but is not required. Within 24 hours, the wort should be down in the 3.x pH range. Boil the wort, adding any hops that the recipe calls for, yeast nutrient, etc., and then cool the wort down to Saccharomyces pitching temperatures. Bob's your uncle! [2]

Many strains of L. acidophilus, which is one of the more common species of Lactobacillus found in yogurt, produce toxins that can kill other species of Lactobacillus. See Lactobacillus bacteriocins for more information.

Brands of Yogurt

In general, non-fat Greek yogurt that is unpasteurized works best. Brands of yogurt that have been reported to be successful with this method:

Culturing Lactobacillus From Grains

 
Derek Springer's grain starter
If the brewer wants to use the LAB found naturally on the husks of grains, and doesn't want to risk pitching grains into the entire batch of wort, a Lacto starter with grain can be made. The benefit of this is that if the culture contains any vomit, fecal, or putrid aromas, it can be thrown away and tried again. If the starter needs to be dumped, try again with a different malt source; microbial populations can vary greatly between maltsters, harvest years, and malt type [7]. The following is Derek Springer's grain starter process on the Five Blades Brewing blog [8]:
  1. In a 2L flask make a standard starter wort (1.040 OG).
  2. Add 1/2 tsp 88% lactic acid (should get pH down to 4.0 - 4.5 to help inhibit off-flavor producing microbes).
  3. Add 2 cups uncrushed malt (using acidulated malt is not required).
  4. Top off with carbonated water.
  5. Cap with an airlock.
  6. Keep as warm as you can for 2-3 days, ~110°F is best.
  7. After 2-3 days, strain the grains out using a colander. If no off aromas are detected, pitch the entire starter into the wort using one of the methods described on the Wort Souring page.

If the starter is not going to be used right away, storing it in the fridge for up to a couple of weeks should be fine. If the starter still smells sweet/vegital then it should be ok to use. However if the starter starts to produce aromas of feces or vomit, do not use it [9].

Safety note: do not drink wort from grain starters. It has been reported that wort soured from grain often carries live Salmonella bongori for at least two days after souring, which is associated with non-lethal food poisoning. This microbe will die during or after primary fermentation See Malt Inoculated Wort and Wild Yeast Starters and Safety for more information.

For science, see also:

Culturing from Kefir

Commercial kefir will have the microbial populations listed on the bottle. Many include Lactobacillus spp. The above process should also work well for home fermented kefir. Pietro Caira from MTF offers this guidance on culturing from commercial kefir products (President's Choice and Liberté brands specifically tested): [10]

  1. Let the kefir warm to room temperature.
  2. Shake the kefir up in the bottle, and add to an unhopped 1 liter starter of ~1.040 SG DME wort (for a 5 gallon batch of beer).
  3. Incubate at a temperature of ~100°F for 24 hours (room temperature may work too).
  4. This results in a starter pH of about 3.2.
  5. Add the entire starter to wort using one of the methods described on the Wort Souring page.

Culturing from Sauerkraut

 
Pellicle from Alex Loijos's sauerkraut culturing experiment.

Culturing LAB from sauerkraut can be done in much the same way as kefir. This study shows that culturing Lactobacillus from sauerkraut is most likely best done when the sauerkraut is at least 7-14 days old, however after 60 days more acid resistant Lactobacillus cells can be cultured. The following instructions can be used to culture LAB from sauerkraut (and probably from other fermented vegetables) for a 5 gallon batch: [11]

  1. Use 100 mL of at least 14 day old brine, but preferably 60 day old brine, and allow it to warm to room temperature if cold.
  2. Add the brine to a 1 liter starter of ~1.040 DME wort (alternatively use Samuel Aeschlimann's Lactobacillus starter recipe).
  3. Incubate with an airlock at a temperature around ~90°F.
  4. Wait until the starter clears. This may take several days. When it clears, the starter is done. It may show signs of yeast fermentation.
  5. After fermentation finishes, add the entire starter to the wort. Reference the Wort Souring page for further brewing procedures.

