Editing Kettle souring

[[Category:Wort production]] [[Category:Fermentation, packaging, and storage]]
"Kettle souring" is a method of creating [[sour beer]]. It is a form of pre-souring — souring the wort before [[yeast fermentation]]. Souring is achieved by adding [[lactic acid bacteria]] (most often ''Lactobacillus'') to the wort in the kettle, allowing the bacteria time to create [[lactic acid]], and then boiling before the subsequent yeast fermentation. This process is designed to avoid possible contaminants from coming into contact with [[cold-side]] equipment.

We consider kettle souring to be an antiquated process without any benefits compared to [[sour beer|modern souring methods]].<br />
See here: [[Sour_beer#Comparison_with_other_souring_methods | Comparison of fast souring methods]].

'''Pre-sour method''' (kettle souring):
# Make unhopped wort.
# Optional/recommended: Bring the wort to boiling temperature for up to 10 minutes.
# [[wort chilling|Chill]] the wort to 100°F (37°C) or less.
# Optional/recommended: Pre-acidify the wort to between [[pH testing|pH]] 4.0-4.5 (measured at room temperature), which helps with [[head retention]] and helps avoid growth of certain contaminating microbes.
# Pitch the bacteria.
#* A very high pitch rate is recommended, preferably using a [[sour beer#Lactobacillus_starter|Lacto starter]].
#* ''[[sour beer#The_Bacteria|L. plantarum]]'' and ''L. brevis'' are the preferred species.
# Seal the kettle to prevent airborne contaminants from getting into the wort.
#* With good sanitation, pre-acidification, and pre-boiling, it is not necessary to "purge" with CO<sub>2</sub>.
# Allow it to sour for 12-48 hours.
#* ''L. plantarum'' requires maintaining temperature above 70°F (21°C). Higher temperatures up to 98°F (37°C) will speed up souring.
#* Other ''Lacto'' species require maintenance of a higher temperature (refer to recommendations for the particular culture).
# Optional/recommended: Monitor [[pH]]. Generally the target pH is within 3.1 to 3.8.
# Optional/recommended: Measure [[specific gravity]] after souring. If the s.g. drops more than a couple points, that's a sign of yeast contamination.
# Boil the sour wort as normal, adding any [[hops]] desired. Alternately, the wort may be brought up to 180°F (83°C) to pasteurize.
# Chill and aerate as normal.
# Higher yeast pitch rate is recommend because lactic acid inhibits yeast growth.
#* Dry yeast should be [[rehydrated]] before pitching.
#* Liquid yeast should be pitched from a [[starter]].
# Ferment and [[package]] as normal.

==The Good==
The kettle souring process can be used to make a particularly flavorless sour beer to serve as a base for other flavor adjuncts. It can also be a useful method if you cannot obtain ''L. plantarum'' and don't want to risk using a more hop-tolerant species on your cold-side gear.

Kettle souring is purported to reduce the risk of contaminating future clean beers. That is only true if you use wild microbes or a very hop-tolerant Lacto species as your bacteria culture. However, when using ''L. plantarum'' for souring, there is NO risk of cross-contamination even if it is used in cold-side equipment (i.e. not kettle soured).
* ''L. plantarum'' is extremely hop-sensitive, meaning that it will have no effect on any beer with hops.
* ''L. plantarum'' is easy to remove with normal [[cleaning]] and [[sanitation]] processes.

==The Bad==
Pre-souring and then boiling has notable effects on the resulting beer:
* Boiling the wort after souring removes the large majority of flavor compounds produced by the bacteria (besides lactic acid).<ref>Dvysik, A., et al. [https://onlinelibrary.wiley.com/doi/abs/10.1002/jib.569 "Pre-fermentation with lactic acid bacteria in sour beer production."] ''Journal of the Institute of Brewing,'' vol. 125, no. 3, 2019, pp. 342-356.</ref>
* The low pH environment inhibits ester production by yeast, greatly limiting any yeast flavor contribution.<ref>[https://open.spotify.com/episode/6Wr1AMrs5OspWpwl5Mh6fc "Episode #004 - Kettle souring with Adi Hastings from Omega Yeast Labs"] Milk the Funk podcast. 2018.</ref><ref>[https://open.spotify.com/episode/7D3LaDgmUVICWnTEQnr7jg Episode #007 - Lactobacillus microbiology with Dr. Bryan Heit of Sui Generis Brewing blog] (1 hour 37 minutes in) Milk the Funk podcast. November 2018.</ref><ref>[https://open.spotify.com/episode/2owYcSFS1rlT6JMMll8zYf Episode #008 - Mixed Fermentation 101 with Devin Bell of Cash Crop Brewery and Brandon Jones of Yazoo Brewing Co.] (1 hour 23 minutes in) Milk the Funk podcast. April 2019.</ref>

This combination of factors often results in a "one note" sour beer without any complexity.<ref>[https://open.spotify.com/episode/2SMUAet0PynDEECHtOar80 "Episode #006 - The history and resurrection of traditional German Berliner Weisse with Benedikt Koch of wilder-wald.com."] Milk the Funk podcast. 2018.</ref> This lack of flavor is considered undesirable by most craft beer drinkers.

