The Fresh Loaf

A Community of Amateur Bakers and Artisan Bread Enthusiasts.

Micro organisms - air vs grain

marieJ's picture
marieJ

Micro organisms - air vs grain

I've always been intrigued by the biological aspect of sourdough.  There has been much debate about the validity of theories on whether the yeast and bacteria species exist on the grain or are drawn from the air around us via the provision of favourable food sources ie flour & water, etc.

Not being a micro biologist and yet having to find the perfect factual scientific paper of evidence to support either of the theories that abound, I'm yet to form a solid conclusion.  I have wondered though whether I've been too simplistic in thinking that it should be one or the other or even the same yeast & bacteria speciies that exist in the air as on the grain.  Is it possible that there are species that exist in the air that may be different to those that live on the grain, but still enter and contribute to our cultures during the process of sourdough activiation?  There has been much valuable discussion on this site about this topic.  I'd just like to revisit it and hear folk's thoughts on the matter.  I had assumed that the culture of organisms that are said to exist in the air would be the same species that exist on the grain.  Is it possible those found in the air could be diferent species, or different subspecies?  That they all come together to make up our treasured starters?

Also, at the market the other day I noticed packets of flour from Italy for sale (I live in Australia). 

If I used this to create a starter, would the new starter therefore be a culture that is a body of yeast and bacteria strains specific to the Italian locale of origin of the grain that the flour was milled from?

 

Just a thought.

 

Cheers!  marieJ

 

pattycakes's picture
pattycakes

I am in Italy, and although I considered bringing some sourdough along on our house exchange, I didn't. I have made some here with gaarp's tutorial as a guide. The flour and water made bubbles in the first 24 hours. Today I baked my first Italian sourdough, and it is lovely. The bread is a little more sour than the one I have at home, which is not sour at all. It worked beautifully, to my surprise and delight. I started with a stone ground flour called integrale 00. The mixture has had very little exposure to the air, since I mix it up quickly and cover it with plastic.

 

Good luck!

Patricia

LoganK's picture
LoganK

that most wild yeast in sourdough cultures were environmental (airborne).  I've read about people taking San Francisco cultures to the east coast, for example, and even feeding them with the same supplies they took on a completely different set of microbes in a fairly short time.  Maybe this could be tested experimentally.  You could sterilize some rye flour by dry baking at a low temperature (high enough to kill yeast), and then blend it with sterilized water.  Feed with sterilized flour and water as normal to start a new culture and see what happens.  If you get fermentation, it must be from airborne microbes.  If not, maybe most of them come from the grain.  I can testify from beer making that sterile mixtures (boiled at a roll for over an hour) can be aggressively invaded by wild yeast if not properly quarantined using an airlock.

It's absolutely possible that different species/subspecies of wild yeast are airborne as opposed to associated with grains.  There are loads of different environmental bacteria out there, and I'm sure they have specialized niches just like any other living thing.  Certain types of wine yeasts have co-evolved very closely with specific grape varieties, and only exist associated with the plants and in storage and fermentation areas.  People have done genetic research to show that they have essentially been co-selected and bred right along with grapes for thousands of years, such that now they are so reliant on the grapes' specific conditions that they can no longer compete on their own in natural ecosystems.  I've also heard cider makers talk about specific wild yeast populations in favored orchards, and they actually ferment the juice right out in the open.  Maybe the same kinds of things are going on with some grains?

Cool stuff to think about, thanks for starting this thread, Marie!

Logan

 

marieJ's picture
marieJ

 

Thank you all for your detailed responses.  It's amazing the kinds of paths an interest in sourdough culture takes you!  Remarkably, the high cost of sourdough loaves in my city, a slow afternoon where I read a book on Egypt and a general interest in nature, environment and the 'slow food movement', led me to attempt creating my own sourdough culture.  Since then, a whole  labyrinth of laterally related  subject avenues have opened up - begging to be explored!!!

