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'''Wort Souring''' is a process in which ''[[Lactobacillus]]'' is given a "head start", pitched before the yeast so that it will be able to produce significant amounts of lactic acid before the ''Saccharomyces'' completes the main fermentation. There are several variations on souring wort, including souring in the primary fermenter, souring in a secondary vessel, or even souring in the boil kettle itself. There are also various methods of inoculating the wort with ''Lactobacillus''. Finally, the brewer has the option of pasteurizing the wort by heating it to kill the ''Lactobacillus'' before adding the yeast for the main fermentation. Some creative brewers have applied wort souring techniques to longer aged [[Mixed Fermentation]] beers and barrel aged beers. Many brewers prefer this process over [[Sour Mashing]] because it can be easier to control, and when implemented properly it produces a clean sour beer in a short amount of time. The possibility of pasteurizing the soured wort also makes this a good method for making sour beers with a lot of residual malt sweetness (e.g. sour barley wines), and should also make it attractive to brewers who are concerned about infection issues in their cold side equipment (equipment that is used post-boil) <ref>[http://sourbeerblog.com/fast-souring-lactobacillus/ Miller, Matt. Dec 20, 2014. "Fast Souring with ''Lactobacillus'' – Best Practices, Sensory, & Science". Sour Beer Blog.]</ref>. When sour worting, some brewers first [[Sour_Worting#How_to_Pre-Acidify|lower the pH of the wort to 4.0-4.3]] before pitching ''Lactobacillus''. This has sometimes been found to help the head retention of the beer, and helps to protect the wort from contaminating microorganisms. For more information, see the [[Lactobacillus#Foam_Degradation|''Lactobacillus'' page section on Foam Degradation]].
Generally, ''[[Pediococcus]]'' is not used with this method (''Pediococcus'' is generally used in long aged [[Mixed Fermentation]] sours with ''[[Brettanomyces]]''), however [[Pediococcus#Commercial_Pediococcus_Cultures|Bootleg Biology]] has released a blend of ''Pediococcus'' strains that are reportedly good for sour worting.
Important note regarding aluminum pots: souring in an aluminum vessel may strip the aluminum of the protective oxide layer. The oxide layer is only stable at a pH of 4.5 - 8.5. Therefore, kettle souring in an aluminum pot is generally not recommended <ref>[http://www.pfonline.com/articles/aluminum-surface-finishing-corrosion-causes-and-troubleshooting Aluminum Surface Finishing Corrosion Causes and Troubleshooting. W. John Fullen, Boeing Research and Technology & Jennifer Deheck, Boeing, Seattle, Washington, USA. 10/17/2014.]</ref>.
<blockquote>"''Mixed culture fermentation for sour beers produces one thing, and (kettle souring) produces another thing. If you’re going to make a malty red ale that is kettle soured, don’t call it a Flanders Red. Honor the tradition.''" - Sean Burke of the Commons Brewery, Kettle Souring Presentation, CBC 2015.</blockquote>
==Processes==
===Souring in the Boil Kettle===
Also known as '''kettle souring''', souring in the boil kettle is a simple process that is often used if the brewer wants to subsequently heat pasteurize the wort. Pasteurizing the wort has the advantage of allowing the brewer to rack the pasteurized wort into a fermenter and pitch brewer's yeast without fear of an ongoing ''Lactobacillus'' infection in their post-boil equipment.
The brewing process is the same for any all grain batch up until the first wort and sparge runnings are collected into the boil kettle. The temperatures that a typical mash out/sparge reach should be enough to pasteurize the wort <ref name="pasteurization">[http://science.howstuffworks.com/life/cellular-microscopic/pasteurization4.htm Heat pasteurization]</ref>, however we advise heating the wort for a short (1-2 minutes) boil in order to kill a greater degree (2-3 logs more) of thermotolerant microbes <ref name="Heit_boiling">[https://www.facebook.com/groups/MilkTheFunk/permalink/1180630378631841/?comment_id=1180634488631430&reply_comment_id=1180677581960454&comment_tracking=%7B%22tn%22%3A%22R2%22%7D Conversation with Bryan of Sui Generis Blog regarding boiling versus lower temperature pasteurization. 11/18/2015.]</ref><ref>[http://sourbeerblog.com/lactobacillus-2-0-advanced-techniques-for-fast-souring-beer/ ''Lactobacillus'' 2.0 – Advanced Techniques for Fast Souring Beer. 11/18/2015. Retrieved 11/19/2015.]</ref>. Once all of the wort is collected in the boil kettle (and preferably brought to a boil), the wort is chilled to around 80-115°F (37-46°C), depending on the ''[[Lactobacillus]]'' culture that is being used. Once chilled to the temperature that is appropriate, the wort in the kettle is inoculated with a culture of ''Lactobacillus''. Hops should not be added at any point before inoculating the wort with a culture of ''Lactobacillus''; most species of ''Lactobacillus'' will be inhibited by the presence of even very small amounts hops (1-2 IBU or even just hop material from dry hopping). When using a pure culture of ''Lactobacillus'', it is generally a good idea to [[Lactobacillus#Starters_and_Pitching_Rate|create a 500 mL starter]] for ~5-6 gallons of wort.
There are various ways of inoculating the wort. A reliable method is pitching a pure culture of ''Lactobacillus'', or a blend of ''Lactobacillus'' cultures. Alternatively, a handful of unmilled malted barley can be added to the kettle for inoculation instead of a pure culture, since the husks of grain carry many microorganisms. If unmilled grain is added, it is thought that filling the head space of the kettle with CO2 will help decrease off-flavors such as "footiness" from [[Isovaleric Acid]], which are produced by aerobic microbes that are naturally present on the grain <ref name="khris_johnson">Personal correspondence with Khristopher Johnson of Green Bench Brewing Co. and Dan Pixley. 05/24/2016.</ref>. Keeping the temperature between 109-115°F (42.8-46°C) will encourage the ''Lactobacillus'' resident on the grain and will discourage other bacteria. Temperature consistency is critical during this process <ref name="young_grains">[https://www.facebook.com/groups/MilkTheFunk/permalink/1356058381089039/?comment_id=1356464531048424&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Jeff Young from Blue Owl Brewing Co on souring from grains. 07/21/2016.]</ref>. Lowering the pH of the [[Sour_Worting#How_to_Pre-Acidify|wort to under 4.5 (ideally 4.0 - 4.3)]] will also discourage many other bacteria from thriving in the wort during the incubation period. This will also help with head retention <ref>[[Lactobacillus#Foam_Degradation]]</ref>. Souring with grains should occur within 1 or 2 days if done correctly <ref name="young_grains"></ref>. Consider [[Alternative Bacteria Sources]] for more reliable approaches to using "wild" ''Lactobacillus'', or ''Lactobacillus'' from sources other than yeast labs.
