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Any commercial (and homebrewed) sour/wild/funky beer can be used to inoculate another beer and/or wort as long as it is not kettle soured or pasteurized. Dregs can be used from many types of sour/wild/mixed fermented commercial beers (as long as they are not kettle sours or pasteurized), including [[Mixed_Fermentation|mixed fermentation]] sour beers where the microbes that the brewery used are from a yeast lab, wild-fermented beers that use [[Wild_Yeast_Isolation|wild-caught or bioprospected microorganisms]], Belgian [[lambic]] and non-lambic sour beers that are [[Spontaneous_Fermentation|spontaneously fermented]] in a coolship, beers that are co-fermented with [[Brettanomyces_and_Saccharomyces_Co-fermentation|''Saccharomyces'' and ''Brettanomyces'']], etc. The instructions on this wiki page apply to all of these types of beers (in other words, spontaneously fermented beers don't need to be treated differently than mixed fermentation beers using lab yeast/bacteria).  Generally, only the last half inch of a bottle's contents, including the sediment, is used. This portion of the beer is often referred to as "the bottle dregs". It is recommended that the microbes in the beer are first reinvigorated with a small starter wort of around 1.030 gravity before it is added to the fermentation vessel. A fresh pitch of regular brewers yeast is often advised to use along with the dregs, but this is not always a requirement if the commercial beer still has viable ''Saccharomyces'' yeast in it. Using commercial sour beers to ferment is generally a good idea because the microbes are often stronger and more aggressive from commercial breweries as compared to mixed cultures from yeast companies (this is a generalization; smaller and more specialized yeast labs offer very aggressive alternative yeast and bacteria strains). It is generally advised to use as fresh of a bottle of commercial sour beer as possible, however, older bottles can be used as well depending on the brewery, the microbes in the beer, and how the bottle was stored.

The following information is specific to collecting microbes from commercial bottles of mixed fermentation sour beers or ''Brettanomyces'' beers. For instructions on collecting ''S. cerevisiae'' from clean beersthat only contain this species of yeast and no other microbes, check out [https://www.jaysbrewing.com/2012/09/05/9-steps-to-culture-yeast-from-a-bottle/ this guide].

An often asked question in the Milk The Funk Facebook group is whether or not dregs should be added to a [[Wort_Souring#Souring_in_the_Boiler_.28Kettle_Sour.29|kettle sour]]. While there is no reason why it wouldn't produce a good beer (assuming the dregs are in good health), it defeats the purpose of making a kettle -soured beer. The primary advantage to kettle souring is the ability to make a sour beer without risking exposing the brewer's cold side equipment to potential brewery contaminants such as ''Brettanomyces'' and lactic acid bacteria.

After prolonged time in a bottle, microorganisms won't be at their peak vitality, and so making a starter for dregs is recommended in general. ''Saccharomyces'' strains may or may not be viable at all after an extended time in a low pH beer, but ''Brettanomyces'' and some lactic acid strains are more acid-tolerant and should be viable. Making a "step" starter is the best practice for ensuring that a high enough population of microbes are pitched. Begin by making a ~200 100 mL DME starter of usual strength (1.030-1.040 SG) <ref name="preiss">[https://www.facebook.com/groups/MilkTheFunk/permalink/1268830686478476/?comment_id=1269605776400967&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Richard Preiss on step starters for dregs on MTF. 03/27/2016.]</ref>. Hops should not be used unless the brewer wants to try and suppress the ''Lactobacillus'' in the commercial beer (''Lactobacillus'' strains for some commercial breweries are fairly hop tolerant up to 20-25 IBU. See [[Lactobacillus#Hop_Tolerance|Lactobacillus Hop Tolerance]] for more information). If the brewer has only one bottle or wants to keep multiple bottle dregs separate from each other, the starter wort can be poured directly into each bottle and covered with plastic wrap. Alternatively, the dregs from multiple bottles can be combined into a single vessel (such as an Erlenmeyer flask or glass jug) with the starter wort, and covered with sanitized tin foil to allow an exchange of oxygen and CO2. The mouth of the bottle may be flamed with a lighter to kill any wild yeasts that might have landed on the area. The dregs don't need to be "washed" or treated in any special way before being added to the starter wort.