Thanks Logan.  It is cool stuff to think about! Re your comments on symbiotic relationships between yeast and it's host/s I was watching a program last night on Hugh Fearnley's "River Cottage".  Hugh is a foodie (come TV chef foodie)  He has a small cottage and land holding in Dorset, England where he produces and cooks his own produce.  I don't agree with every thing he does but the reason I'm referring to him here is because on last night's show he made elderflower champagne.  He collected elderflowers from a nearby hedge row and demonstrated how the elderflowers carry their own yeast strains.  He successfully created the champagne from water, sugar lemon juice, lemon zest and white vinegar in two black plastic rubbish bins (new bins of course).  Yet another example of beneficial microbiology identified, acknowledged and successfully utilized in an interesting and delicious way.

It will be apple season here in a few months and I hope to drive out to the orchards in the Adelaide Hills to purchase organic apples to try my hand at cider this year, and a sourdough created from fermenting organic apples as the starter.  I can't wait!

Thanks again to everyone for their replies.  With more time I'd love to discuss this further with you. 

 

Cheers & regards

Marie

(off to search the local nursery for elder bushes!!!! :-)

 

Postal Grunt's picture
Postal Grunt

I used to homebrew beer myself and was fortunate enough to have never experienced a massive infection. Having read many books on home brewing, about as many as I have on baking bread, most of my readings usually pointed to the possibility of a bacterial infection if the equipment used in handling the beer wasn't properly sterilized. The most common bacteria cited as a potential danger was the lactobacilli, the same as the desirable bacteria in sour doughs.

Leftover yeast residue could also be present in equipment but most of the time a large quantity of yeast is used in brewing beer. I have a sachet of Danstar's Nottingham ale yeast that I meant to use in a starter for a bread baking experiment. The package contains 11 grams of ale yeast. Bread yeast packets are usually 4-7 grams. The ale yeast sachet says it's to be used for fermenting 1 to 6 US gallons of wort. When beer yeast is pitched at proper quantities, air born yeast would probably have a difficult time matching cell counts. Anheuser-Busch uses a 25% quantity of yeast slurry in each of its fermenting vessels. Bacterial infections are known to mimic fermentation behavior in the beginning stages of sour dough starters and may have been what you experienced on a larger scale in your fermentation vessel.

Even in open vessel fermentations, such as the English square system and some of the Belgian breweries, massive quantities of yeast are pitched for both consistency in the product and to shorten the time period of exposure to air and any subsequent bacterial or wild air born yests. The Ommegang Brewery- a wonderful place to visit- in Cooperstown, NY brews Belgian style ales in open vessels but their fermentation rooms are sealed and the air is filtered. Other Belgian breweries are wide open and not hospital or food producing clean. Their product is less consistent and usually an ale that has a flavor that is considered an acquired taste.

Since you've homebrewed beer, you may enjoy this little factoid. When the Guiness Brewery first studied the yeast strains present in their brewing process, they found twelve different strains. They narrowed their yeast down to one strain and maintained the flavor. Be sure to raise a toast to Sir Arthur the next time you visit your favorite watering hole.

dmsnyder's picture
dmsnyder

Ed Wood, who sells distinct sourdough cultures from various parts of the world, insists that a culture will maintain its unique combination of yeast and lactobacillus species and, thus, its unique growth characteristics and flavor forever. My experience has been otherwise. I've bought his San Francisco Sourdough culture on two occasions. Both times, after a couple weeks of feeding, they produced bread with the characteristic San Francisco sourdough flavor, but after six months or so the flavor changed. The eventual culture was in no way "bad," it was just different. I assume the original organisms were replaced by others, and, from what I've read, the new ones derived from the flour with which I was feeding my culture.

