yeast Media

[jamiejlg]

Hi folks! I have a mysterious media making occurrance- hope you can help...
I am making Semi Rich Media (SRM) for yeast.
SRM is :
0.2% Bacto peptone
0.1% yeast extract
0.3% casamino acids
0.17% YNB without amino acids and ammonium sulfate
0.06% KH2PO4
1% glycerol
I adjust the pH to 6 with 2M NaOH and autoclave.

I've made this media 4 times. The first time, I made 1L and everything was fine.
The second time, I made 1L in 2 separate bottlesand both Liters had a precipitate after autoclaving.
The third time I made it, I made 1L in 2 separate bottles again- one liter had ppt and the other did not.
I pH'd the third batch and the liter with the ppt dropped to 5.4. The other without the ppt was 5.8.

Can anyone help me? Is it temperature fluctuations in my autoclave? Is it evaporation? anyone's suggestions would be very much appreciated- there must be a sensitive component I'm not considering.

Thanks-
Jamie

[MichaelXY]

NaOH may react with air just sitting in the jar, and produce NaCO3. Could CO3 react with any of your media?

[jamiejlg]

Hi- thanks for your reply...I never did find out what was the cause of the precipitation. I just opted to sterile filter the media instead and save myself the grief! Thanks and happy holiday!!