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A couple of modifications I made to Laura's sourdough recipe came to mind
which might be worth mentioning:  I used milk instead of water, and half
rice and half potato starch instead of only rice flour.

These changes might be important.  Lactobacillus growth is encouraged by
the addition of milk- it will give a cleaner sourdough culture (once upon a
time when I did microbiology, I plated my sourdough and found a clean
co-culture of only yeast and lactobacillus- no other nasties).  And
lactobacillus has amylase activity which helps to break down the starch so
yeast can use it, i.e. grow better.   Potato starch has less amylopectin
relative to amylose than rice flour so is more digestible. Potato has some
soluble starch which is also more easily digestible.   Lactobacillus also
produces lactic acid, part of the "tang" of sourdough.

I also neglected to mention the addition of more liquid with the second
addition of flour and sugar-  definitely wouldn't work without that!

Didn't want you to be disappointed if you tried the directions "as is" and
they didn't work as well as claimed!

Mary T.