Continuous culture of the sourdough starter vs the stop start approach of a home baker is really the big difference between a home baker and a commercial operation and most home bakers do nothing to compensate.
The continuous approach in a bakery is exemplified by the starter culture being doubled every 6-8 hours 365 days of the year (almost). The home bakers approach is to store the culture and use it intermittently and so it is worth examining what exactly happens during this storage process.
The notion of the yeast sporulating on storage etc. is virtually guaranteed to be wrong for almost all starters. No wild strain of yeast can sporulate as is frequently stated in books on sourdough, the FAQ etc. wild yeast most commonly are aneuploid or polyploid and thus they either do not sporulate or spores have very low viability. Also no spore would germinate in the 8-12 hour proof given to it in a bread making regimen. Both the lactobacilli and yeast are simply dormant in a stored culture and a certain fraction is continuously dying as elaborated below.
Both the yeast and lactobacilli are inhibited by the acid produced. As you store a culture the organisms die - lactobacilli at acid pH die at the rate of 90% a week when stored at room temperature. At cooler temperatures the rate is slower (4 weeks needed at 4 degrees for 90% mortality). Because the starting culture usually has a large number of organisms (in the order of 10E7 - 10E9 (10000000-1000000000) per gram of dough in an active culture with the lactobacilli being higher than the yeast) this very high death rate is not immediately perceived - the culture is progressively enfeebled. At neutral pH the death rate is slower (incidentally this is the logic why you feed and proof your starter for a very short time before you return it to the fridge - the proteins in flour neutralize some of the acid improving survivability and all the nutrients are not depleted so the culture can grown at a slow rate in the fridge).
If you do not use a culture continuously but store a culture in the refrigerator over time only 10%, 1% or less of the culture will be alive depending on how frequently you use it, what the acidity of the culture was when you stored it etc. Simply, feeding the culture with a equal volume of flour water does not bring the number of lactobacilli up to the maximum number possible - a two fold dilution does not really relieve the acid inhibition adequately, and instead of 10000000 organisms/gram you may have only 1000000 or less. The culture is thus never really vibrant - it is simply limping along.
What I do therefore is to do a very large dilution when I pull the starter out of the fridge say 1/2 to 1 tablespoon to 1/2 cup flour and a similar amount of water. This dilution relieves the acid inhibition and allows the culture to actually divide and grow back towards the maximum possible. 12 hours later I refeed (doubling the starter) and repeat this until I have the amount of starter I want built up. I always try and adjust this so that there are at least a few doublings of the starter before I actually incorporate it into a dough. I have used starters from Sourdough International exclusively so cannot comment on the success of this approach with non-traditional starters (i.e. anything that is fed on something other than flour and water). This regimen gives a starter with excellent properties, with respect to souring, leavening etc. This is slightly more work than most people usually do but you will be rewarded by an improvement in flavor, dough characteristics, etc.
-Roland
What is good feeding? I believe that there are two important things:
First, don't starve the culture. This means that you should feed the culture once it shows evidence of strong activity (frothing or rising depending on the thickness of the starter) and not too long after that. If you feed too infrequently the cell populations in the starter will begin to decline due to starvation, etc.
Second, feed the starter by quadrupling (or even quintupling). This means that you feed the starter three times it's weight each time you feed it (i.e., if you have 2 oz of starter, feed it 6 oz of new food). If you don't have a scale you can do the measurements by volume, but I think weight is better. I also think that it is best to keep the starter at a relatively thick consistency. Both the dilution at feeding and the thick consistency are designed to encourage the presence of certain good lactibacilli. FYI, when one feeds by such extreme dilution, it is not necessary to maintain a partiularly large amount. Starting with a tablespoon of old starter and mixing this with a quarter cup each of flour/water at each feeding will leave you with a sufficient amount of starter.
-Sam
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This page was last updated on Tue, Aug 3, 2010 at 7:52:54 PM.