Alex Loijos described an interesting process on MTF of culturing successive microbes from a starting batch of sauerkraut. After preparing his sauerkraut, each day he took a sample of the developing brine and pitched it into the same batch of wort. This most likely had the effect of pitching Leuconostoc and Weissella species during days 1-3, and then Lactobacillus species starting on day 7.

The results of this experiment were interesting: "I just tried it cold. It's definitely drinkable!! It tastes like sourdough bread with the tart/salty/bready malt combination. I didn't perceive the viscosity as much and I think it's in part because it's flat that it feels 'thick.' I'm pretty pleased with the surprises along the way during this experiment. Chiefly that there were wild yeast that were capable of 71% attenuation, which I didn't expect! I was just using the kraut brine for souring, and expected I would have to pitch a culture after. Is there anything else like this that provides a pretty much guaranteed full spectrum of wild microbes (yeast and LAB)? Not yogurt, not grain, not coolships in the open air..." ~ Alex Loijos.

Culturing from Probiotics

Some commercial probiotics have been successfully used to produce Lactobacillus cultures (many brands have also failed at providing usable bacteria according to some homebrewers [12]). Probiotics that are classified as "dietary supplements", as opposed to "drugs", may not be as free of contaminates as pure cultures from brewing industry yeast labs [13]. The following probiotics are examples of brands, methods, and results that MTF members have had [14]. Dried forms of Lactobacillus should be stored refrigerated because viability has been seen to decrease as much as 80x when stored at room temperatures [15]. Use only fresh products whenever possible (viability of Lactobacillus drops quickly over time in general), avoid products that have been stored at room temperature (pill and liquid format), and don't bother using expired products [16]. Making a starter is a good way to ensure that the cells are still viable.

See this Sui Generis Blog article on which Probiotics to avoid based on the genera of microbes they contain. Probiotics should have their contents listed plainly on their packaging. Avoid probiotics for animals as they tend to contain organisms that produce off-flavors such as Enterococcus, Clostridium, or Bacillus [17]. If souring wort, also avoid any probiotics that have Saccharomyces species in them because lactic acid bacteria can have a tough time quickly producing acidity if it is competeing with an active yeast fermentation.

"Reverse MTF Method"

Moved to Mixed Fermentation; Souring Without Brettanomyces.

General Tips and Experiences on Using Probiotics

  • The use of even small amounts of hops with probiotics, especially L. plantarum based probiotics, will greatly inhibit their souring effect. It is recommended not to use any hops while the probiotics are souring wort or beer (hops can be added post-souring; adding hops post-souring, even dry hopping, will usually stop the lactic acid production).
  • Tips/experiences of breaking up pills first or letting them dissolve, using starters vs no starter, and number of pills to pitch.
  • For GoodBelly shots, only 1-2 shots (or 8 oz from a 32 oz carton) for 5 gallons of wort are needed (~20 billion cells for 5 gallons). That scales to a 1.5 - 2 cartons per BBL for the commercial scale (although some have reported that just over 1 carton per BBL is enough; freshness plays a factor) [18]. If using fresh GoodBelly that has been stored cold, don't bother making a starter (by checking to see if the pH gets lower, a starter will tell you if the bacteria is viable, but it will also increase the possibility of contamination). Mango is the preferred flavor because it imparts little flavor to the beer, but others can be used as well [19].
  • Starters can be avoided for fresh tablet probiotics that have been stored cold, although measuring the pH of a starter will verify that the probiotic pills are still good to use. For Swansons L. plantarum tablets (5 billion cells per tablet), 7-10 tablets for 5 gallons of wort and held at 80-100°F for 1-2 days reportedly works well (temperature control and very warm temperatures are not necessary for L. plantarum in general) [20].
  • Both liquid and pill format probiotics are extremely shelf unstable. They should be stored cold. Liquid probiotics may not be viable after two weeks of cold storage (see expiration date on the package). If liquid or pill format probiotics are stored at room temperature or warmer for any length of time, they may not be viable and a starter is recommended to see if they will acidify wort [21]. Note that cultures from brewing labs have reportedly better shelf lives than probiotics [22].
  • According to a representative of GoodBelly™ on MTF: "You're guaranteed 20 billion (cells) at time of consumption (often more)... We know that our products are within the claimed probiotic count range during shelf-life but every product has different count stability characteristics. The dynamics of the change/decline in cell counts is very different at room temperature than it is at refrigeration temperature... Fizziness may come from high metabolic activity or growth of Lp299v. A fizzy product may or may not have elevated counts as – at some point – the counts may go down again when high levels of lactic acid are in the product...StraightShot and our SuperShots are the most (cell count) stable. " [23]
MTF Member Source Process Results
Matt Firetto Swanson Plantarum Probiotic Pills Starter:

