February 10, 2022 - 5:44pm
SD starter yeast vs. LAB
I notice every time I feed my starter there are a lot of bubbles, I wonder if this reponse tell me anything about my SD starter. Attached shows the bubbles after mixing 3 g of starter with 14 g of 85-degree F water. Are the bubbles created by the yeast or LAB? Does this mean there is plenty of strong yeast in my SD starter? Does this tell me anything about the yeast count vs. LAB count? Is this a normal and it does not mean anything? Just wondering out loud here? Thanks.
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I've always assumed the bubbles are caused by CO2 coming out of solution.
But I'm just a computer guy.
Thanks Gary for your feedback.
Those bubbles are created by proteins, Ming.
Just like water soluble proteins in egg whites, if you stir them, they form bubbles and eventually a stable foam (whipped egg whites, souffle) the same happens with wheat proteins.
There are four different proteins in wheat:
Albumin: soluble in water.
Globulin: soluble in salt solution.
Gliadin: soluble in aqueous ethanol.
Glutenin: soluble in dilute acid or alkali.
Gliadin and glutenin together represent about 80% of the total proteins in flour and are present in approximately equal amounts.
When you mix water and pure flour, only one protein is soluble in clean water - albumin. There is very little albumin in flour, so it won't foam much, if stirred.
But with bacteria and yeast added to flour and water as in sd starter, they produce alcohol and acids, so now you have a lot of dissolved proteins inside that little piece of sourdough and it will foam or bubble resembling stirred or whipped egg whites if you stir your starter in water.
Essentially, your bubbles mean that you have a working starter with good yeast and good lactic acid bacteria that do what they do: produce plenty of acid and plenty of alcohol capable of dissolving gliadin and glutenin.
When creating starters from scratch, initially, they do not foam that well when dissolved in water, because there is not much bacteria and almost no yeast, until they grow, mature and establish a proper community of yeasts and good bacteria.
Wow Mariana this is as insightful as it gets, your enlightenment is greatly appreciated. Glad to have a confirmation that my home-grown SD starter is working just fine, I think I just need to feed it more often so it become more active to produce a taller loaf. Thanks.
I was thinking a little further what Gary said above about the CO2. Could some CO2 be in a liquidous stage in that little 3 g SD starter being released as stirred? That 3 g SD starter had been fermented for 24 hours before I scooped it out to feed it so there must be some gas trapped in it.