If a pure culture of ''Lactobacillus'' bacteria is used it is ideal but not necessary to fill the head space of the fermenter with CO2 gas (some brewers have reported that this will help reduce sulfur in the finished beer). Keeping positive pressure in the kettle with CO2 will help prevent contaminates that create [[Butyric Acid|butyric acid]] and other off-flavors from entering the kettle due to negative pressure, and is often the approach that commercial brewers take <ref>Personal correspondence with Steph Cope of CraftHaus Brewing Co. 02/06/2016.</ref>. The kettle should be held at the desired temperature for 24-72 hours (in some cases longer, but no longer than 5 days). Depending on the strain of ''Lactobacillus'', and the desired sour level, the time of incubation is ultimately a variable that is up to the brewer (see the ''[[Lactobacillus]]'' page for suggested temperatures and times for specific strains). The kettle lid should be firmly in place and optionally sealed with plastic wrap so that other microorganisms do not get in. Potential for formation of [[Butyric Acid]] and [[Isovaleric Acid]] when using only a pure culture is extremely slight to none assuming contamination does not occur.
Once the level of acidity is reached (this can be tested with a reliable [[PH_Meter|pH meter]], or in the case of using a pure culture can safely be taste tested), the wort is brought to a boil. The wort may be boiled normally in the case of any style of beer that requires a longer boiling process, or it it may be boiled for no more than a minute or two in the case of making a [[Berliner Weissbier]]. Technically speaking, the wort doesn't need to be boiled at all (this is called [http://www.garshol.priv.no/blog/331.html Raw Ale]). Heat pasteurization at 170°F (76.6°C) for 15 minutes should kill the ''Lactobacillus'' culture being used to sour the wort <ref name="pasteurization" />.
Deciding whether or not to boil the wort can also depend on whether or not there was a considerable amount of alcohol produced, which commonly happens when the wort is contaminated with yeast. Pure cultures of ''Lactobacillus'' do not show typical signs of fermentation that we are used to seeing with yeast fermentations, such as forming a krausen, producing a lot of CO2, or fermenting wort more than ~1.005 gravity points (see [[100% Lactobacillus Fermentation]]). If a yeast contamination produces a significant amount of alcohol during the souring process, then this presents a problem when it comes to boiling. Although 100% pure ethanol boils at 173.1°F/78.4°C <ref name="boiling_of_alcohol">[http://chemistry.about.com/od/moleculecompoundfacts/f/What-Is-The-Boiling-Point-Of-Alcohol.htm Boiling temperature of ethanol]</ref>, the lower the concentration of ethanol in the wort (technically beer at this point), the higher the temperature required for boiling off the ethanol. For example, at 5% ABV it takes approximately 197°F/92°C for the ethanol to boil <ref>[http://www.clawhammersupply.com/blogs/moonshine-still-blog/12243869-making-moonshine-still-temperature Making Moonshine: Still Temperature. Retrieved 01/11/2016.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1212116758816536/?comment_id=1212140998814112&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Russell Carpenter on MTF. 01/11/2016.]</ref>. Time is also required to boil off the ethanol, so this may not be as big of a concern as it first appears (''warning: vaporized ethanol is highly flammable)''. Another and perhaps more important consideration is that, unlike unfermented wort, boiling and high heat pasteurization temperatures can have a negative effect on the flavor of fermented beer. Beer already has anti-bacterial properties, such as low pH, presence of alcohol, and hops (although hops may not be present in wort being soured), so higher pasteurization temperatures aren't necessarily required for beer. For these reasons, the beer industry commonly heat pasteurizes beer at 140°F/60°C for 15 minutes, and this is also adequate for pasteurizing soured beer <ref>[http://www.sciencedirect.com/science/article/pii/S0023643806002854#bib16 A suitable model of microbial survival curves for beer pasteurization. Sencer Buzrul. 2006.]</ref>. In the case of an accidental yeast contamination during the souring process, another option is to simply dump the batch and start again with a pure culture of ''Lactobacillus''.
Once the soured wort is boiled or heat pasteurized, it can be safely added to the primary fermenting vessel without worries of future infections. The wort is aerated as normal, and brewer's yeast, or ''[[Brettanomyces]]'' yeast is then pitched into the wort as normal (usually brewer's yeast is used if infection of cold side equipment is a concern). At a pH of 3.4 or lower, the acidity of the wort can reportedly effect the fermentation of some strains of brewer's yeast <ref name="low ph">[http://www.homebrewtalk.com/f127/no-hop-berliner-weisse-415067/index3.html#post5280971 Michael Tonsmeire on HBT]</ref>. It is recommended to pitch a healthy starter of yeast, possibly with a higher cell count than normal. In the case of using dry yeast, re-hydrating as per the manufacturer's recommendations and using a yeast nutrient like Go-Ferm is recommended. Many yeast strains have been successfully used by MTF members to ferment pre-acidified wort: US05, S04, WY1098/WLP007/OYL-006, Belle Saison, Sacch Trois, Bret brux, B. clausenii, B. custersianus, Bret Drie (BSI), WY3711, and WY3726 to name a few (see reference) <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1105185972842949/ Conversation on MTF about using specific yeast strains in acidic wort. 7/6/2015.]</ref>. Brewers who are having difficulty fully fermenting pre-acidified wort can try growing their yeast in the soured wort (pasteurize the soured wort first if needed) with yeast nutrients (Fermaid K + DAP, for example). This assumes that the wort still has a lot of sugar left over after souring (if not, DME can be added). See [[Saccharomyces#Fermentation_Under_Low_pH_Conditions|Fermenting in low pH conditions]] for more information.
===Souring in the Primary Fermenter===
Wort can be soured in the primary fermenter before adding other yeasts. This is generally a good approach for brewers who aren't concerned with pasteurization and infections of their cold side equipment. This has the advantage of possibly producing a more complex sour beer overall, or at least a sour beer that will evolve over time. It has the advantage over a more traditional [[Mixed Fermentation]] in that ''Lactobacillus'' is used to guarantee at least a certain level of sourness. This is also a good process to use for making a [[Berliner Weissbier]].