4 capsules Swanson Plantarum probiotic in 1 liter of 1.040 wort fermented in high 70°'s F in garage. After 36hr PH ~3.6 (using cheap wine PH strips) Tasted clean and noticeably sour with fairly strong yogurt like aroma. (not how I would want my beer to smell)

Starter chilled overnight and decanted most liquid before pitching

Single infusion mash all grains at 153°F for 1hr 4.5 gallons strike water 3 gallons sparge water After mashing and sparging, wort heated to 190°F for 10 minutes and cooled to 95°F for souring used 12% acid malt in my mash to help drop the PH before adding the Lacto. Wort PH 4.5 using colorfast strips Wort gravity 1.040 pre boil/pre lacto Pitched decanted lacto starter Flushed Kettle with CO2, covered in plastic wrap and lid

Wort PH ~3.7 gravity 1.038 pre boil/after 24 hrs (using cheap wine PH strips) No off aromas, nice fresh grain aroma. Tastes very clean, sweet, not as acidic as starter. 60 minute boil - 1 oz tettnang at 10 minutes .5oz tangerine peel and nutrient at 5 mins. Post boil gravity 1.040 Pitched US05 at 70°F Fermented for 10 days and kegged at final gravity 1.013

Tasted after 10 days in keg.

Pours with bright white head, which mostly recedes but leaves good lacing. Simple aroma of grain and lactic sour aroma. No off or funky aromas. Taste is very bright with a sharp and simple sourness. No bitterness or hop flavors, but I think the tangerine peel helped to add more complexity to the sour flavors. Light grain character with just a little bit of sweetness.

I also drank this side by side with an Ithaca Cruiser Berliner Weiss. Overall the beers were very similar. The Ithaca beer had a stronger grain aroma and a little less lactic sourdough aroma. Both beers seemed to have about the same perceived level of acidity. The acidity in my beer was just a little brighter than the Ithaca beer, but overall the two were very similar.

David Frank GoodBelly Probiotic Drink Warmed up 2 GoodBelly probiotic drinks to room temperature and then pitched it into unboiled wort (in a purged keg). Sour worted at 95°F. Starting pH was around 4.7 (pre-acidified the mash).

ph at 3.73 after 15 hours

pH at 3.68 after 24 hours

pH at 3.65 after 36 hours

pH at 3.5 after 48 hours - massive co2 (and possibly ethanol) production...when I purged the keg, the beer exploded out. The keg was under around 30psi. Very messy to get it out of the keg and into the kettle.

Beer was then boiled for 20min, chilled and fermented with Kölsch yeast.

Brett Smith GoodBelly Flavored Drinks Probiotic Drink 700ml starter of 1.040 wort. Chill to 95°F. Fill to 1000 with GoodBelly drink. I like the mango as it doesn't seem to leave much aroma at all. Let this starter go for 24 hours. You'll see the massive growth.

Brew beer however you choose. Cool to 100°F. Pitch GoodBelly starter. Let temperature free fall. Check pH in 24 hours, should be 3.4-3.6. I like to let my culture go 36 hours and I'm almost guaranteed 3.4. Then pitch yeast to ferment.

