>Must be a food science term he's hung up on, or something (honestly I
>have never encountered the term

Well that is the difference...a molecular biologist don't consider
food to be an important subject to study but the microbes
itself.....<grin>..

>I was a molecular biologist for 15 years and have had advanced
>coursework in micro, mycology and molecular biology, to name a few. I
>have never heard of "water activity" as being a factor to be considered
>in whether or not an organism will culture on a particular medium.

Really ?
During my microbiology course works..in the university days ,.my first
teacher was a molecular biologist..He talks what we consider an
abstruse..language. to the class that he failed to get us interested
in the subject matter as he delve more in theoretical aspect of cell
structure, metabolism, genetic matter and other deeper aspects of cell
biology... without even relating its importance to practical
application....
One of my classmates asked the instructor....what is the importance of
this theoretical cell biology discussion to food processing...we know
already the basics of cell biology and biochemistry and we are not
graduate students ....that we need to tackle your specialized
discussion head on... ...?

There seems to be a gulf that hampers our absorption of the subject
matter.....Can anybody do the lecture to our own level...? ..The
,majority of the class supported the demand therefore .
..The dean relented as he realized his mistake of assigning a
specialist person...therefore organized for another teacher to handle
our microbiology class. The guy that replaced was a food scientist
..(so much the better. We agreed)..He ( the new teacher incidentally
was actually practicing food microbiologist .....Therefore that
eliminated the' gap'..and enabled the class to realize the
importance of such terms for example the water activity in food
processing

>.) His entire diatribe seems pretty
>simplistic and, franky, dumb, to me, as so many factors need to be
>considered - pH, available sugars, carbs sources, salt concentration,
..light, heat, aeration, etc.

LOL!...silly you....
If you consider this dumb ,,,,,its your own fault as you don't grasp
the concept of water activity from the point in food science ....

As science become more specialized....there are common terminologies
that have different meanings or interpretation from the different
disciplines


Now regarding the other parameters that is also considered....but what
is found in the food formulations is the targeted water activity...the
formulation will indicate what are the available carbs, salt
concentration, and other lesser factors that can affect microbial
growth