Making agar with pressure cooker - (Oct/03/2007 )
I have problem solidifies my agar.
I have limitation of equipment in my office lab. I am currently using pressure cooker to make agar.
My steps is as follow,
1) Mix 8g of 1.2% working strength agar and 15g of tryptone soya broth with 500ml of water
2) Place the bottle of mixture in a pressure cooker with water and heat up for 15mins
3) Place aside the bottle of mixture aside to allow the pressure to settled down for 10mins
4) Take out the bottle and shake to allow the agar that settled on the bottom of the bottle to mix with the solution
5) Place the bottle of mixture to a water bathe of 55oC to cool down for about 10 mins
6) Take out the bottle of TSA agar and pour into petri dishes
7) The petri dishes is place aside for an hour to solidifies
But after 1 hour, the agar is still soft, did i do any things wrong?
Thank in advance 
do mean still soft or still liquid.
If it is still soft (as in solid but still soft agar), increase the amount of agar you are using. Try 10g agar per 500ml
If the agar is still liquid. (liquid like water), the fault is the pH. Agar will no solidify below pH 4.5. Add some NaOH, and adjust the pH to 7 (if pH 7 is okay for your medium) About 1ml of 1M NaOH per 500ml should do the trick (but measure the pH! 1ml 1M NaOH may not too much or too little)
My agar is more to soft.
Thanks i will try with 10g of agar power the next time round.
I have limitation of equipment in my office lab. I am currently using pressure cooker to make agar.
My steps is as follow,
1) Mix 8g of 1.2% working strength agar and 15g of tryptone soya broth with 500ml of water
2) Place the bottle of mixture in a pressure cooker with water and heat up for 15mins
3) Place aside the bottle of mixture aside to allow the pressure to settled down for 10mins
4) Take out the bottle and shake to allow the agar that settled on the bottom of the bottle to mix with the solution
5) Place the bottle of mixture to a water bathe of 55oC to cool down for about 10 mins
6) Take out the bottle of TSA agar and pour into petri dishes
7) The petri dishes is place aside for an hour to solidifies
But after 1 hour, the agar is still soft, did i do any things wrong?
Thank in advance
1.2% Agar is very less, and no wonder u get soft agars...
* Use atleast 1.5% agar,
* And if u really want some good solid surface for streaking, 1.8% agar will do. This makes the streaking easier (media doesnt tear or plough).
* After adding the ingredients and agar to the water, heat it in a water bath or hot plate or microwave oven to completely melt the agar.
* Now autoclave or use the pressure cooker (doesnt make any difference, infact the latter is quicker).
* After u take out and cool it, mix well to prevent agar settling down. Also mix before u pour every plate.
* And most important is pH.