Okay, clearly there is something wrong here. Yaweh says no
leaven is to be in your house, and that you are not to eat food
with khametz in it. The above Orthodox rules tend to go a little
too far, don't you think? And remember, in the NIV, Exodus 12:19
says: For seven days no yeast is to be found in your houses.
If that were the case, then the NIV has just asked you to perform
the impossible: For instance - stop reading and take a deep breath.
You've each just inhaled millions of yeast spores! Natural, wild
yeast is all around you, including in your homes; you can't avoid
it.
So what, exactly, is yeast? We know that bakers use it to make the
dough "rise"; without it, our bread would be nothing but flat, hard
cakes - like what? - Matzah! Clearly bread has been around for a
long time.
We don't know when or how the first leavened bread occurred; only
that the first records of any sort of bread are in ancient Egyptian
hieroglyphs from around 5,000 years ago which depict bake-houses
with dough rising next to bread ovens.
In ancient Egypt, wine-making and brewing occurred alongside baking
and, it's possible that some fermenting brew - a kind of liquid
yeast known as barm - could have have ended up in the bread dough
which then caused the dough to rise. No one knows how it happened,
but one good guess is that Yaweh simply told man how to make
bread.
Continuing with the topic of yeast, the exact nature of yeast -
where it comes from and what it is - has remained a mystery for
thousands of years. It took, in fact, the invention of the
microscope in the early 17th Century to finally allow scientists to
see what a single-celled yeast looks like and they soon realized
that yeast cells multiply in a sugar solution, but they did not
realize in that era that the cells were actually alive. A 19th
Century food chemist thought it was decomposition of the cells that
caused fermentation, and refused to accept the theory that yeast
was a living organism.
It took Louis Pasteur to solve the mystery in 1859 when he
discovered how yeast works. He established beyond doubt, using
grapes, that it was the dust on the surface of the grape skin which
made wine ferment, that yeast was a living organism and that only
active living cells can cause fermentation.
Simply stated, the fermentation process in dough can be described
as the breakdown of the starches in flour - producing carbon
dioxide - which, in turn, expands the gluten proteins in the flour
and causes the dough to expand. A small amount of alcohol is also
produced, but this burns off as the bread bakes.