The process is very similar to the sour worting technique, except the wort is never pasteurized after it is soured. The all grain brewing process is the same for any all grain brewing process, except that after the boil the beer is only chilled to the recommended temperature for the ''Lactobacillus'' strain that the brewer is going to use. Using grain husks for souring with this method is not advised since the grain will stay in the fermenter during primary fermentation, and unwanted microbes on the grain husks would potentially have a longer exposure to the wort. Instead, the brewer should use a pure strain of ''[[Lactobacillus]]''. As a result of not using grains to sour the wort, there is less concern of developing [[Butyric Acid]] or [[Isovaleric Acid]] with this method. Even still, lowering the pH of the [[Sour_Worting#How_to_Pre-Acidify|wort to under 4.5 (ideally 4.0 - 4.3)]] will also discourage contaminating bacteria from thriving in the wort during the incubation period. This will also help with head retention <ref>[[Lactobacillus#Foam_Degradation]]</ref>. There is also the option of [[Mixed_Fermentation#Reusing_a_Sour_Yeast_Cake|using a sour yeast cake]] from another sour beer as the bacteria inoculation.
Once cooled to the desired temperature (usually around 90-115°F or 32.2-46°C), the wort is racked to the primary fermenting vessel. Note that the wort should contain a low amount of IBU's when using this process since IBU's can inhibit many (but not all) species of ''[[Lactobacillus]]''. Using no hops is a good approach to getting more acidity, but if hops are required then using less than 6 IBU's is a good guideline in general (consider mash hopping; mash hopping has been reported to reduce IBU's by ~70% <ref>[http://www.homebrewersassociation.org/how-to-brew/resources/conference-seminars/ ''Putting Some Numbers on First Wort and Mash Hop Additions''. David Curtis NHC 2014 Presentation.]</ref>). It is generally a good idea to create a 500 mL starter before hand for ~5-6 gallons of wort (see [[Lactobacillus#Starters_and_Pitching_Rate|''Lactobacillus'' starters]]). Once the wort is racked to the primary fermenting vessel, the ''Lactobacillus'' culture is added directly to the fermenter. No other yeasts are added at this time. The ''Lactobacillus'' bacteria is allowed to incubate by itself in the wort for 2-5 days with the before mentioned target temperature maintained throughout the incubation period (some ''Lactobacillus'' species/strains may continue to produce acidity under lower temperatures). The exact time frame of incubation depends on the species/strain of ''Lactobacillus'', the manufacturer's recommendation, and the brewer's desired acidity level. Acidity can safely be measured with a reliable pH Meter throughout this time. If possible, it is advised that the brewer fill the head space of the fermenter with CO2. Some brewers have reported that this helps to reduce sulfur production, but if ''Brettanomyces'' is added to the beer later on in the process and allowed to age, this shouldn't be a concern.
After the desired acidity level is reached from the incubating ''Lactobacillus'' bacteria, the brewer can crash cool the fermenter down to the temperature that is desired for the primary fermenting yeast. Both ''[[Saccharomyces]]'' and ''[[Brettanomyces]]'', or a blend can be used as primary fermenting yeast. ''Brettanomyces'' is often chosen because of it's higher tolerance of a low pH environment (3.4- pH <ref name="low ph">[http://www.homebrewtalk.com/f127/no-hop-berliner-weisse-415067/index3.html#post5280971 Michael Tonsmeire on HBT]</ref>), although many ''Saccharomyces'' strains have been successfully used (see the [[Sour_Worting#Souring_in_the_Boil_Kettle|Souring in the Boil Kettle]] section above). If the chosen yeast requires aeration and the brewer has the ability, the sour wort should be aerated before pitching yeast. Brewers have had good luck using Fermentis dry yeast products in non-aerated wort. Re-hydrating the dry yeast as per the manufacturer's instructions and with a yeast nutrient such as Go-Ferm is effective <ref>[http://www.scottlab.com/product-102.aspx Go-Ferm]</ref>. The wort is then fermented out as normal. The brewer can consider other [[Brewing Methods]] such as pitching ''Brettanomyces'', a mixed culture, or commercial sour beer dregs into secondary.
===Souring in Another Vessel Before Racking to the Primary Fermenter===
This process is very similar to sour worting in the kettle. This method is ideal for those who wish to use grains to introduce ''Lactobacillus'' to the beer. If done properly, the formation of [[Butyric Acid]] and [[Isovaleric Acid]] should be minimal.
The wort is mashed and sparged as normal (and alternatively brought to a short boil), and is then lowered to somewhere between 109-115°F (42.8-46°C). This temperature favors ''Lactobacillus'', while discouraging Enterobacteriaceae. Optionally, the mash pH can be lowered to 4.4 with lactic acid or acidulated malt to further discourage Enterobacteriaceae activity. Once the desired temperature (and optionally pH) is reached, a handful of fresh malted unmilled grain is added to the mash and allowed a few minutes to inoculate the mash with the microbes found naturally on the grain husks. The wort is then transferred to a second vessel such as a glass carboy. The vessel should be filled to the very top, minimizing the oxygen levels inside the vessel. The vessel should be stored in a heated environment that maintains a temperature between 109-115°F (42.8-46°C) for 1 to 3 days depending on how much acidity the brewer wants (the faster the souring process the better; Jeff Young from Blue Owl achieves the desired acidity in about 18 hours usually) <ref name="young_grains"></ref><ref name="james_spencer">[http://beerandwinejournal.com/sour-wort-berliner/ Spencer, James. December 15, 2014. Beer and Wine Journal.] </ref>.
Once the 1 to 4 day time period has been reached, the wort is transferred to the boil kettle and boiled as normal. Boiling will kill all of the microorganisms in the wort, and will provide the option for adding hops and other kettle additions. Just as with kettle souring, the wort doesn't have to be boiled, but can be instead heat pasteurized at 170°F (76.6°C) for 15 minutes <ref name="pasteurization" />, or at 140°F (60°C) for 15 minutes if a yeast contamination produced a significant amount of alcohol. Once boiled or pasteurized, the wort can be chilled and handled in the same way as the above methods for wort souring.
[http://beerandwinejournal.com/sour-wort-berliner/ James Spencer provides an article] that fully explains his process, as well as a step by step video guide and tasting on Beer and Wine Journal <ref name="james_spencer" />.
===Tips on Maintaining Heat for Homebrewers===
Keeping the temperature as steady as possible for a pure culture ''Lactobacillus'' fermentation is not that important. Just try to stay in the range of the temperature best suited for a given species (see the [[Lactobacillus#Culture_Charts|''Lactobacillus'' culture charts]]). Here are some tips from MTF members on maintaining warm temperatures for sour worting <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1279628395398705/ Tips from many MTF members on maintaining heat for sour worting. 04/07/2016.]</ref>:
:''Editor's note: please be cautious when using heat sources to heat plastic fermenters; PET bottles have been known to melt or warp when applying too much heat to them.''
