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autoclaving for a second time - (Apr/27/2010 )

Hallo all,

would it be bad to autoclave a broth again?

I have a broth, but I need agar, so I was thinking of putting some agar in the bottle and then autoclaving it again.

Is this ok or?


I was told that it's not wise to do a second autoclaving because the pH of the broth will be affected. But I never tested it myself so I don't know whether it's truth or myth. Just make some fresh media to be safe.


Re-autoclaving burns the sugars found in the yeast extract, which may or may not affect the growth of the bacteria. It is just about as quick to make up a small amount of fresh medium and add agar anyway.


Unless you're critically low on media and don't wish to make new ones, then I think it's fine.

Myself have done that twice (and will make sure it'll never be a routine) and things grow well. They get a lil darker that's all. Grows well for me.

But then, I did that with a broth and I'll spare you the reason why I did that. Not sure about agar though since, like Protein Work puts it, if pH changes, it'll affect the agar after cooling.


depends on the experiment you will need it for; some media will form precipitates or C-sources can be altered when autoclaving for a second time.

If you are working with a standard medium and just want to keep your microbes growing and your microbes do not need some special nutrients its no problem if the medium is autoclaved for a second time. But if you need the medium for an experiment crucial for your research, make a fresh one to be on the save side.