A question on (commercial) yeast in soudough breads made me dig out my notes from a baking seminar from a few years ago, I was extremely fortunate to take a class with Didier Rosada (who at the time was at SFBI and the "coach" of the usa bread team that won the Coupe de Monde.... It was a really cool class!
Anyway, it was fun to look over my notes, and I found a couple of cool items I thought would be interesting to revisit:
1. Sourdough Culture changes: When a starter starts to rise (increase in volume) it means it has switched from reproduction to fermentation. Fermentation is when the gas is being produced (causing the volume increase) and the production of acidity (lactic and acetic). I'm thinking that during feeding there is eating and the production of waster products, but by the time the amount of waste (ie gas) is pushing your volume up--that means the tide has turned and the shift has made to the fermentation (ie flavor developing) stage.
2. Ways to remember the two kinds of acid: Lactic acid is the type in yogurt and sour cream (think--milder), and Acedic is the type in vinegar. Liquid starters encourage lactic (ie milder) and stiffer cultures encourage acedic (tangier) flavors.
3. Schedule of feedings. Rosada really preferred a 3 times a day feeding, but he was definitely approaching this from a professional point of view. Benefits were "perfect culture consistency" and the ability to change quantities as needed for late orders. My notes say that your culture should rise 3 times the initial volume in 8 hours.
I remember we asked him about retarding doughs via refrigeration overnight (as BBA had just come out, and so many books at the time recommended this) and he saw no real reason or benefit for it He said something like "why would you need to slow fermentation down for 8 hours" and I remember thinkging--because you started it late, it's 10 pm and you want to go to bed because you have to work in the morning :-) Definitely a different perspective as a home baker!
The class definitely took a highly technical view of the process, which was very educational. One thing I like about sourdough, though, is even without any of this background info people can make super flavorful loaves with their own process that works for them. I've always been more of a measurer--but I've also always admired folks that just make bread by feel and instinct...