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# After the 24-48 hours, decant and discard the liquid and leave the biomass at the bottom. Add 75 mL of new starter media to the flask (with the biomass still at the bottom of the flask) that is 8-10* Plato with yeast nutrient, and purge the flask with CO2. Put an airlock on it on a stirplate and grow until the sugars have fermented.
# Again, decant and discard the liquid and leave the biomass at the bottom of the flask. Purge the flask (with the biomass still at the bottom) with CO2, and add 75 mL of 20° Plato wort with yeast nutrient and an airlock, and place on a stirplate or shaker. Look for the wort to ferment down to around 2 Plato or so.
# After the 20° Plato wort has finished fermenting, samples from the liquid (the liquid contains the more active yeast versus the biomass at the bottom of the flask) are streaked onto media to isolate the strains that have survived. If agar plating is not an option, a less advanced approach can be taken by [[Wild_Yeast_Isolation#Growing_and_Testing_Without_Plating|growing and testing without plating]].
Agar that David uses (see also [[Laboratory_Techniques#Growth_Media|Growth Media]] on the wiki for other media types that might also be useful):
==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/ one of Bootleg Biology's methods] or [[Wild_Yeast_Isolation#David_Thornton.27s_.22Yeast_Bootcamp.22|David Thornton's Yeast Bootcamp method]]. 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; wort that has grown mold should not be consumed because mycotoxins can contaminate the wort (see [[Mold]]). Keeping the foraged fruit, flowers, etc. under the surface of the wort will help reduce the chances of mold growth. Some brewers recommend submerging the fruit/flowers in the wort for a few minutes and then removing them to prevent them from attracting mold growth <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1659565197405021/?comment_id=1711116612249879&comment_tracking=%7B%22tn%22%3A%22R%22%7D Jeff Porn. Milk The Funk Facebook group. 06/06/2017.]</ref>. If the yeast cannot be separated from wort that 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.