13,691
edits
Changes
m
no edit summary
* [http://suigenerisbrewing.blogspot.ca/2014/12/two-new-videos.html Sui Generis Blog] video tutorial for catching wild yeast from fruit or from the air.
* David Thornton of [[SouthYeast Labs]] describes his favorite method of catching wild yeast/bacteria: "Most of our cultures are taken from over ripened fruit macerated in its own juice and left to ferment 24 hours at the location in a small erlynmeyer with a perforated cap. Always grows something, and almost always get an alcohol fermenting strain, and of the alcohol fermenting strains id say 10% are worth brewing with. I like this method because I can stir my loop and do a streak on regular UBA aerobically, then pull favorable looking colonies for yeast and lacto and do a quadrant streak on selective media for isolation." <ref name="Thornton">[https://www.facebook.com/groups/MilkTheFunk/permalink/1141930175835195/?comment_id=1142286619132884&reply_comment_id=1142394019122144&total_comments=4&comment_tracking=%7B%22tn%22%3A%22R6%22%7D Conversation with David Thornton on MTF. 09/06/2015.]</ref>
* Monitor for mold growth. If mold begins to grow on the growth media, scrape it out and continue on with the isolation process. This should be safe since isolating the yeast will separate it from any potential mycotoxins that developed during the initial catching. Do not consume any growth media that has had mold grow on it (see [[Mold]]).
===Isolating===
==Growing and Testing Without Plating==
While using agar plates to isolate yeast colonies is the most effective way to culture wild yeast, it is not the only way. Wild yeast should first be caught using DME wort as outlined in [http://bootlegbiology.com/diy/capturing-yeast/ Bootleg Biology's ''Method 1'' or ''Method 2'']. Hopping the wort will help decrease bacteria if that is desired. The wort's pH should be lowered to 4.5 or lower with lactic acid to avoid bacteria as much as possible. Molds may still grow in the yeast starter even with the lower pH, and ; wort that has grown mold should not be removed by scraping them off of consumed because mycotoxins can contaminate the surface of wort (see [[Mold]]). If the yeast cannot be isolated from wortthat mold grew on then it should be thrown out. Signs of a small krausen within 1-3 days is a good sign that viable wild yeast has been collected. After another few days, the yeast will start dropping to the bottom of the collection vessel <ref name="manoaction">[http://www.homebrewtalk.com/collecting-wild-yeast.html Collecting Wild Yeast. Manoaction. Homebrewtalk. Oct 30, 2012.]</ref>.
Once the wort has fermented out (allowing 2 weeks total is a good rule of thumb), decant the beer and pitch the collected yeast into 500ml of starter wort, again lowering the pH of the starter wort to 4.5 with lactic acid. After the starter wort has been fermented, the yeast should have enough of a population to ferment out a 1 gallon batch of wort. Keep the recipe of the wort simple, and in the 1.050 gravity range. The yeast cell count should be high enough at this point to out-compete bacteria, and lower the pH of the wort within a few days. The pH of the 1 gallon batch therefore does not need to be lowered, although the brewer may choose to do so anyway. For [[Wild_Yeast_Isolation#Safety|safety reasons]], test to make sure that the beer fully attenuated and has a pH of 4.5 or less. Allow for one month after fermenting the 1 gallon batch of beer before sampling. If it smells like feces or vomit, do not sample it and throw it away. If the beer smells ok, feel free to sample the beer to see if the wild yeast produced a good tasting beer. David Thornton from [[SouthYeast Labs]] estimates that only about 10% of yeast that can fully attenuate produces favorable results, so failures are to be expected (keep trying!) <ref name="Thornton"></ref>. Fermenting a few batches of beer at different temperatures is a useful method for identifying the ideal fermentation temperature range for the yeast.
* See [[Mold]] for safety identifying mold and safety issues with mold.
===Safety===
* See also [https://www.facebook.com/groups/MilkTheFunk/permalink/1447181778643365/?match=Ym90dWxpc20%3D this MTF thread on the mechanisms of botulism poisoning, and how it applies to different brewing processes].
* [https://suigenerisbrewing.blogspot.com/2017/01/fact-of-fiction-can-pathogens-survive.html Further explanation of what makes microbes "pathogenic" by Bryan from Sui Generis Blog] and a related [https://www.facebook.com/groups/MilkTheFunk/permalink/1246624848699060 MTF discussion].
* If mold grows on growth media and the yeast can be isolated cleanly, then this is not an issue. If the yeast is not being isolated on agar plates, then throw out the capture sample and do not use it. See [[Mold]] for identifying mold and safety issues with mold.
==Wild ''Brettanomyces''==