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Larry Farrell farrlarr at isu.edu
Thu Jul 5 17:04:07 EST 2001

lamb wrote:

> Do you happen to know why is it that according to the handbooks agar always has to be
> dissolved by boiling before autoclaving?
> We never do, it costs time, it is dangerous, and we want the exposure to heat as
> short as possible. After autoclaving we place the erlenmeyers in a waterbath with
> magnetic stirrers until adding supplements and pouring.
> For larger batches we have nice automatic thingsies, can't think of th English word
> for them.
> Loes

My interpretation of the Difco Manual has always been that the statement, "Heat to
boiling to completely dissolve - - -." referred more to the other media components than
to the agar.  The rationale for that is that the statement appears in the directions for
making various broths as well as agar media.  Given the availability of magnetic mixers,
I always simply mix the medium enough before autoclaving to assure that all soluble
components have dissolved, remove the stir bar and autoclave.  After the medium has
cooled a bit, I simply swirl the flask sufficiently to evenly mix the molten agar.

Larry D. Farrell, Ph.D.
Professor of Microbiology
Idaho State University

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