* For metal vessels such as a kettle, keep it on the stove burner and turn the burner on when heat is lost.
* Put the wort in a plastic bucket and seal with lead, then lower that bucket into a ten gallon water cooler and close the lid. Optionally, insulate with blankets.
* Use a glass carboy FermWrap™ heater attached to a sensor thermowell through the cap and a temperature controller.
* Use a Brew Belt Fermentation Heating Belt and wrap a "hoody" sweater or some other fabric around it to insulate, and a temperature controller.
* Use an aquarium heater (Enheim band recommended), fill a large plastic cooler with water and keep the water warm with the aquarium heater. Set the souring vessel in the cooler.
* Use an [http://anovaculinary.com/ Anova sous vide device] - place the vessel in a larger vessel with water, and keep the heat applied to the outside water with the Anova. Works well for maintaining heat for starters too.
* If not using a plastic vessel, keep the vessel in an oven (if it fits) or an electric smoker.
* Use a [http://www.amazon.com/Zoo-Med-Reptile-Cable-14-75-Feet/dp/B001OVBEEK/ref=sr_1_1?ie=UTF8&qid=1460052384&sr=8-1&keywords=zoomed+reptile+heat+cable ZooMed Reptile Heater Cable] inside of a fermentation chamber. Line the inside of the chamber walls with the wire and secure with duct tape.
* If maintaining heat is not possible with any of the techniques mentioned, use a species such as ''L. plantarum'' that produces acidity at room temperature. [[Lactobacillus#Omega_Yeast_Labs_on_OYL-605|Omega Yeast Labs OYL-605]] works well without hot temperatures.
===How to Pre-Acidify===
After the production of the wort, but before pitching the culture of ''Lactobacillus'', some brewers like to slightly lower the pH of the wort with food grade lactic acid (available at homebrew stores) or phosphoric acid before adding the ''Lactobacillus''. Acidifying the wort before pitching ''Lactobacillus'' has several benefits, such as discouraging unwanted microbes that may have accidentally been introduced into the wort, and helping to prevent [[Lactobacillus#Foam_Degradation|''Lactobacillus'' from degrading foam proteins]]. The idea is to get the wort down to a pH of 4.0 - 4.4 before adding ''Lactobacillus''.
There currently is no formula for how much lactic acid to add to a volume of wort due to the different buffering capacities of wort <ref>[http://www.mbaa.com/districts/Northwest/Events/Documents/Study%20in%20the%20Practical%20Use%20of%20Lactic%20Acid%20Bacteria.pdf A Study in the Practical Use of Lactic Acid Bacteria. Greg Doss from Wyeast Laboratories Inc. 2014.]</ref>. Water chemistry spreadsheets and formulas geared towards mash pH adjustments may not be accurate for wort pH adjustments since wort does not contain grain material, however there has been reports on MTF and recommendations from Martin Brungard (author of Bru'n Water) that [https://sites.google.com/site/brunwater/ Bru'n Water] can accurately determine how much lactic acid is needed to lower a wort's pH, or at least provide a starting point <ref name="delange_brungard"></ref>. We encourage readers to experiment with water chemistry calculators to see if they can accurate predict wort pH adjustments or get a starting point for how much acid to add <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1244954842199394/?comment_id=1245053585522853&comment_tracking=%7B%22tn%22%3A%22R%22%7D MTF Thread with Landon Ortiz. 03/03/2016.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1290987234262821/?comment_id=1353870694641141&reply_comment_id=1354548117906732&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Conversation with Adam Boura and Mark Trent on MTF regarding using Bru'n Water for adjusting wort pH. 07/18/2016.]</ref>.
Another method of finding out how much acid to add would be to pull a measured portion of the wort out, and add acid in measured amounts until the desired pH is reached. The amount of acid added can then be scaled up to the full volume of the wort. A.J. Delange suggests that the buffering capacity of wort might be half that of the mash (based on the kilograms of malt used in the mash) <ref name="delange_brungard">[http://www.homebrewtalk.com/showthread.php?t=587124 A.J. Delange. Homebrewtalk Thread. 07/19/2016.]</ref>.
Trial and error might be the most practical approach for homebrewers that don't have an abundance of wort to spare for finding out how much acid to add to a sample and scaling that up. Post boil, the wort pH is generally around 5.0 - 5.2. Adjusting the pH of wort before pitching ''Lactobacillus'' can then be done fairly easily by taking a trial and error approach. Using 1 mL of 88% lactic acid per .1 shift in pH for 5 gallons of wort is a good starting measurement. As an example, say that 5 gallons of wort has a pH of 5.0 just before pitching the ''Lactobacillus'' culture. Begin by adding 5 mL (1 US teaspoon) of food grade lactic acid to the wort for a target of ~4.4 pH. Stir gently, then take another pH reading. Continue to add 1-2 mL of lactic acid until the wort has the desired pH. Derek Springer has observed that it takes about one tablespoon (15 mL) of 88% lactic acid to reach a pH of 4.2 - 4.5 for 5 gallons of wort <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1290987234262821/?comment_id=1291031577591720&comment_tracking=%7B%22tn%22%3A%22R3%22%7D Conversation with Derek Springer on MTF regarding acidifying wort. 04/24/2016.]</ref>, however a higher amount may be required if the brewer's water is high in bicarbonate (24 mL for 5 gallons of wort to reach a pH of 4.4 was reported by Sean McVeigh for his water which contains 375ppm of bicarbonates <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1290987234262821/?comment_id=1291031577591720&reply_comment_id=1291118190916392&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Sean McVeigh on MTF on acidifying wort. 04/23/2016.]</ref>). Once a pH of 4.0 - 4.4 is reached, pitch the ''Lactobacillus'' culture. This small amount of lactic acid shouldn't have much of an impact on flavor. If a more precise method for determining the required amount of lactic acid is required, a sample of the wort can be pulled and lactic acid or phosphoric acid can be added to it until the target pH is reached, and then that amount can be scaled up (a micropipette might be required to measure very small amounts of lactic/phosphoric acid).
===Concerns about Dimethyl Sulphide (DMS)===
* See [[Dimethyl Sulfide]].
==See Also==
===Additional Articles on MTF Wiki===
* [[Sour Mashing]]
* [[Alternative Bacteria Sources]]
* ''[[Lactobacillus]]''
* [[Mixed Fermentation]]
===External Resources===
* [http://suigenerisbrewing.blogspot.com/2015/07/how-i-sour-mash-recipe.html "How I Sour Mash & A Recipe"; Sui Generis Blog (includes Sour Worting and microbiology information).]
