Yeast spores are all around us. Suppose there was no access to commercial yeast, and you wished to make bread and/or beer (i.e. in some post-Apocalyptical world). Are there any problems in collecting wild yeast spores? Commercial yeast will probably be far better to use, but are there going to be any toxic products created by wild yeast?
I know that the collection can be done in principle (sourdough breads, ancient bread and beer recipes etc.) How would you collect the yeast (from the surface of fruits?)? How would you culture it? How would you recognise that the culture you have is yeast and not some deadly e-coli bacterium, for instance?
Well, in a sourdough, you just take flour (usually rye to begin with), mix with water, and the yeasts that are present in the milled flour (not wild ones in the air, as Alton Brown likes to explain), feed off the flour, reproduce, and fart, producing carbon dioxide bubbles. Just keep adding more flour and water, and the yeast will get stronger and continue to reproduce until you have enough to leaven bread. I believe the high pH of sourdough starter inhibits bacterial growth, but I’ll need someone else to chime in on that.
You could accumulate enough wild yeasts to begin working with, but it’d take a bit of time.
In the initial stages of brewing and sourdough starter formation, you’d have an ideal bacteria brewing ground though, and you’d not produce the clean beers & ales that we’re used to today. Your process would get better as you went along, and you could eventually isolate a yeast strain to overcome this initial trouble.
For ongoing brewing, you simply would reserve some of the yeast that drops to the bottom of your fermenting tank, and use that to start your next batch. Modern breweries do that all the time, as do many home-brewers. (usually the reuse a yeast a few times before going back to the “lab strain”) Reuse allows more yeast to be pitched to your pre-beer wort (sugary, malty water), which provides faster starts to fermentation.
The PH of sourdough is not high enough to inhibit bacterial growth, in fact the sour is the result of a lactobasillus (sp?) bacteria. Different areas have different strains of this bacteria, with different flavors.
How would you isolate a single strain? One more thing: suppose you’re tired of creating starters in flour and want to create a primitive form of petri dish. You’re nowhere near the sea, so can’t get access to seaweed to create agar. What other concoction would do? You want it to set and also be filled with nutrients. Would pectin, derived from apples, and augmented with other substances suffice for a primitive replacement?
In the past brewers supplied bakers with yeast. Initial collection could be done by making some beer with wild yeast in the manor of lambic beers just boiling the grain and leaving it in an open container and harvesting the yeast at the bottom of the container when fermentation is complete. You could also crush some fruit and make wine that uses the wild yeasts that will be on the rinds of the fruit.
I once read that every beer brewer in the world 9excpet for the belgian brewers0 use one starin of yeast (saccharomyces carslbergensis), which was isolated at the Carlsberg brewery in Denmark, over 150 years ago. Question: how is this strain kept from muating/eveolving? I’ve made beer at home, and I once tried to use bread yeast-the beer resulting was terrible! What would brewers do if this strain were to die out?
Saccharomyces carslbergensis is a bottom fermenting, lager yeast. Not everyone uses it and ale producers certainly don’t.
Ideally, you keep a small colony of yeast cells in suspended animation and propagate out from that whenever you need a batch-sized colony of yeast. The preserved cells go through a minimum number of divisions and therefore few mutations have a chance to accumulate.
Once you had a yeast population for brewing, you could perform a procedure known as “acid-washing”, which has nothing to do with blue jeans.
Basically it is adding acid and bringing the pH of your yeast slurry to somewhere in the neighborhood of 3.2. Most bacteria cannot survive in an environment that acidic, but yeast will. Unfortunately wild yeasts, including beer-spoilers like Dekkera and Pichia, would also survive this process. But it’s a start.
I don’t know if this would work with bread yeasts, but I imagine that it would.
ralph124c, S. carlsbergensis is the generic name for lager yeast (as Dr. Lao mentioned), it’s actually commonly called S. uvarum now, but there are hundreds of different strains of lager yeast and each subtly affects the flavor of the finished product. S. cerevisae is the generic name for ale yeast, it also has hundreds of different strains.
As part of my job I propagate yeast for 2 large scale breweries and also occasionally provide yeast to a local brewpub, as well as helping out other regional breweries when they develop problems. It is a point of pride to me that I am generally known for propagating clean, healthy yeast , so I could talk yeast all day.
August, thanks for the reply. Could you answer my other question: how would you go about extracting a single strain of wild yeast from a culture with primitive tools? How did brewers hundreds of years ago do it?
And the lambics in Belgium pick up very specific wild yeasts for their (ideally) spontaneous fermentation, Brettanomyces Bruxellensis and Brettanomyces lambicus which are very regionally specific (and the former is considered very bad in wine production).
Mmm. Oude Geuze.
And, our beloved Hefe Weissen is also made using open fermentation, or can be. The brewers swear that this results in a better finished product than closed fermentation. Some breweries “over there” have been in more or less operation for several hundred years.