My understanding is that the yeast and bacteria which inhabit grains are mostly on the outer surface, that is the bran. I have fed my starters with a mixture of white flour, whole wheat and whole rye for some time. Also, I keep my starters at about 75% hydration. Dr. Wood does not address what kind of flour one should use for feeding starters, but he does recommend keeping the San Francisco culture as a liquid. I believe this favors the homofermentive (lactic acid producing) bacteria over the heterofermentive (lactic and acidic acid producing) bacteria which prefer a less liquid (and cooler) environment.

With these considerations in mind, I have purchased Dr. Wood's San Francisco Sourdough starter a third time. I am planning on feeding it only white flour. I am splitting the fully activated culture into two portions and keeping one liquid and the other firm. I will still use whole grains in final levain builds, but I will not feed them to my "stock" cultures.

Stay tuned.

David

marieJ's picture
marieJ

Hi David.

Thanks for your response.  I'm very interested to see what results you observe in the two portions of S F starter.

What I love about sourdough is that it is a living breathing, everchanging, fluid organism.  It certainly keeps us all interested!  A warm, nurturing, earthy, productive, health giving, considered, and cognitively stimulating interest.  ......or is that just me ;-)

Cheers Marie

marieJ's picture
marieJ

Hi David.

I've just become even more interested in the future results of your starter hydration experiment.  This last weekend I fed my starter the last of the stoneground whlolmeal flour but had incorporated more spring water than usual.  At a glance it was very wet, bordering on 'runny'.  Since then it has been stored in the fridge in this state.  2 days ago I took her out to refresh  before building a new loaf and she has become unnervingly quiet.  My starter has been fed twice now and kept at room temp ( v.warm spring weather) and all is very slow and quiet and not at all her normal self.  At this stage I hope the culture is just out of balance & will return to normal.  Here's hoping.  I'd love to judge my experience against your experience with a 'wet' starter.

 

Cheers

Marie.

Yumarama's picture
Yumarama

One might wonder how he maintains his stock starters so that they are "San Fran" or "Italian" and so forth. No one (that I've run across, anyway) has reported that their starter from him are "all the same" which they could well be if the starters don't stay true. Does he have giant bins of San Fran flour and water that he feeds his sourdough? However he's keeping them true to the original, surely that method can be duplicated by others when they get that starter at home.

Unless he orders shipments of dried starter from people in San Fran, Italy, etc., on a regular basis.

dmsnyder's picture
dmsnyder

Unfortunately, I don't know the answer. It might be worth asking him.

Dr. Wood advises against freezing his cultures, so I assume he doesn't do so. He sells his cultures dried and mixed with flour in a powdered form. Did he make a lifetime supply from the original culture?

He is so confident that his cultures will maintain their integrity he doesn't even have any specific warnings about avoiding contamination, other that never adding commercial yeast and not heating the cultures above the temperature at which the yeast will be killed.

David

marieJ's picture
marieJ

Terrific discussion.  I have a quick question (currently multi-tasking) ......If yeast & bacteria species essential to sourdough culture creatin exist on the grain - as we know they do - then would it not be more convenient to purchase wholemeal flours from different countries with which to establish  'foreign' starters (that is starters foreign to our own specific locales), instead of importing activated cultures?  I imagine customs may have a say in this matter.  just wondering...

dmsnyder's picture
dmsnyder

Hi, Marie.

Well, it's not as simple as all wheat grown in a particular country harboring the same bugs, at least as far as I know. 

There's a little bit of science and a lot of extrapolation in this whole matter, in my view.

David

marieJ's picture
marieJ

creatin = 'creation'    Sorry

Darth Lefty's picture
Darth Lefty

My SF sourdough culture, made from a Goldrush packet, is quite large and snotty (3c flour 3c water).  I'm busy converting this over to weight measure but never mind, you get the idea, it's like 155% wet.  The directions specify using 1c of it at a time.  So the bulk of the culture remains in the bottle.  When food is added, any microbes in the fresh flour is at a disadvantage, because it will be outnumbered and in hibernation while the culture is awake and swimming and hungry.