* [http://www.fivebladesbrewing.com/year-sour-mash/ "Year of the Sour Mash" by Derek Springer. This series of articles were written for his NHC 2015 presentation.]
* [http://sourbeerblog.com/lactobacillus-2-0-advanced-techniques-for-fast-souring-beer/ "Lactobacillus 2.0 - Advanced Techniques for Fast Souring Beer", by Matt Miller of Sour Beer Blog.]
* [https://byo.com/stories/issue/item/3353-overnight-acidification "Overnight Acidification" by Michael Tonesmiere, article for Brew Your Own Magazine on Jan/Feb 2016.]
==References==
<references/>
[[Category:Techniques]]
Generally, ''[[Pediococcus]]'' is not used with this method (''Pediococcus'' is generally used in long aged [[Mixed Fermentation]] sours with ''[[Brettanomyces]]''), however [[Pediococcus#Commercial_Pediococcus_Cultures|Bootleg Biology]] has released a blend of ''Pediococcus'' strains that are reportedly good for sour worting.
Important note regarding aluminum pots: souring in an aluminum vessel may strip the aluminum of the protective oxide layer. The oxide layer is only stable at a pH of 4.5 - 8.5. Therefore, kettle souring in an aluminum pot is generally not recommended <ref>[http://www.pfonline.com/articles/aluminum-surface-finishing-corrosion-causes-and-troubleshooting Aluminum Surface Finishing Corrosion Causes and Troubleshooting. W. John Fullen, Boeing Research and Technology & Jennifer Deheck, Boeing, Seattle, Washington, USA. 10/17/2014.]</ref>.
<blockquote>"''Mixed culture fermentation for sour beers produces one thing, and (kettle souring) produces another thing. If you’re going to make a malty red ale that is kettle soured, don’t call it a Flanders Red. Honor the tradition.''" - Sean Burke of the Commons Brewery, Kettle Souring Presentation, CBC 2015.</blockquote>
==Processes==
===Souring in the Boil Kettle===
Also known as '''kettle souring''', souring in the boil kettle is a simple process that is often used if the brewer wants to subsequently heat pasteurize the wort. Pasteurizing the wort has the advantage of allowing the brewer to rack the pasteurized wort into a fermenter and pitch brewer's yeast without fear of an ongoing ''Lactobacillus'' infection in their post-boil equipment.
The brewing process is the same for any all grain batch up until the first wort and sparge runnings are collected into the boil kettle. The temperatures that a typical mash out/sparge reach should be enough to pasteurize the wort <ref name="pasteurization">[http://science.howstuffworks.com/life/cellular-microscopic/pasteurization4.htm Heat pasteurization]</ref>, however we advise heating the wort for a short (1-2 minutes) boil in order to kill a greater degree (2-3 logs more) of thermotolerant microbes <ref name="Heit_boiling">[https://www.facebook.com/groups/MilkTheFunk/permalink/1180630378631841/?comment_id=1180634488631430&reply_comment_id=1180677581960454&comment_tracking=%7B%22tn%22%3A%22R2%22%7D Conversation with Bryan of Sui Generis Blog regarding boiling versus lower temperature pasteurization. 11/18/2015.]</ref><ref>[http://sourbeerblog.com/lactobacillus-2-0-advanced-techniques-for-fast-souring-beer/ ''Lactobacillus'' 2.0 – Advanced Techniques for Fast Souring Beer. 11/18/2015. Retrieved 11/19/2015.]</ref>. Once all of the wort is collected in the boil kettle (and preferably brought to a boil), the wort is chilled to around 80-115°F (37-46°C), depending on the ''[[Lactobacillus]]'' culture that is being used. Once chilled to the temperature that is appropriate, the wort in the kettle is inoculated with a culture of ''Lactobacillus''. Hops should not be added at any point before inoculating the wort with a culture of ''Lactobacillus''; most species of ''Lactobacillus'' will be inhibited by the presence of even very small amounts hops (1-2 IBU or even just hop material from dry hopping). When using a pure culture of ''Lactobacillus'', it is generally a good idea to [[Lactobacillus#Starters_and_Pitching_Rate|create a 500 mL starter]] for ~5-6 gallons of wort.
There are various ways of inoculating the wort. A reliable method is pitching a pure culture of ''Lactobacillus'', or a blend of ''Lactobacillus'' cultures. Alternatively, a handful of unmilled malted barley can be added to the kettle for inoculation instead of a pure culture, since the husks of grain carry many microorganisms. If unmilled grain is added, it is thought that filling the head space of the kettle with CO2 will help decrease off-flavors such as "footiness" from [[Isovaleric Acid]], which are produced by aerobic microbes that are naturally present on the grain <ref name="khris_johnson">Personal correspondence with Khristopher Johnson of Green Bench Brewing Co. and Dan Pixley. 05/24/2016.</ref>. Keeping the temperature between 109-115°F (42.8-46°C) will encourage the ''Lactobacillus'' resident on the grain and will discourage other bacteria. Temperature consistency is critical during this process <ref name="young_grains">[https://www.facebook.com/groups/MilkTheFunk/permalink/1356058381089039/?comment_id=1356464531048424&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Jeff Young from Blue Owl Brewing Co on souring from grains. 07/21/2016.]</ref>. Lowering the pH of the [[Sour_Worting#How_to_Pre-Acidify|wort to under 4.5 (ideally 4.0 - 4.3)]] will also discourage many other bacteria from thriving in the wort during the incubation period. This will also help with head retention <ref>[[Lactobacillus#Foam_Degradation]]</ref>. Souring with grains should occur within 1 or 2 days if done correctly <ref name="young_grains"></ref>. Consider [[Alternative Bacteria Sources]] for more reliable approaches to using "wild" ''Lactobacillus'', or ''Lactobacillus'' from sources other than yeast labs.
If a pure culture of ''Lactobacillus'' bacteria is used it is ideal but not necessary to fill the head space of the fermenter with CO2 gas (some brewers have reported that this will help reduce sulfur in the finished beer). Keeping positive pressure in the kettle with CO2 will help prevent contaminates that create [[Butyric Acid|butyric acid]] and other off-flavors from entering the kettle due to negative pressure, and is often the approach that commercial brewers take <ref>Personal correspondence with Steph Cope of CraftHaus Brewing Co. 02/06/2016.</ref>. The kettle should be held at the desired temperature for 24-72 hours (in some cases longer, but no longer than 5 days). Depending on the strain of ''Lactobacillus'', and the desired sour level, the time of incubation is ultimately a variable that is up to the brewer (see the ''[[Lactobacillus]]'' page for suggested temperatures and times for specific strains). The kettle lid should be firmly in place and optionally sealed with plastic wrap so that other microorganisms do not get in. Potential for formation of [[Butyric Acid]] and [[Isovaleric Acid]] when using only a pure culture is extremely slight to none assuming contamination does not occur.
