Alternative to Autoclave??

Enigl enigl at
Mon Nov 24 11:46:22 EST 1997

In article <65artn$kdj$1 at>, max at writes:

>> Is there an acceptable alternative to autoclaving.... i.e. 60 minutes
>> in a hot oven??  Will treatment in an oven be effective in sterilizing
>> slant tubes that would house yeast cultures in a refrigerator for 6
>> months?  A year?.

You could buy a cheap household pressure cooker for $20-$40.  After all,  that
is all autoclaving really is, in principle.  Or, you can do what John Tyndall
did before autoclaves were invented: Tyndallization. . .   boil the slants
(with medium already inside) for 1-3 minutes, let cool, store (incubate) at
room temperature (20-25C, up to 37C), then repeat for three consecutive days. 
This process lets the resistant bacteria germinate into a stage of growth where
simple boiling will be effective.  You can't use acidified agar (PDA) if you
use this method because boiling hydrolysis the agar into watery mush.  You can
neutralize the PDA agar to pH 6.5-7.0, that helps.

I don't like storing yeasts on refrigerated slants unless they are overlayed
with sterile mineral oil to protect from dehydration.  Even then, they start
losing viability after only 30 days or so.  


Davin C. Enigl,  Microbiology Consultant,
MEAS-Master of Environmental Arts and Sciences.

1.  Discovered heat resistance in mold: _Talaromyces trachyspermus_ (Published
w/USDA) [I used PDA neutralized to 7.0 pH for this project].

2.  Co-author (with Kent M. Sorrells), Water Activity and Self-Preserving
In:  _Preservative-Free and Self-Preserving Cosmetics and Drugs_, Kabara and
Orth, editors.  Copyright 1997,
Marcel-Dekker, ISBN 0-8247-9366-8, Telephone: 1-800-228-1160

3.  Water System Design and Validation for FDA regulations

4.  Preservative Formulation and Stability Testing

5.  FDA Validation Protocols: aseptic, sterilization, laboratory methods

6.  Hazard Analysis and Critical Control Points (HACCP)

7.  Current Good Manufacturing Practices (cGMP)  Audits

Web Site:

November 24, 1997
8:35 am PACIFIC

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