Furthermore:
* The kettle souring process (described above) is much more complicated than [[sour beer|other souring methods]].
* Kettle soured beers take a couple days longer to produce due to the separate souring phase and longer fermentation (from the acid inhibiting the yeast).<ref>[https://www.reddit.com/r/Homebrewing/comments/ilppsg/kettle_sour_lag_time/ Kettle Sour Lag Time.] Reddit website. 2020. Accessed November 2020.</ref>

==The Ugly==
[[File:Kettle-sour-mold.jpeg|thumb|Mold on a kettle sour]]
During the pre-souring phase (in the kettle), the wort is particularly vulnerable to contamination. Unhopped wort is an excellent growth medium for wild microbes &mdash; it easily becomes contaminated and sometimes ruined during this phase of the process.

Contaminated kettle sours are common. Here are some examples:
*[https://www.homebrewtalk.com/threads/is-it-yeast-contamination-during-kettle-souring.675976/ Is it yeast contamination?(during kettle souring)] HBT thread
*[https://www.homebrewtalk.com/threads/pellicule-in-my-sour-kettle.669652/ Pellicule in my sour kettle??] HBT thread
*[https://www.homebrewtalk.com/threads/white-film-on-1-gallon-all-grain.668120/ White film on 1 gallon all grain?] HBT thread
*[https://www.homebrewtalk.com/threads/fixing-a-kettle-sour-with-a-yeast-infection.669655/ Fixing a kettle sour with a yeast infection...] HBT thread
*[https://www.homebrewtalk.com/threads/lacto-kettle-sour-yeast-contamination.649887/ Lacto Kettle Sour Yeast Contamination] HBT thread
*[https://www.homebrewtalk.com/threads/saving-a-kettle-sour.661537/ Saving a kettle sour] HBT thread
*[https://www.homebrewtalk.com/threads/kettle-sour-surprise-low-gravity.650504/ Kettle Sour (surprise! low gravity)] HBT thread
*[https://www.homebrewtalk.com/threads/1st-kettle-sour-spoiled.653546/ 1st kettle sour spoiled?] HBT thread
*[https://www.homebrewtalk.com/threads/goodbelly-ate-insane-amount-of-sugar.660229/ goodbelly ate insane amount of sugar?] HBT thread
*[https://www.homebrewtalk.com/threads/everyone-throw-your-ideas-on-maintaining-a-lacto-temp-on-a-kettle-sour-please.645740/post-8229219 Everyone throw your ideas on maintaining a lacto temp on a Kettle sour please!] HBT thread
*[https://www.homebrewtalk.com/threads/kettle-sour-infection-question.635476/ Kettle sour infection question] HBT thread
*[https://www.homebrewtalk.com/threads/60-hours-since-yeast-pitch-and-nary-a-bubble.633454/ 60+ hours since yeast pitch and nary a bubble] HBT thread
*[https://www.homebrewtalk.com/threads/kettle-sour-issues.586114/ Kettle Sour Issues] HBT thread
*[https://www.homebrewtalk.com/threads/bad-smell-with-omega-yeast-labs-lacto-starter.568170/ Bad smell with omega yeast labs lacto starter?] HBT thread
*[https://www.homebrewtalk.com/threads/what-in-the-world-took-over-my-kettle-sour.662170/ what in the world took over my kettle sour?] HBT Thread
*[https://www.homebrewtalk.com/threads/kettle-sour-probably-got-infected-with-yeast-what-to-do.657395/ Kettle sour probably got infected- with yeast. what to do?] HBT thread
*[https://www.homebrewtalk.com/threads/post-your-infection.71400/page-76#post-7395104 Post your infection] HBT thread
*[https://www.homebrewtalk.com/threads/white-labs-lacto-brevis.490829/ White Labs Lacto Brevis] HBT thread
*[https://www.homebrewtalk.com/threads/question-on-my-kettle-sour-fermenting-with-the-lacto.643351/ question on my kettle sour, fermenting with the lacto] HBT thread
*[https://www.homebrewtalk.com/threads/berliner-weisse-butyric-acid.645657/ Berliner Weisse - butyric acid] HBT thread
*[https://www.reddit.com/r/Homebrewing/comments/5xceb8/what_to_do_with_a_kettle_sour_contamination/ What to do with a kettle sour contamination?] Reddit thread
*[https://www.homebrewtalk.com/threads/sour-beer-wort-smells-bad.686765/ Sour beer wort smells bad] HBT thread
*[https://www.reddit.com/r/Homebrewing/comments/91n44y/first_kettle_sour_how_bad_is_the_smell_supposed/ First kettle sour, how bad is the smell supposed to be?] Reddit thread
*[https://www.reddit.com/r/Homebrewing/comments/71ewrk/kettle_sour_dumper_batch/ Kettle sour dumper batch] Reddit thread
*[https://discussions.probrewer.com/forum/probrewer-message-board/brewing-process-and-theory/process-and-techniques-sponsored-by-cpe-systems/50265-kettle-sour-gone-wrong Kettle Sour gone wrong] ProBrewer thread
*[https://www.homebrewtalk.com/threads/berliner-vomit-dump-or-reinfect.586039/ Berliner vomit: dump, or reinfect?] HBT thread
*Etc. Hopefully that's enough examples to make the point.

==See also==
* [[Sour beer]]
* Milk the Funk [http://www.milkthefunk.com/wiki/Wort_Souring Wort Souring] wiki article
* Matt Miller's [http://sourbeerblog.com/lactobacillus-2-0-advanced-techniques-for-fast-souring-beer/ Lactobacillus 2.0 – Advanced Techniques for Fast Souring Beer] blog entry

==References==