Yeast can be the difference between a good recipe and a great recipe. I have been making cider, wine and mead for over a year now and I am learning quite a bit about the strains out there and what they can bring to the table. While experimenting with the prominent strains found at my local home brew shop is fun and rewarding, I wanted to go one step further.
My supervisor at work (I work at a craft brewery), who happens to be my source for all my information involving fermentation, was telling me about Lambic style beers and how they use wild yeast and spontaneous fermentation to achieve their goals. This got me thinking about how I could try this in my tiny “office” at home.
I researched ways in which people collect wild yeast. Most of what I found was for bread making purposes, but I did find out that raisins are a common source for natural occurring yeast. And that they are very high in natural sugars making them an ideal candidate for this experiment
Looking into raisins and other fruits, I found that often dried fruits are sulphited to eliminate bacteria and of course this would kill off the yeast I am trying to culture. So I had to be sure to get dried fruits that have no sulphites in the ingredients. The bulk food chain I used lists any and all ingredients including sulphites, sulphur dioxide, oils etc…
I decided upon four different fruits, because I happened to have four mid-sized mason jars handy. I decided to go with Jumbo Flame Raisins, Medjool Dates (which I de pitted), Goji Berries, and Bing Cherries. I chose these four because they were of course unsulphited and had no added sugars. I wanted the purest form of the fruit possible.
Once home with my fruit choices I had to make a nice environment for my yeast to grow in. Using a medium sized pot I brought tap water to a simmer and let stand at that temperature for a few minutes before turning off the stove and letting cool to room temperature. I did this to help eliminate any chlorine in the water, as my city’s tap water is pretty bad sometimes. Once the water was at a workable temperature I poured one cup into each sanitized Mason jar, added one tablespoon of dextrose and one eighth teaspoon of yeast nutrient. Because this is an experiment, these volumes are strictly a guess, but I figure it is a good starting point.
With my growth environment already rich with sugar and nutrient it was time to add the fruit, one quarter cup of each fruit was put into its own jar. The dates were pitted and chopped roughly, the cherries were also chopped. Once each jar was sealed I gave them all a quick swirl to get things moving. I noted that three out of the four fruits sank immediately, only the goji berries remained floating.
Dried Fruits Used Should Not Have Sulphites
Day two I opened the jars for a moment, long enough to give each one a swirl to introduce a little oxygen into the mix. Leaving them in a nice warm area of my apartment I went to work. After coming home I noticed the dates and the goji berries both had a small amount of bubbles forming on the outside edge of the jar. Looking a little closer it almost looked like krausen had formed on the goji berries, while the raisins and cherries remain unchanged other than the colour of the water. Shining a light into the two that seemed to have some activity, I could see tiny bubbles rising to the surface, so I opened them just slightly. The goji berry jar let out a hiss of CO2. I achieved fermentation in approximately 30 hours.
Fermentation In Approximately 30 Hours
Raisin Fermentation By Day Three
The third day in this mad science experiment, the raisins which had been pretty lifeless thus far have all risen to the top of the water, and there are quite a few bubbles sticking to each one. Yet another jar beginning its fermentation journey.
By Day Four All Fruits Were Fermenting Nicely
Day four the cherries have joined the other three fruits and started to bubble. All four of the jars had to be opened because there was a co2 build up in the jar. All four gave a pleasant hiss when they were loosened.
The raisins seem to be picking up speed, and are doing better than the other three. Although it took 3 days to get started, and only one day for the goji berries and the dates, the amount of fermentation going on in the raisin jar is substantially higher.
On day five the fermentation in the cherries and raisins had seemed to begin to slow. The goji and dates had already slowed their bubbling so I decided to move onto phase two of the experiment.
I separated the fruit from the liquid and drained approximately half of the remaining liquid off. I used what was left to swirl the yeast into suspension and poured them each into their new fermenters. Each one was put into a litre of sugar water with a gravity of 1.045, and tsp. of nutrient was added. The new fermenters were placed back where the original mason jars were kept.
Secondary Fermentation Produced Lots Of Yeast
A couple days into their second ferment, and they all were doing well. The cherries seemed to be doing the best with a nice yeast cake forming on the bottom. Each one is bubbling away at a good pace. Further, they all have some krausen on the top; the Goji has almost 3 inches of it. They remained in these fermenters for 5 days in total.
The last step I took was to rinse and separate the yeast. I first allowed it to settle and form a nice layer on the bottom of the vessel. I racked off the liquid and transferred the remaining yeast back to the mason jars with some distilled water. That sat for about 4 hours, and then I carefully sucked up the water with a turkey baster, leaving as little liquid as I could. Another small splash of distilled water to get the yeast back into a suspension and I transferred one final time into their small containers to be stored in the fridge.
Final Results Lots Of Free Wild Yeast
The final result is a nice little yeast supply cultured in my own make shift lab.
Experiment by adding fresh, in-season berries or flowers to 250 to 500 milliliters of unhopped wort. If you want to harvest only yeast, Crowell says, add some hops with 20+ IBUs to the wort to prohibit bacterial growth. When culturing this yeast, try curing part of the yeast exposed to ambient air and part of it without oxygen. Let some wort ferment with native yeast and bacteria and let some ferment with a mixture of native yeast and lab-cultured strains of Saccharomyces. These various trials will serve, quite literally, as litmus tests for finding desirable flavor profiles in beer. “This method will vary, as we’ve repeated it with other types of flowers and berries with no success,” says Crowell. “The biggest secret to embracing your local flora is patience.”
In Wild Brews (Brewers Publications, 2005), Jeff Sparrow has a few more recommendations for homebrewers hoping to embrace their backyard microflora. The first is to find a source of wild yeast (e.g., fruit trees or a nearby orchard). The more windy the climate, the more likely the yeast and bacteria in the air are to find your wort. He also suggests surrounding your fermentation room with porous wood and even splashing some live beer, such as gueuze, around the fermenting beer. “The presence of beer in a room should eventually induce the ‘permanent’ growth of various beer-fermenting and beer-souring microorganisms. . . . The more beer fermented in the space, the more microorganisms will produce in and around the beer.”