Described this above.
Ed Coffey Swanson's L. plantarum Probiotic Pills Cracked open 3 pills and added to 750ml of DME starter wort, kept at 90°F for 36 hours then pitched into 100°F wort. I've done this twice now, reached a PH of ~3.30 in 48 hours at 95-100°F.
Abel GoodBelly Probiotic Drink Let warm up to temp and pitch straight in. Ph before 5.4, ph at the end was 3.2. Temp held at 95°F for 3.5 days then pitch Sacch and lowered to regular ferment temp.
Viktor Nyman ProViva Superfrukt Probiotic Drink Made a starter of 200 ml juice and 800 ml OG 1040 wort. Fermented at 35°C for a few days, cooled to refrigerator temperature and decanted into a sanitized container. A few days before the brew day, I made a new starter from the decanted bacteria and 500 ml of OG 1040 wort. Fermented at 35°C. Pitched the whole starter into a 15 litre batch. The starter had a starting pH of 4.5 and was under 3 pH in 24 hours. This was when fermenting at 35°C.

The beer itself started at 4.8 pH and I boiled it when it reached 3.2-3.3 somewhere 21 hours later.

Result is clean and lactic without any sign of spoilage bacteria related off flavours (throw up, cheese, butyric acid etc.).

Drew Wham GoodBelly Products (L. plantarum) Their products contain 20 billion cells of the 229v L. planetarium strain per serving. In a 5 gal batch a single serving will reduce the pH to 3.2 in 48-72 hours held at 95°F. Good results in over 12 batches.
Dan Graston Swanson Probiotics 1 capsule in 1 quart of canned starter wort (1.039, 4.44pH, not DME) at 90°F. Starter pH barely dropped for first 24 hours because the Lacto powder just sank to the bottom and never went into suspension, which was unexpected. After rousing, the pH dropped to 3.23 over the next 36 hours. No drop in gravity. Test starter, so no beer was produced.
Allen Stone LactoGG 2 capsules were used in 1 liter of 1.030 wort, and held in high 90°F's for 72 hours before stepping up to 5 liters and pitched after another 7 days. The powder from the capsules fell to the bottom of the starter initially and needed rousing before it started fermenting. I only had test strips, which indicated a ph in the high 3s. I tasted the wort at this point and it had produced some co2, but not much, and a slight tartness. I added Custersianus to ferment out and there has sat for many months. I sampled it recently and it is not great. Slightly tart, but not enough to stand on its own. I would like to do this again with more control, and build a small starter that is pitched into a larger volume of wort, then held at a higher temp. I suspect that because of the makeup of Lacto GG and its ability to survive internal body temp, it may need to work In the low 100s to really go to work. I would say it is a viable option, but not enough info is known at this time to give any suggestions.
Stuart Grant [24] Ethical Nutrients - IBS Support (Australia) Added 120 billion cells. Pitched at 29°C/84°F, and I'm letting it fall to room temp. 20 hours since pitching got to 3.87 pH. Temp has dropped to 20°C/68°F. No change in SG (1.045). After 25 hours, temp down to 19°C and pH down to 3.67. After 35 hours, temp 18°C, pH 3.53, SG 1.045 (unchanged). Lactic flavour is very clean; slightly apple like. It barely tastes tart with all that sugar. After 44 hours, temp 18°C, pH 3.43, SG 1.045 (unchanged). I split the wort in half. First half I boiled for 20 mins with some hops then pitched US-05; second half I did not boil, but added dry hops and Lochristi Brett slurry. The no-boil version which had Lochristi Brett added is down to 1.016 and pH 3.32, while the boiled version pitched with US-05 is down to 1.008 and pH 3.23 (weird that it's lower). Brett version is quite funky with some acetic acid. Clean version is super clean, and ready for bottling soon. Lovely clean sourness. The dry hops come across as lemon zesty. Superbly refreshing! See Stuart's blog post.
Marius Loktu [25] ProbiMage melkesyrebakterier (available in Norway, Sweden, and Denmark) I tend to use 6-8 per 20-25L. (just the content) Turning off heat at about 35C, rack to carboy and pitch content of capsules. Let it naturally reach ambient. Then I pitch yeast after 2-3 days. (always gets me below 3.5 PH) Always sticking with 0 IBU. Have started playing around with co-pitching and pitching lacto after the yeast as well. To get more yeast character from primary. Its capsules. So you just open them up and use the powder inside. It's good not having wet hands doing this. Good results reported.
Hrafnkell Freyr Magnússon [26] Bio-Kult Made two kettle soured beers with this probiotic and they both came out great. The second I pitched 11x capsules in ~22 liters of wort and it dropped to pH 3.2 in just under two days at 32°C. Taste is nice and clean. Will definitely use this strain more.

