It isn't just flour, water and yeast. In fact, one of the most important components growing in that gruel is the microflora-- a spectrum of lactobacillus bacterium, that gives unique flavor, acidity, increased shelf life, and greater digestibility to your bread. But is there too much of a good thing?
I like to think of yeast on one side of the seesaw, and lactobacillus on the other side. Too much yeast and you won't have as much acidity. Too much acid and the yeast becomes sluggish, producing too little carbon dioxide.
Control the yeast to lactobacillus ratio with proportion of "seed" starter that you dose your starter with in regular feedings, and by controlling temperature and frequency of feeding. Most important, taste and observe your starter fine tuning for the flavor you like. I prefer a mild-lactic quality to my starter. For me, I want it to taste like yogurt, rather than have a sharp acidity.
Next post will be on temperature and consistency of starter. And what happens when you use whole wheat or rye flour. Kay?
Photo credit: Modernist Bread