According to Jewish law, glass is non-porous and
does not absorb or leech anything placed in it,
regardless of the temperature of the product placed
in it or the length of time.
In fact, glass can be interchangeably used for both
meat and milk products, as long as the glass is throughly
washed between uses so as to completely remove the product
from the surface of the glass.
There are customs to allow the glass vessel to be purged
in water changed over a series of three days -- but this is
only a stringency taken upon certain groups of their
own stringency.
Only metal, plastic, and earthenware vessels absorb and leech
products stored within.
Metal can be koshered through certain methods so as
to allow change from meat and/or milk but not plastic and
earthenware since plastic and earthenware (non-glazed)
will never completely adsorb whatever has been stored within.
Contrary to popular opinion, true Jewish law does not ignore
science, and in fact, is extremely cognizant, concerned with,
and follows scientific fact, hence glass's kosher status.
In fact, there is a section of the Babylonian Talmud (Taanis)
that explained the relationship between pig diseases and
human diseases centuries before the current outbreak of swine flu.
The area of Jewish law contraversy lies in the areas of
science which deal with biology and geology, specifically,
with regards to the age of the earth/universe according to
biblical aging versus modern scientific theory.
This is a very long and involved topic, but in short, issues
regarding earth/universe agining as per modern scientific theory
can be reconciled with Jewish biblical beliefs.
A major component of this resolution revolves around the first
six days of creation and the lack of the current laws of nature
being in force during those first six days and the affect the
laws of those six days had on what can be observed and
measured today.