I don't doubt there are bacteria at least in the flour.  Bacteria in crushed malt is what allows the creation of lambic beer and I could see how it could be the same way in flour.  The point of a starter culture is to inoculate the food with so much of the strain you want that it crowds out any natural microbes.

dmsnyder's picture
dmsnyder

David

davidg618's picture
davidg618

...to voice any opinion on this subject. However, I have one, its complicated, because this is a very complicated issue; and its not chiseled in stone. It will change as I learn more, and experience more.

The internet is full of information about sourdough starters. SF sourdough has been studied ad nauseum. Here's a bibliography of some, maybe a third, of the sources I've read and tried to understand re sourdough. Be forewarned: most of them are not an easy read.

And, I'm still looking.

Bibliography: Sourdough

http://en.wikipedia.org/wiki/Sourdough

http://aem.asm.org/cgi/reprint/64/7/2616

http://www.nyx.net/~dgreenw/whatisthemicrobiologyofsan.html

http://books.google.com/books?id=eZjIfud742wC&printsec=frontcover&source=gbs_navlinks_s#v=onepage&q=&f=false

http://books.google.com/books?id=Ac4D3_GHByEC&pg=PT599&dq=amylase+present+in+sourdough&ei=TpagSqS6NojszASgoOHZDg#v=onepage&q=amylase%20present%20in%20...

http://books.google.com/books?id=f3Ua43ujjUoC&pg=PA494&dq=amylase+present+in+sourdough&ei=TpagSqS6NojszASgoOHZDg#v=onepage&q=&f=false

http://books.google.com/books?id=VA6y1EMnkpYC&pg=PA227&dq=sourdough+microbiology&ei=3JqgSs-EC6q6ywSFn_HwDg#v=onepage&q=sourdough%20microbiology&f=false

http://books.google.com/books?id=QI0LwWftNDgC&pg=PA4&lpg=PA4&dq=sourdough+Sugihara+1970&source=bl&ots=CI9tlPBZyh&sig=plNy8BI7Dy2ctU-q7a_evVbSeqY&hl=en...

(This one is concerned with the chemistry and utilization of wheat}

http://books.google.com/books?id=2ulokhVcdRsC&pg=PA33&lpg=PA33&dq=amylase+present+in+wheat&source=bl&ots=ZzdcKEyjKs&sig=_g-MxuCVrYpITFMACtNTLGvjbOc&hl...

ehanner's picture
ehanner

Over the course of time, humans have learned to use the biology that exists around us in a beneficial way. For most of history and one could argue that even today we are mostly ignorant of the life forms that surround us and affect our lives in some way. Naturally fermented foods have been found to last longer and digest better in the human body. From kimchi to sourdough to dandelion wine our food supply is bustling with biology.

I would think there are hundreds of variations in the populations of natural levains around the world. This makes sense if you consider the variables of different flours, harvesting methods and the feeding and storage conditions of each baker, and other things that might have been present at the time the culture was originated like a fruit. As Debra Wink has written here, the storage and feeding conditions will materially affect the population of the culture. If you provide an environment that favors one bacteria over another, that one will thrive and the other/s will lie dormant or die off.

When we mix a dough and inoculate it with a culture, a population of bacteria and yeasts, the possible variations in flavor outcome are considerable. The make up of the dough, hydration, dough temperature and fermenting time will all affect the final outcome. Change any one of those things and the result will be a change in the flavor of the bread.

I have come to believe that the storage temperature and feeding schedule of the starter have a greater impact on bread flavor and rising power than any other variables in my control. Ferment time of the dough and temperature have more to do with sour.

I have bought and started Woods cultures, the Goldrush culture, several dried starters sent from friends in Europe and dozen or so of my own concoctions and baked great bread from all of them. I honestly can't say that I have found much difference from one to the other after they are active and stable and reliably doubling in less than 12 hours. I wasn't able to make a good sour SF Wharf bread until I changed my storage habits and started leaving the starter on the counter.

