[Avodah] size of a kezayit

[Zev Sero]

Yitzhak Grossman wrote:
> Zev Sero <zev at sero.name> wrote:
 
>> Now we do seem to have a dispute about the density of matzah, since
>> all the older sources assume it to have approximately the same density
>> as water, and the well-attested minhag in EY was to weigh 9 dirhams of
>> matzah for a kezayit, explicitly on this assumption that it has the
>> same density as water.  If more recent experimental data shows this
>> assumption to have been incorrect, then the weight required must be
>> adjusted accordingly.

> Note that Ralbag (cited by Kessef Mishneh, Temidin U'Mussafin 5:9)
> asserts that the density of Matzah is at most slightly less, and
> probably actually greater, than the density of flour:
> 
> <Quote>
> And it is clear that dough, when it has been made into Matzah, will not
> increase in quantity [volume] over the quantity of the flour, and if it
> will, it will be but little.  But we can see "b'hush" that the quantity
> of this dough is less than the quantity of the flour. 
> </Quote>

Yes, but flour is much less dense than water, and this has long been
recognised in halacha.  For instance, the shiur chalah is an isaron of
flour; taking the Rambam's shiur of a revi'it of water weighing 27
dirhams, and the Ottoman dirham of 3.2 grams, this would be 2.5 litres
of flour, which if it were as dense as water would weigh 2.5 kg.  But
the actual shiur used for chalah is approximately 1.5 kg, because flour
is something like 3/5 to 2/3 the density of water.  (RACN weighed
various kinds of wheat flour and found differences among them, but none
even approached the density of water.)

So the fact that matzah is more dense than the flour from which it
was baked is no surprise; the question is how much more dense.  The
older sources assume that it's only negligibly less dense than water.
The experimental data cited here on Avodah challenge that assumption.

-- 
Zev Sero               Something has gone seriously awry with this Court's
zev at sero.name          interpretation of the Constitution.
                       	                          - Clarence Thomas