Health Benefit Claims

Using Sourdough Starter

Using Ginger Bug

Matt Spaanem on MTF on using ginger bug: "A ginger bug is just wild yeast and bacteria harvested from ginger root. Just grate up some ginger and add it to some sugar water. After a few days it starts visibly fermenting and you've got your bug... FG 0.995 makes this ~4.3% (OG ~1.028) uncarbed it's a bit dry/puckering/tannic (probably from the tea) with a friendly orangey/coriander flavored tartness and some funk hiding in the background. Ginger follows you throughout and lingers on the tongue. Overall it's good, if a bit dry. I may chaptalize the keg if it still annoys me after its carbed. I should give these bugs a go in an all malt 'real' beer... it was pretty good carbed and dry. I've since used the bug to ferment an actual beer (with malt/grain derived sugars instead of just sucrose) and it was very attenuative and the Brettanomyces made itself known for sure, the Lactobacillus less so, the beer was hopped to 8 IBU. It was in primary for 5 months and has been in secondary for ~2 months to see if anything more happens with it.

As for using ginger bug, I just treat it like any other yeast culture. Once you harvest it from the shredded ginger mixed with sugar water pitch it into a larger batch, use some nutrient. I haven't done any isolating or looking at it under the microscope, but based on behaviors and flavors produced, I believe my bug contains Saccharomyces, Brettanomyces and Lactobacillus (though maybe not Lactobacillus anymore after passing through hopped wort). Obviously you're not guaranteed to catch all of these, it depends on your piece of ginger used, but you're probably likely to catch some yeast and Lactobacillus.

According to Sandor Katz, ginger is also a wild source for Aspergillus oryzae, the mold used to break down rice starches in sake and other rice wines. I tried harvesting it once, it worked, but I couldn't keep my incubation chamber quite warm enough so I also got another mold (probably Aspergillus niger) that produces citric acid and the resulting fermented millet and rice beverage tasted almost exactly like lemon juice... I'll probably try this again now that I have a proper fermentation chamber that I can turn up to 95-100F that should (hopefully) inhibit the citric acid forming mold." [29]

Kombucha SCOBY

The microbiome of kombucha SCOBYs varies from culture to culture. They can include various yeasts, including Saccharomyces, Saccharomycodes, Schizosaccharomyces, Zygosaccharomyces, Brettanomyces/Dekkera, Candida, Torulospora, Kloeckera, Pichia, Mycotorula, and Mycoderma. They also commonly contain some sort of acetic acid bacteria such as Gluconobacter, Gluconacetobacter, or Acetobacter species, which form the "leather pancake"-like SCOBY of kombucha. Some kombuchas (30%) have also been found to have species of Lactobacillus [30].

Reports so far seem to indicate that fermenting with limited exposure to oxygen produces better results. Since SCOBY's contain Acetobacter, fermenting with exposure to too much oxygen produces a very vinegar tasting beverage. Another approach is to ferment with exposure to air until the beer tastes as acidic as intended and then use an airlock to stop the aerobic fermentation; this will allow the Acetobacter to be more active and have a greater effect on the flavor of the beer since it needs oxygen in order to ferment [31]. Another method for controlling the amount of acetic acid is blending finished kombucha with finished beer.