Once the level of acidity is reached (this can be tested with a reliable [[PH_Meter|pH meter]], or in the case of using a pure culture can safely be taste tested), the wort is brought to a boil. The wort may be boiled normally in the case of any style of beer that requires a longer boiling process, or it it may be boiled for no more than a minute or two in the case of making a [[Berliner Weissbier]]. Technically speaking, the wort doesn't need to be boiled at all (this is called [http://www.garshol.priv.no/blog/331.html Raw Ale]). Heat pasteurization at 170°F (76.6°C) for 15 minutes should kill the ''Lactobacillus'' culture being used to sour the wort <ref name="pasteurization" />.
Deciding whether or not to boil the wort can also depend on whether or not there was a considerable amount of alcohol produced, which commonly happens when the wort is contaminated with yeast. Pure cultures of ''Lactobacillus'' do not show typical signs of fermentation that we are used to seeing with yeast fermentations, such as forming a krausen, producing a lot of CO2, or fermenting wort more than ~1.005 gravity points (see [[100% Lactobacillus Fermentation]]). If a yeast contamination produces a significant amount of alcohol during the souring process, then this presents a problem when it comes to boiling. Although 100% pure ethanol boils at 173.1°F/78.4°C <ref name="boiling_of_alcohol">[http://chemistry.about.com/od/moleculecompoundfacts/f/What-Is-The-Boiling-Point-Of-Alcohol.htm Boiling temperature of ethanol]</ref>, the lower the concentration of ethanol in the wort (technically beer at this point), the higher the temperature required for boiling off the ethanol. For example, at 5% ABV it takes approximately 197°F/92°C for the ethanol to boil <ref>[http://www.clawhammersupply.com/blogs/moonshine-still-blog/12243869-making-moonshine-still-temperature Making Moonshine: Still Temperature. Retrieved 01/11/2016.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1212116758816536/?comment_id=1212140998814112&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Russell Carpenter on MTF. 01/11/2016.]</ref>. Time is also required to boil off the ethanol, so this may not be as big of a concern as it first appears (''warning: vaporized ethanol is highly flammable)''. Another and perhaps more important consideration is that, unlike unfermented wort, boiling and high heat pasteurization temperatures can have a negative effect on the flavor of fermented beer. Beer already has anti-bacterial properties, such as low pH, presence of alcohol, and hops (although hops may not be present in wort being soured), so higher pasteurization temperatures aren't necessarily required for beer. For these reasons, the beer industry commonly heat pasteurizes beer at 140°F/60°C for 15 minutes, and this is also adequate for pasteurizing soured beer <ref>[http://www.sciencedirect.com/science/article/pii/S0023643806002854#bib16 A suitable model of microbial survival curves for beer pasteurization. Sencer Buzrul. 2006.]</ref>. In the case of an accidental yeast contamination during the souring process, another option is to simply dump the batch and start again with a pure culture of ''Lactobacillus''.
Once the soured wort is boiled or heat pasteurized, it can be safely added to the primary fermenting vessel without worries of future infections. The wort is aerated as normal, and brewer's yeast, or ''[[Brettanomyces]]'' yeast is then pitched into the wort as normal (usually brewer's yeast is used if infection of cold side equipment is a concern). At a pH of 3.4 or lower, the acidity of the wort can reportedly effect the fermentation of some strains of brewer's yeast <ref name="low ph">[http://www.homebrewtalk.com/f127/no-hop-berliner-weisse-415067/index3.html#post5280971 Michael Tonsmeire on HBT]</ref>. It is recommended to pitch a healthy starter of yeast, possibly with a higher cell count than normal. In the case of using dry yeast, re-hydrating as per the manufacturer's recommendations and using a yeast nutrient like Go-Ferm is recommended. Many yeast strains have been successfully used by MTF members to ferment pre-acidified wort: US05, S04, WY1098/WLP007/OYL-006, Belle Saison, Sacch Trois, Bret brux, B. clausenii, B. custersianus, Bret Drie (BSI), WY3711, and WY3726 to name a few (see reference) <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1105185972842949/ Conversation on MTF about using specific yeast strains in acidic wort. 7/6/2015.]</ref>. Brewers who are having difficulty fully fermenting pre-acidified wort can try growing their yeast in the soured wort (pasteurize the soured wort first if needed) with yeast nutrients (Fermaid K + DAP, for example). This assumes that the wort still has a lot of sugar left over after souring (if not, DME can be added). See [[Saccharomyces#Fermentation_Under_Low_pH_Conditions|Fermenting in low pH conditions]] for more information.
===Souring in the Primary Fermenter===
Wort can be soured in the primary fermenter before adding other yeasts. This is generally a good approach for brewers who aren't concerned with pasteurization and infections of their cold side equipment. This has the advantage of possibly producing a more complex sour beer overall, or at least a sour beer that will evolve over time. It has the advantage over a more traditional [[Mixed Fermentation]] in that ''Lactobacillus'' is used to guarantee at least a certain level of sourness. This is also a good process to use for making a [[Berliner Weissbier]].
The process is very similar to the sour worting technique, except the wort is never pasteurized after it is soured. The all grain brewing process is the same for any all grain brewing process, except that after the boil the beer is only chilled to the recommended temperature for the ''Lactobacillus'' strain that the brewer is going to use. Using grain husks for souring with this method is not advised since the grain will stay in the fermenter during primary fermentation, and unwanted microbes on the grain husks would potentially have a longer exposure to the wort. Instead, the brewer should use a pure strain of ''[[Lactobacillus]]''. As a result of not using grains to sour the wort, there is less concern of developing [[Butyric Acid]] or [[Isovaleric Acid]] with this method. Even still, lowering the pH of the [[Sour_Worting#How_to_Pre-Acidify|wort to under 4.5 (ideally 4.0 - 4.3)]] will also discourage contaminating bacteria from thriving in the wort during the incubation period. This will also help with head retention <ref>[[Lactobacillus#Foam_Degradation]]</ref>. There is also the option of [[Mixed_Fermentation#Reusing_a_Sour_Yeast_Cake|using a sour yeast cake]] from another sour beer as the bacteria inoculation.
