Per the book’s instructions, I left the jar alone for 3 days to do its thing. The mixture showed significant activity (as indicated by bubbles and rising height) within the first 48 hrs - this is typical of new starters. Despite looking like a very active dough, this initial burst of activity is a mix of a whole bunch of funky bacteria that will be largely replaced by other types as the starter matures. By 72 hrs the starter had begun to acquire a vaguely acetone-like smell, typically an indicator that the stuff living in it is getting very “hungry” and stressed (see below for further explanation). Nonetheless, as instructed, I removed just 20% (50 g) of the mixture, and replaced it with an equal amount of fresh material: 20 g rice flour, 10 g corn flour, and 20 g water.
As I stated on Day 1, I had some doubts about whether I was understanding this part of the recipe correctly. Often recipes for a new starter will instruct to discard 50% or more of the fermenting mixture, and replace it with (at least) as much new material. That's about the ratio I'm used to with my previous successful GF starters too.
Why discard so much flour? To answer this question we need to look closely at what’s happening in a new starter. We begin with flour and water; these provide all the nutrients necessary for whatever kinds of bacteria and fungus are present to grow. At first, we have all kinds of things growing - the kinds we want for bread, which will produce good flavors and make the bread rise, but also plenty of things that make funky smells, molds, and perhaps even some things that (if allowed to grow in sufficient quantities) could make us sick. As these various organisms break down the starches, proteins, and other metabolic processes in order to grow and reproduce, the mixture grows more acidic. The increased acidity is crucial to the process of becoming sourdough - the organisms we don’t want can’t grow very well in the acidic environment, allowing the acid-tolerant bread bacteria and yeasts to thrive with less competition. However, this is far from the only chemical change: you also have other metabolic products of the fermentation process and the old cells that have died.
When these products build up in proportion to the fresh resources in the mixture, the bacteria and yeasts may go into “survival mode” - they start producing molecules that aren’t desirable for bread, and also in turn the altered chemical environment of the mixture negatively affects the diversity of the microbial community. So, when you remove some of the starter, you’re not just removing flour, water, and the stuff living in it - you’re removing dead stuff, undesirable chemicals, and other things that would get in the way of a robust sourdough community. Discarding and feeding the starter both controls this buildup and provides fresh resources at a ratio that allows the desirable organisms to take over.
All that said, I have definitely found plenty of old and traditional examples of fermentation methods that seemingly go against this wisdom yet still produce bread. Some of those are also fairly dry/stiff mixtures like this one is, which may be significant. So, for now, I am continuing to give this recipe (and my translation skills) the benefit of the doubt. Check back in a few days to see the progress!