Peppers

Natural Wines

It might be possible to culture microbes from "natural" or spontaneously fermented wines. Some producers may still use some amount of sulfites, however. Try to find a young wine, hopefully unfiltered and low sulfites or unsulfited. These wines may also contain wild yeasts, including Brettanomyces. Methods for attempting to use these microbes are described on Commercial Sour Beer Dregs Inoculation.

See also:

See Also

References

  1. ↑ Lactobacillus acidophilus Wikipedia page. Retrieved 3/3/2015.
  2. ↑ Conversation with Mike Karnowski of Green Man Brewery on the MTF Facebook group. 3/3/2015.
  3. ↑ 3.0 3.1 Mark Fry on the MTF Facebook group. 2/19/2015.
  4. ↑ Brewing with Yogurt. The Not So Professional Beer Blog. Retrieved 3/3/2015.
  5. ↑ Conversation with Mike Karnowski on MTF about Seven Stars Yogurt. 6/17/2015.
  6. ↑ Conversation about using Sigi's Skyr Yogurt on MTF. 08/10/2016.
  7. ↑ Microbial Populations on Barley
  8. ↑ Conversation with Derek Springer on Milk The Funk. 4/4/2015.
  9. ↑ Conversation with Bryan of Sui Generis Blog on MTF. 11/18/2016.
  10. ↑ Conversation with Peitro Caira on MTF regarding Kefir. 10/22/2015.
  11. ↑ Conversation with Ingo Janssen on MTF. 12/23/2015.
  12. ↑ Conversation on Reddit. April 2015.
  13. ↑ Regulatory Oversight and Safety of Probiotic Use. Veena Venugopalan, Kimberly A. Shriner, and Annie Wong-Beringer. Nov 2010.
  14. ↑ Conversation on MTF about using Probiotics. 5/22/2015.
  15. ↑ Conversation with Bryan of Sui Generis Blog on Milk The Funk. 05/04/2015.
  16. ↑ GoodBelly FAQ. Retrieved 07/23/2016.
  17. ↑ Conversation with DeWayne Schaaf on MTF. 12/17/2015.
  18. ↑ Various MTF Members. Milk The Funk thread on how many cartons of GoodBelly to use. 09/14/2017.
  19. ↑ Conversation on MTF about how many GoodBelly shots to use for kettle souring. 08/29/2016.
  20. ↑ MTF thread on how many Swansons tablets can be pitched directly without a starter. 01/20/2016.
  21. ↑ Conversation with Devin Bell about storage and viability of probiotics. 10/25/2016.
  22. ↑ Conversation with Malcolm Frazer on MTF regarding shelf life of OYL Lacto. 11/03/2016.
  23. ↑ Marla and Armin from GoodBelly™. Milk The Funk Facebook group. 07/05/2017.
  24. ↑ Stuart Grant's experience with Aussie probiotics. 10/15/2015.
  25. ↑ Conversation with Marius Loktu about Norwegian probiotics on MTF. 04/18/2016.
  26. ↑ Hrafnkell Freyr Magnússon. Milk The Funk Facebook group post about Bio-Kult probiotic. 01/30/2018.
  27. ↑ Francesca Rita Dinardo, Fabio Minervini, Maria De Angelis, Marco Gobbetti, Michael G. Gänzle. Dynamics of Enterobacteriaceae and lactobacilli in model sourdoughs are driven by pH and concentrations of sucrose and ferulic acid. LWT, Volume 114, 2019. 108394, ISSN 0023-6438. https://doi.org/10.1016/j.lwt.2019.108394.
  28. ↑ "Raw Flour and Dough". CDC website for Food Safety. Retrieved 09/23/2024.
  29. ↑ Conversation with Matt Spaanem on MTF regarding using ginger bug in beer. 05/09/2015.
  30. ↑ A Review on Kombucha Tea—Microbiology, Composition, Fermentation, Beneficial Effects, Toxicity, and Tea Fungus. Rasu Jayabalan, Radomir V. Malbasa, Eva S. Loncar, Jasmina S. Vitas, Muthuswamy Sathishkumar. 2014.
  31. ↑ Private correspondence with Ron Davis by Dan Pixley. 07/06/2017.
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