Once cooled to the desired temperature (usually around 90-115°F or 32.2-46°C), the wort is racked to the primary fermenting vessel. Note that the wort should contain a low amount of IBU's when using this process since IBU's can inhibit many (but not all) species of ''[[Lactobacillus]]''. Using no hops is a good approach to getting more acidity, but if hops are required then using less than 6 IBU's is a good guideline in general (consider mash hopping; mash hopping has been reported to reduce IBU's by ~70% <ref>[http://www.homebrewersassociation.org/how-to-brew/resources/conference-seminars/ ''Putting Some Numbers on First Wort and Mash Hop Additions''. David Curtis NHC 2014 Presentation.]</ref>). It is generally a good idea to create a 500 mL starter before hand for ~5-6 gallons of wort (see [[Lactobacillus#Starters_and_Pitching_Rate|''Lactobacillus'' starters]]). Once the wort is racked to the primary fermenting vessel, the ''Lactobacillus'' culture is added directly to the fermenter. No other yeasts are added at this time. The ''Lactobacillus'' bacteria is allowed to incubate by itself in the wort for 2-5 days with the before mentioned target temperature maintained throughout the incubation period (some ''Lactobacillus'' species/strains may continue to produce acidity under lower temperatures). The exact time frame of incubation depends on the species/strain of ''Lactobacillus'', the manufacturer's recommendation, and the brewer's desired acidity level. Acidity can safely be measured with a reliable pH Meter throughout this time. If possible, it is advised that the brewer fill the head space of the fermenter with CO2. Some brewers have reported that this helps to reduce sulfur production, but if ''Brettanomyces'' is added to the beer later on in the process and allowed to age, this shouldn't be a concern.
After the desired acidity level is reached from the incubating ''Lactobacillus'' bacteria, the brewer can crash cool the fermenter down to the temperature that is desired for the primary fermenting yeast. Both ''[[Saccharomyces]]'' and ''[[Brettanomyces]]'', or a blend can be used as primary fermenting yeast. ''Brettanomyces'' is often chosen because of it's higher tolerance of a low pH environment (3.4- pH <ref name="low ph">[http://www.homebrewtalk.com/f127/no-hop-berliner-weisse-415067/index3.html#post5280971 Michael Tonsmeire on HBT]</ref>), although many ''Saccharomyces'' strains have been successfully used (see the [[Sour_Worting#Souring_in_the_Boil_Kettle|Souring in the Boil Kettle]] section above). If the chosen yeast requires aeration and the brewer has the ability, the sour wort should be aerated before pitching yeast. Brewers have had good luck using Fermentis dry yeast products in non-aerated wort. Re-hydrating the dry yeast as per the manufacturer's instructions and with a yeast nutrient such as Go-Ferm is effective <ref>[http://www.scottlab.com/product-102.aspx Go-Ferm]</ref>. The wort is then fermented out as normal. The brewer can consider other [[Brewing Methods]] such as pitching ''Brettanomyces'', a mixed culture, or commercial sour beer dregs into secondary.
===Souring in Another Vessel Before Racking to the Primary Fermenter===
This process is very similar to sour worting in the kettle. This method is ideal for those who wish to use grains to introduce ''Lactobacillus'' to the beer. If done properly, the formation of [[Butyric Acid]] and [[Isovaleric Acid]] should be minimal.
The wort is mashed and sparged as normal (and alternatively brought to a short boil), and is then lowered to somewhere between 109-115°F (42.8-46°C). This temperature favors ''Lactobacillus'', while discouraging Enterobacteriaceae. Optionally, the mash pH can be lowered to 4.4 with lactic acid or acidulated malt to further discourage Enterobacteriaceae activity. Once the desired temperature (and optionally pH) is reached, a handful of fresh malted unmilled grain is added to the mash and allowed a few minutes to inoculate the mash with the microbes found naturally on the grain husks. The wort is then transferred to a second vessel such as a glass carboy. The vessel should be filled to the very top, minimizing the oxygen levels inside the vessel. The vessel should be stored in a heated environment that maintains a temperature between 109-115°F (42.8-46°C) for 1 to 3 days depending on how much acidity the brewer wants (the faster the souring process the better; Jeff Young from Blue Owl achieves the desired acidity in about 18 hours usually) <ref name="young_grains"></ref><ref name="james_spencer">[http://beerandwinejournal.com/sour-wort-berliner/ Spencer, James. December 15, 2014. Beer and Wine Journal.] </ref>.
Once the 1 to 4 day time period has been reached, the wort is transferred to the boil kettle and boiled as normal. Boiling will kill all of the microorganisms in the wort, and will provide the option for adding hops and other kettle additions. Just as with kettle souring, the wort doesn't have to be boiled, but can be instead heat pasteurized at 170°F (76.6°C) for 15 minutes <ref name="pasteurization" />, or at 140°F (60°C) for 15 minutes if a yeast contamination produced a significant amount of alcohol. Once boiled or pasteurized, the wort can be chilled and handled in the same way as the above methods for wort souring.
[http://beerandwinejournal.com/sour-wort-berliner/ James Spencer provides an article] that fully explains his process, as well as a step by step video guide and tasting on Beer and Wine Journal <ref name="james_spencer" />.
===Tips on Maintaining Heat for Homebrewers===
Keeping the temperature as steady as possible for a pure culture ''Lactobacillus'' fermentation is not that important. Just try to stay in the range of the temperature best suited for a given species (see the [[Lactobacillus#Culture_Charts|''Lactobacillus'' culture charts]]). Here are some tips from MTF members on maintaining warm temperatures for sour worting <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1279628395398705/ Tips from many MTF members on maintaining heat for sour worting. 04/07/2016.]</ref>:
:''Editor's note: please be cautious when using heat sources to heat plastic fermenters; PET bottles have been known to melt or warp when applying too much heat to them.''
* For metal vessels such as a kettle, keep it on the stove burner and turn the burner on when heat is lost.
* Put the wort in a plastic bucket and seal with lead, then lower that bucket into a ten gallon water cooler and close the lid. Optionally, insulate with blankets.
* Use a glass carboy FermWrap™ heater attached to a sensor thermowell through the cap and a temperature controller.
* Use a Brew Belt Fermentation Heating Belt and wrap a "hoody" sweater or some other fabric around it to insulate, and a temperature controller.
* Use an aquarium heater (Enheim band recommended), fill a large plastic cooler with water and keep the water warm with the aquarium heater. Set the souring vessel in the cooler.
