How do sourdough starters work? Why are bakers talking about it as if it’s alive and would walk on its own?
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Sourdough starter is nothing more than fermenting flour, water, and yeast. The thing is that yeast will just continue to grow and spread as long as it has a food source, and you have given it a LOT of food source. If left in a warm place for too long or too much yeast is added then the bacteria will grow so rapidly that the starter can overflow the container. There is an image out there on the internet of the aftermath of a baker throwing away some starter that had been messed up for a mass batch without thinking and accidentally ruining a commercial dumpster.
Sourdough starters contain live microorganisms such as baker’s yeast and lactic acid bacteria. These microorganisms multiply in the dough and are critical to the making of the bread. Specifically the yeast produces carbon dioxide gas which causes the bread to rise and have small and large holes. While lactic acid bacteria produce lactic acid, which makes sourdough bread taste sour. So yes, the sourdough starter is definitely alive (but wouldn’t walk on its own on account of not having legs).
The sour of sourdough comes from lactobacilli bacteria that ferment sugars into lactic acid. Like most breads that rise, sourdough typically also has yeast in it. A sourdough starter is a stable culture of bacteria and yeast that contains the desired bacteria and yeast for sourdough, living off of flour and water – basically a very wet dough that you keep in a jar to maintain a source of bacteria and yeast. So it is very much alive, it has to be ‘fed’ periodically with new flour so that the bacteria and yeast will maintain a stable population.
A sourdough starter is a colony of yeast that can be harvested to make bread and replenished as more nutritive medium is added and more yeast grow. The byproducts of the yeast feeding off the nutritive medium imparts a particular flavor to the bread. It’s alive the way a beehive is alive.
The main active ingredient in sourdough starter is yeast (and bacteria). When provided with enough carbohydrates (such as flour) and water it will multiply producing carbon dioxide gas and various other processes that happens when dough rises. So the sourdough starter is essentially alive and needs regular feeding and be kept in a suitable environment. You can kill your starter or at least weaken it if you mishandle it. You can also get it infected which changes its properties and therefore the taste and texture of the bread.
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