I think I was misunderstood. There were two different approaches
described: porridge "as is" w/o following saccarification where amylase
activity deliberately terminated by heating to 70C (that is
recommended for wheat) and porridge which is saccarified at 62-65C
(recommended for rye bread, the one used for Borodinsky bread).
Saccarification is a kind of fermentation where amylase enzymes convert
starches of malt grain to sugars. In all-grain (professional) brewing
they succeed to achieve 90% and more conversion, in home brewing
75-85%. The readiness (completion) of conversion is checked by iodine
test. Mashing (saccarification) is followed by sparging: rinsing the
sugars from the grain by water. This liquid (called) wort full of
maltose and other sugars is boiled with hopes, cooled and successively
fermented by yeast enzymes (another kind of fermentation). The yeasts
are "baking yeasts": Saccaramices cerevisae, but metabolism is
different from that of dough: because the fermentation is aerobic with
much oxygen the alcohol is released.
There are many very interesting points looking by one glance at SD
baking and (home)brewing.
For example, belgic lambics are SD of beers: they are made by wild
spontaneous fermentation.
Or back to porridges: that is usual matter to add "adjuncts" to the
beer mash, like not malted whole grains of wheat, rye, oat, rice, corn,
to be converted by barley or other malt grain enzymes to maltose and
other fermentable and not fermentable (dextrins) sugars. But amylase
enzymes can't convert starches that are not gelatinized to sugars.
What knowledgeable brewer do? He makes porridge. Or, for several cents
more, he buys pregelatinized oat/rye/corn etc. flakes - see
http://www.listermann.com/Store/products.asp?id=5
that is instant porridge like "Quaker oats".
Dan Wing wrote that old bread is added up to 30% in some recipes for
acidification of dough. Can't say anything about it.