Eric

SallyBR's picture
SallyBR

I am a microbiologist/biochemist/molecular biologist, but do not have professional experience with food microbiology. 

What I can say about it will reflect a more general view on how microbiological populations behave.

Let's say that you bought a sourdough culture - it will have a specific combination of yeast and bacteria and it will be present as a pretty big initial inoculum when you mix it with flour and water.   So, initially your sourdough culture will be almost exactly the same as the "source".     As time goes by and you keep refreshing your starter, it will change because other organisms will "contaminate" it.  Not in a bad way, at least not necessarily.  These might come from the flour you use, or from the air - keep in mind that tropical places have a much higher density of microrganisms in the air than colder ones).

There is nothing wrong with freezing a starter - if you raised your own and want to make sure to have it more or less unaltered for a long period of time, save some of it and freeze it.   If in a couple of years your starter begins to fail, or gets contaminated by a nasty bacteria (some might make your starter turn a little red) - just go back to the frozen starter and revive it.

For a starter to be completely changed, though  - it would have to be contaminated by a strain of yeast or bacteria with huge advantage for growth in the sourdough mix, so that it would become the predominant species, inhibiting the initial ones. It does happen, but not very often.

 

 

Mini Oven's picture
Mini Oven

before freezing.  I try to create am extreme condition so that the beasties go comatose or produce spores so that their species survive the extreme conditions better.  A live plump cell is more apt to pop when frozen thus killing it.  If the starter is full of plump cells and few spores when frozen it is more apt to be invaded upon awakening than a starter that is "prepared," or has many spores within it.   It will awaken stronger and can defend itself.

I think when most starters "go to sleep" on their own, it is due to some circumstance that has triggered sporing.  Maybe the whole starter is not affected, maybe only a few cells, but they have communicated to other cells thru a chemical substance that they will produce a spore.  This in turn has a domino effect and soon the whole starter appears lifeless while it has gone into a state of survival putting all its energy into producing spores instead of replication.  When conditions are "right" the spores will return to their lively state where we prefer to have them consuming reproducing and producing gas to raise our bread. 

Conditions that produce sporing should be avoided unless you wish to put your starter asleep.  That's why care of starters is so important.  Drying, drastically reducing water in the starter is one I can think of, depriving it of food is another, maybe even too much water,  lowering pH, raising pH, intoduction of antibiotic or antifungal material  could also start a chain reaction.  Extreme heat, cold or temperature, alcohol, to name a few more.  I'm sure there is a longer list somewhere, they might even be affected by light and darkness, air pressure, herbs and spices, spring and fall, frost as well.  Maybe even substances in the water trigger a reaction.   Most of the time starters are pretty resilient and probably go thru cycles of sporing and bursting to life all the time but we never ever notice it.    After all they sure are tiny.  Only when they get their timing together and act as a group do they seem to have power over us, leaving us elated when we've successfully started a starter or feeling lost and confused when they don't produce gas.

So where am I going with this?  I think many times when we think we have "killed" a starter, it has only gone to "sleep" and the chances of reviving it are pretty good.  We just have to establish the proper balance in the starter so the spores can "wake up."   That is, provided the starter hasn't been invaded by an antibiotic or anti fungal growth.

It all comes down to how the yeasts behave in nature.  They are on the ground and on the grain.  They adapt to weather conditions and they survive from one year to the next through their different cycles of reproducing themselves.   Some spores are in the air but not nearly in the same numbers that are spread throught nature on plant surfaces and in the ground.  There is more nurishment there as opposed to the clouds.

Mini

 

 

pattycakes's picture
pattycakes

Mini, that is the greatest essay on starters I' ve ever read. It is so true! When my new starter looked healthy, I was so happy. It went to sleep, and I was depressed and confused. Now I'm happy again because I see the dough full of life, the starter bubbling away; it's life affirming! I said to my husband, "Listen to this! I'm not a nut job...this describes it perfectly."