Although more experiments are probably needed, agitation is believed to Agitation can be an important factor for any species of microbe (yeast and bacteria). Gentle stirring on a stir plate or orbital shaker, or frequent gentle manual agitation leads to faster growth and a higher number of organisms. Agitation keeps the microbes in solution. It also maximizes the microbes' access to nutrients and disperses waste evenly. In a non-agitated starter, the microbes are limited to the diffusion rate of nutrients, leading to a slower and more stressful growth <ref name="BryanHeit_starters">[https://www.facebook.com/groups/MilkTheFunk/permalink/1168024059892473/?comment_id=1174865305875015&reply_comment_id=1176092372418975&total_comments=1&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Conversation with Bryan of Sui Generis Blog about starters and agitation. 11/09/2015.]</ref>. Allowing for at least some oxygen to enter the vessel will help ''Brettanomyces'' grow, and limiting oxygen will help any surviving ''Saccharomyces'' to grow. For more information regarding aeration and agitation effects on ''Brettanomyces'' growth, see [[Brettanomyces_Propagation_Experiment|Mark Trent's Brettanomyces Propagation Experiment]] and [[Mixed_Cultures#Effects_of_Mixed_Cultures_on_Growth|Effects of Mixed Cultures on Growth]].

The starter should be stored at room temperature for at least 5-7 days and sometimes longer if growth does not occur within that time. It can be stored at a higher temperature if bacteria is the main microbe that the brewer is after, although avoid going above 86°F/30°C. Monitor the starter for activity during this time to ensure that there are viable microbes. Visual activity may not always be present, may be brief, or minimal. Visual indicators of successful growth include turbidity and continuously produced bubbles on the surface of the liquid. Monitoring the pH and the gravity can assist the brewer with deciding whether or not the commercial sour beer has any viable microorganisms still alive in it. If mold grows in the starter, it should be discarded and not used (see [[Mold]]). If the starter krausens within 2-3 days then it might have viable ''Saccharomyces'', otherwise strains of ''Saccharomyces'' might be dead (especially if the beer was not freshly bottled and was a low pH sour beer; see [[Commercial_Beer_Dregs_Inoculation#The_Dreaded_Killer_Champagne.2FWine_Yeast|"Dreaded Killer Champagne/Wine Yeast" below]]). ''Brettanomyces'' may not show signs of fermentation for up to 3-7 days (in some cases and depending on the viability of the microbes, signs of growth may not appear until up to 2 weeks). Once the starter starts showing signs of fermentation, it should be aged for another 3-7 days to finish fermentation. After the fermentation starts to slow, create a another 1 liter starter of DME wort, and add the original 200 100 mL dregs starter to it. Repeat the process above, giving the 1 liter starter another 5-7 days of growth <ref name="preiss"></ref>. Pitch the 1 liter starter into a ~20 liter batch, or continue to step up the starter for larger batch sizes. Avoid storing the starter for extended amounts of time because a low pH could result in lower viability over time in an acidic environment; see [[Mixed_Fermentation#Storing_a_Yeast_Cake_or_Sample|Storing a Yeast Cake]] and [[Mixed_Cultures#Starters_and_Other_Manufacturer_Tips|Mixed Culture Starters]] for more information.

In general, almost all craft breweries do not pasteurize their mixed fermentation sour beer products. A few examples that do include New Glarus, New Belgium's sour beers prior to 2018 <ref>[https://beerandbrewing.com/the-best-18-beers-of-2018/ "The Best 18 Beers of 2018". Craft Beer and Brewing Magazine. Jamie Bogner , John Holl Oct 19, 2018.]</ref>, some [https://www.lambic.info/index.php?title=Special%3ASearch&profile=default&fulltext=Search&search=pasteurized Belgian lambic based beers (gueuze, kriek, framboise, and faro)], and most [[Flemish_Red-Brown_Beer|Belgian Flanders Red Brown beers]]. The only list of viable commercial bottles that we know of is [http://www.themadfermentationist.com/p/dreg-list.html Michael Tonsmeire's list of unpasteurized commercial sour beers.] Tonsmeire has stated that he will no longer maintain this list because of the effort needed to do so. For this reason, we also do not track unpasteurized commercial sour beers. If you are curious if a particular brewery pasteurizes or kettle sours their sour beer, it is recommended that you contact the brewery and ask them if the bottles dregs can be used to make sour beer. Most breweries will be friendly enough to answer your question.