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Agar medium preparation

Postby Dragon2014 » Sun Mar 30, 2014 5:18 pm

Hi Expert,

I bought the nutrient medium agar, but in the instructions it says that I need to heat it in a pot with water and when it is a liquid I can pour it into my petri dishes. I faced the following problems:

1: The nutrient medium was melted but as soon as I went to pour it in the petri dish I was just able to get a little poured in. It quickly got semi-harder the next time and wasn't easy to be poured. Please help if I'm missing something in the process.

2: I have some bubbles of air in my petri dish. I was wondering if there is a way to not get those air bubbles?

Thanks for your help

Former Expert
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Re: Agar medium preparation

Postby connief » Sun Mar 30, 2014 5:36 pm

Hello there,

I noticed that you made a post earlier about the ice cream project. if this question is in relation to that project, you should post that under your first thread so that all the questions in regards to your project can be kept under the same thread. That will make it easier for the experts to answer your questions because they know the context of your experiment. Here are some good Science Buddies links about pouring agar.

http://www.sciencebuddies.org/science-f ... Agar.shtml
http://www.cdn.sciencebuddies.org/Files ... plates.pdf

1. Did you let your medium cool for too long before you poured it? Because if you leave agar out for too long and it starts to cool, it will start to solidify and will make it difficult to pour. Alternatively, you might have not heated it to a high enough temperature--hence why the agar is solidifying so quickly even after you just poured one plate.

2. In the lab, we usually get rid of bubbles with a flame, but if you're doing it in your own home, I would probably advise against that for safety purposes. Like one of the links said, you should pour your agar when it's about 50 degrees C--that should decrease the number of bubbles. Also, just pour the agar slowly and carefully. Sometimes, when you shake the bottle too make, bubbles will form. You can try to use a toothpick to pop the bubbles, or at least move them off to the side. It is good to get rid of the bubbles though because some bubbles could end up looking like a bacterial colony, and it may be hard for you to tell whether it was actually a bubble or colony.

Let us know if you need more help.


Posts: 6
Joined: Mon Mar 17, 2014 1:13 pm
Occupation: student fifth grade

Re: Agar medium preparation

Postby Dragon2014 » Sun Mar 30, 2014 5:53 pm

Thanks for the quick reply,

Yeah it's me with the ice cream question, sorry it's my first time using the forum

Yes, I believe I did 2 mistakes, first I left it to cool for about 10 min, after that I heated again at lower flame. second I was slowly shaking the nutrient bottle while heating it.

Thanks I will take the advise in consideration for my second trial

Thanks that is helpful


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