Wild Yeast Captures

We're big fans of mixed culture brews of all kinds, but the most enticing and exotic feature yeast and bacteria not grown in labs. These beers utilize wild or native cultures unique to their location/terroir. Breweries such as Jester King, De Garde, Logsdon, and Russian River have been experimenting with spontaneous fermentation in the United States for years. The most famous wild ales, however, are the Lambic and blended Geuze from Belgian brewers such as Boon, Drie Fonteinen and Cantillon.

The idea of utilizing a native yeast for an Oakland inspired saison has been rattling around our brains for a bit. So... after utilizing bottle dregs from some our favorite sour brewers for some one gallon experiments, we decided to (attempt to) capture a native Saccharomyces strain.

Capturing yeast isn't as easy as leaving some wort out overnight. Well... actually... it can be. This method, however, will also encourage all kinds of bacteria that you aren't necessarily looking for. Since I am not looking to brew a lambic-style beer aged over multiple years, I decided to do my best to avoid capturing any enteric bacteria (such as salmonella). This type of bacteria is very dangerous early in fermentation but serves as a precursor for later yeast/bacteria cultures over very long fermentation.

After doing some research on Milk The Funk and Bootleg Biology we reached out to Nick over at The Yeast Bay for some advice how we might increase our odds of successfully capturing what we were looking for. Using his advice we made a 1.030 wort and pre-acidified using lactic acid. We also used grain alcohol (vodka) to keep the wort at approximately 1% abv. Saccharomyces cerevisiae (brewers yeast) is moderately tolerant to both alcohol and acidity while many other types of yeast and bacteria are unable to reproduce in such conditions.

Once we had our wort boiled, pre-acidified, and alcohol added we scrubbed some mason jars and sprayed them with sanitizer (Starsan) and put on their lids. We headed out to the Oakland hills and gathered a variety of wild flowers, weeds, and grasses. We returned home to add the wort and shortly thereafter realized a few mistakes we had made. We will get to those in just a moment.

At home we placed airlocks on some handy pickling lids (fitted to screw on to mason jars with a whole drilled out and gasket in place) onto the samples and placed them in a closet.

After a week we saw mold forming. Although there is still a possibility of collecting viable yeast from these samples, there is an increased risk of mycotoxins being present in the liquid. After smelling two of the samples (purple wild flowers and dry grass) we decided to dump them. A third sample containing a dandelion-like weed had a pleasant aroma that we want to hold on to. Using a sanitized spoon we removed the plant matter and mold growing on the surface. Our plan is to step up this sample and get it over to The Yeast Bay for analysis if it continues to display pleasant aromas.

So what did we do wrong? What could we have done better?

- We didn't add hops to the starter wort
Hops and their various oils will tame lactic acid producing bacteria (Lactobacillus). Our goal was to capture a saccharomyces strain so this is just one additional step along with the pre-acidification and alcohol we should have utilized.

- We didn't boil the wort long enough
Upon putting the starter wort over the plants we collected, we noticed a layer of sediment form very quickly. This leads me to believe the dry malt extract we used had not fully dissolved and incorporated into the water. A longer boil will be used next time.

- We didn't chill the wort
Once the wort was boiled and additions were made (lactic acid and alcohol), we left the pot to cool on its own while we left to gather the plants. On a normal day this may have been enough to cool the wort to a pitchable temperature. However... this was during a heatwave and the ambient temperature of the kitchen where the wort was prepped never cooled down. Once the wort was added we noticed how warm it still was. There is a strong likelihood that much of the viable yeast on the plants was killed on upon contact with the warm wort.

- We left too much headspace
Mold, although not rare in wild captures, adds substantial risk to being able to isolate a viable sample. These types of mold are typically aerobic and enjoy access to oxygen. Next time we plan on filling the jars much higher with less headspace for less oxygen.

- We didn't remove the plants
Any part of a fruit, vegetable, flower, etc that sits above the surface of the starter wort is going to encourage mold growth. Next time we will likely remove any solids after 48 hours, allowing any yeast enough time to inoculate the starter wort but not long enough for mold spores to get a strong start.

Despite our mistakes we had a great time and we look forward to our next attempt. Wish us luck!