So thank you. It was a delight to read your treatise on starters.

Patricia

marieJ's picture
marieJ

Marvellous information Mini, and Sally! 

This is the information I have been craving.  I've often thought about the life cycle of our sourdough orgaisms as they would exist in nature and the different stages of their life cycles.  I've clearly had an accurate notion of what happens, but the information generously given here provides all the accurate specifics!  Beautiful, succinct scientific information.  With this and everyone's sharing of observations and experiences I can't help but think we are all now armed with a great formula for success and successful well informed experimentation.

Mini your notes on conditions that encourage cells to enter dormancy and produce spores was very interesting.  I have recently thrown out my beautitul starter due to carelessness via her last refreshment.  I always have kept my starters at the consistency of a sticky unworkable dough. However, the last refreshment I gave my 'late' starter was highly hydrated - almost to point where I could have poured it out of the bowl, but not quite soupy.  I thought it would exist happily like this for 5 days until I could get to the shops to buy more flour.  When I fed it again it was unnervingly quiet.  I now understand it may have entered a state which you have described, as a response extreme conditions.

I decided to persevere and continue to feed her in a rescue attempt.

Activity resumed on day 2 of twice daily feeding. 

Why did I discard this starter?  The reason was that I felt the balance was between organisms was out.  The gas being produced was harsh.  The lovely sweet apple cider aroma had been replaced by a harsh smell that was like razor blades up the nostril that was unfortunately closest to the bowl!! 

I was initially prepared to continue to feed the starter to see whether the balance would correct itself.  Especially as the centre of the starter still had a lovely deep red wine aroma.  It was the surface gas that was severe.  However, I could not be sure if the harsh gas was being created by an intruder organism, or if it was just the fact that maybe only 1 or 2 of the sourdough species was producing gas at that point in time, ie the first to reactivate after the extreme conditions, (?) ie just the lactic bacteria and not the yeast...??  It was the not knowing that led to her demise.  Also, I decided to use the fresh flour to begin a new starter instead of the potential waste on a starter that my have been doomed.

Is it ever worth pursuing an inbalanced starter?  Given that most of us are novices?

Can we ever be sure of the microbial species that exist in our starters and assume they are not harmful?  My discarded starter had all the visual attributes of a fresh healthy culture.  It had not discoloured.  It was just that razor blade gas and the uncertainty of the facts that showed her the door to the compost bin.

Marie

 

 

Mini Oven's picture
Mini Oven

Glad you came over to this thread.  I was going to suggest it.  Great minds...  I did comment on the other thread.

The deep wine aroma was telling you to feed it.  You might have taken just the inside part, fed it and watched what would happen.  Important is the feeding.  There is a lot going on in the starter and discard/feeding does seem to balance more things out than what we can plainly see. (Providing the food and water are not the problem.)  Normally thinning a starter makes it consume the food faster.   Keeping them stiff or refrigerating slows them down.  (And everything seems to have limits.)

Oh well, your compost is very happy. :)  Off to a new start!  Full speed ahead!

Mini

marieJ's picture
marieJ

There's a new baby bubbling away in the crib........... 

pattycakes's picture
pattycakes

As part of this thread, please take a look at my post:

http://www.thefreshloaf.com/node/14078/sourdough-went-sleep-and#comment-87007

and tell me if you have any ideas. My starter is slowly waking up, but I am baffled at the falling-asleep part.

Thanks!

Patricia

pattycakes's picture
pattycakes

The starter is now making good bread, and I have an Tuscan starter to take home!

I suppose it begs a name...Luigi, Dante, Santino?

Patricia

 

Postal Grunt's picture
Postal Grunt

How about Marco? When you decide to build up another starter to go along with the Marco, you can call it Polo.