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→Is There a List of Viable Bottles?
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 ~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.
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 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.
===Supplementing another fermentation===
* If the brewer wants to keep the dregs separate from other cultures or does not have another vessel available as previously described, leave the last quarter inch of the beer in the bottle itself. Recap the bottle if possible, and place it in the refrigerator. If it is not possible to recap the bottle because it is a corked bottle or a wider diameter than the brewer's bottle capper/caps, cover the bottle with plastic wrap or tin foil and a rubber band. Keeping the beer cool should prevent spoilage, although this is not guaranteed without more sanitary procedures such as purging the bottle with CO2 and capping it. Although brewers have successfully stored bottle dregs beers like this for months, it is generally advisable to make a starter for the dregs at least within a few weeks so as to avoid any potential spoilage.
* ''Brettanomyces'' remains more viable over time if it was co-fermented with ''S. cerevisiae'' than if it was fermented by itself ([[100%25_Brettanomyces_Fermentation|100% ''Brettanomyces'' beers]]). Contrarily, ''S. cerevisiae'' loses viability over time faster when it is co-fermented with ''Brettanomyces'' <ref name="Hubbe">[https://www.facebook.com/groups/MilkTheFunk/permalink/1407620509266159/ Effect of mixed cultures on microbiological development in Berliner Weisse (master thesis). Thomas Hübbe. 2016.]</ref>. This is something to keep in mind when using dregs.
===Dregs From Natural Wine===
Since natural wines are spontaneously fermented and often contain lower amounts of sulfite or no added sulfite, some beer brewers have attempted using the bottle dregs from commercial natural wines. See [https://www.facebook.com/groups/MilkTheFunk/permalink/3645548365473351/ this MTF thread] for experiences doing this.
==Potential Problems and Issues==
===Is There a List of Viable Bottles?===
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.
==See Also==