* Use an [http://anovaculinary.com/ Anova sous vide device] - place the vessel in a larger vessel with water, and keep the heat applied to the outside water with the Anova. Works well for maintaining heat for starters too.
* If not using a plastic vessel, keep the vessel in an oven (if it fits) or an electric smoker.
* Use a [http://www.amazon.com/Zoo-Med-Reptile-Cable-14-75-Feet/dp/B001OVBEEK/ref=sr_1_1?ie=UTF8&qid=1460052384&sr=8-1&keywords=zoomed+reptile+heat+cable ZooMed Reptile Heater Cable] inside of a fermentation chamber. Line the inside of the chamber walls with the wire and secure with duct tape.
* If maintaining heat is not possible with any of the techniques mentioned, use a species such as ''L. plantarum'' that produces acidity at room temperature. [[Lactobacillus#Omega_Yeast_Labs_on_OYL-605|Omega Yeast Labs OYL-605]] works well without hot temperatures.
===How to Pre-Acidify===
After the production of the wort, but before pitching the culture of ''Lactobacillus'', some brewers like to slightly lower the pH of the wort with food grade lactic acid (available at homebrew stores) or phosphoric acid before adding the ''Lactobacillus''. Acidifying the wort before pitching ''Lactobacillus'' has several benefits, such as discouraging unwanted microbes that may have accidentally been introduced into the wort, and helping to prevent [[Lactobacillus#Foam_Degradation|''Lactobacillus'' from degrading foam proteins]]. The idea is to get the wort down to a pH of 4.0 - 4.4 before adding ''Lactobacillus''.
There currently is no formula for how much lactic acid to add to a volume of wort due to the different buffering capacities of wort <ref>[http://www.mbaa.com/districts/Northwest/Events/Documents/Study%20in%20the%20Practical%20Use%20of%20Lactic%20Acid%20Bacteria.pdf A Study in the Practical Use of Lactic Acid Bacteria. Greg Doss from Wyeast Laboratories Inc. 2014.]</ref>. Water chemistry spreadsheets and formulas geared towards mash pH adjustments may not be accurate for wort pH adjustments since wort does not contain grain material, however there has been reports on MTF and recommendations from Martin Brungard (author of Bru'n Water) that [https://sites.google.com/site/brunwater/ Bru'n Water] can accurately determine how much lactic acid is needed to lower a wort's pH, or at least provide a starting point <ref name="delange_brungard"></ref>. We encourage readers to experiment with water chemistry calculators to see if they can accurate predict wort pH adjustments or get a starting point for how much acid to add <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1244954842199394/?comment_id=1245053585522853&comment_tracking=%7B%22tn%22%3A%22R%22%7D MTF Thread with Landon Ortiz. 03/03/2016.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1290987234262821/?comment_id=1353870694641141&reply_comment_id=1354548117906732&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Conversation with Adam Boura and Mark Trent on MTF regarding using Bru'n Water for adjusting wort pH. 07/18/2016.]</ref>.
Another method of finding out how much acid to add would be to pull a measured portion of the wort out, and add acid in measured amounts until the desired pH is reached. The amount of acid added can then be scaled up to the full volume of the wort. A.J. Delange suggests that the buffering capacity of wort might be half that of the mash (based on the kilograms of malt used in the mash) <ref name="delange_brungard">[http://www.homebrewtalk.com/showthread.php?t=587124 A.J. Delange. Homebrewtalk Thread. 07/19/2016.]</ref>.
Trial and error might be the most practical approach for homebrewers that don't have an abundance of wort to spare for finding out how much acid to add to a sample and scaling that up. Post boil, the wort pH is generally around 5.0 - 5.2. Adjusting the pH of wort before pitching ''Lactobacillus'' can then be done fairly easily by taking a trial and error approach. Using 1 mL of 88% lactic acid per .1 shift in pH for 5 gallons of wort is a good starting measurement. As an example, say that 5 gallons of wort has a pH of 5.0 just before pitching the ''Lactobacillus'' culture. Begin by adding 5 mL (1 US teaspoon) of food grade lactic acid to the wort for a target of ~4.4 pH. Stir gently, then take another pH reading. Continue to add 1-2 mL of lactic acid until the wort has the desired pH. Derek Springer has observed that it takes about one tablespoon (15 mL) of 88% lactic acid to reach a pH of 4.2 - 4.5 for 5 gallons of wort <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1290987234262821/?comment_id=1291031577591720&comment_tracking=%7B%22tn%22%3A%22R3%22%7D Conversation with Derek Springer on MTF regarding acidifying wort. 04/24/2016.]</ref>, however a higher amount may be required if the brewer's water is high in bicarbonate (24 mL for 5 gallons of wort to reach a pH of 4.4 was reported by Sean McVeigh for his water which contains 375ppm of bicarbonates <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1290987234262821/?comment_id=1291031577591720&reply_comment_id=1291118190916392&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Sean McVeigh on MTF on acidifying wort. 04/23/2016.]</ref>). Once a pH of 4.0 - 4.4 is reached, pitch the ''Lactobacillus'' culture. This small amount of lactic acid shouldn't have much of an impact on flavor. If a more precise method for determining the required amount of lactic acid is required, a sample of the wort can be pulled and lactic acid or phosphoric acid can be added to it until the target pH is reached, and then that amount can be scaled up (a micropipette might be required to measure very small amounts of lactic/phosphoric acid).
===Concerns about Dimethyl Sulphide (DMS)===
* See [[Dimethyl Sulfide]].
==See Also==
===Additional Articles on MTF Wiki===
* [[Sour Mashing]]
* [[Alternative Bacteria Sources]]
* ''[[Lactobacillus]]''
* [[Mixed Fermentation]]
===External Resources===
* [http://suigenerisbrewing.blogspot.com/2015/07/how-i-sour-mash-recipe.html "How I Sour Mash & A Recipe"; Sui Generis Blog (includes Sour Worting and microbiology information).]
* [http://www.fivebladesbrewing.com/year-sour-mash/ "Year of the Sour Mash" by Derek Springer. This series of articles were written for his NHC 2015 presentation.]
* [http://sourbeerblog.com/lactobacillus-2-0-advanced-techniques-for-fast-souring-beer/ "Lactobacillus 2.0 - Advanced Techniques for Fast Souring Beer", by Matt Miller of Sour Beer Blog.]
* [https://byo.com/stories/issue/item/3353-overnight-acidification "Overnight Acidification" by Michael Tonesmiere, article for Brew Your Own Magazine on Jan/Feb 2016.]
==References==
<references/>
[[Category:Techniques]]