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Questions about agar consistency/quality

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I have some agar I bought at my local food coop and I try to make up some agar "plates" to streak.  I use the term loosely because I have yet to invest in the proper tools.  I am using baby food jars with a small amount of agar in the bottom and a stainless steel cotter pit as my "needle".

The agar I bought is in a flake form.  I tried using the amount recommended by Kai on his wiki page; 3-4 g per 100 ml of wort.  I found the agar was not completely dissolving no matter how long I heated it.  There were always chunks of undissolved agar flake floating.  So, I started adding a few ml at a time of additional wort.  Unfortunately I did not keep record of how much...   ::)

Finally it seemed well mixed so I squirted about 10 ml into the bottom of each jar with a syringe.  It was rather clumpy looking and was cooling and solidifying quickly.  In the end I decided it was not right so I scooped the solid disks out of each jar and put them back in the pan with another approx. 100 ml of wort.  I remelted them and it seemed a bit better, more liquid.  I then refilled the jars.

I have since attempted to streak one jar.  The agar seemed rather solid (stiff) but dragging the "needle" across it made it tear and scraped it along leaving definite scrape marks with valleys and chunks of agar deposited around.  The yeast did grow but it is rather clumpy with the rough agar surface and not easy to find a clean colony.

Was my agar too stiff?  Too soft?  Or is it just that my "needle" is too crude for the job?  I have read that some people use a paper clip for this purpose and my stainless steel cotter pin is the same dimensions as that.

Also, my agar turns out looking cloudier and darker than the pictures I have seen.  I am using a fairly pale wort for mixing it up.  Any suggestions there?

I think your trouble is not having the proper tools for what you're trying to do. I know you're anxious to get started with this, but having the right stuff is essential. Have you ordered an inoculating loop and plates yet? If not, GET ON IT ;)

I think anyone would have trouble streaking plates with a cotter pin and baby food jar.  ;) A paper clip isn't ideal either.

Are there any asian food stored close? Pick up some "telephone brand" agar-agar. Its cheap.

I don’t think it’s the tools. I have used baby food jars and some metal wire before and the agar was smooth. It might be a problem with the agar. Can you pulverize it in a coffee grinder or food processor?

But it is a pain to steak for individual colonies in a baby food jar. That’s why I eventually got Petri dishes.

When I used baby food jars, I just streaked with a loop to get yeast “lawn” and then poured sterile wort from another jar onto the agar to resurrect the yeast.


You really don't think the tools are causing any of his problems? I wasn't saying you can't make it work. For someone with little to no experience with yeast culturing, I'm sure it can turn it into a frustrating task, when it doesn't need to be.

If you are going to use baby food jars, maybe you should tilt the jars as they solidify (kind of like slants) so you have easier access to the agar surface. It would be hard not to gouge the agar when you have to streak perpendicular to the surface.

Tilting the jars sounds like a good idea. But is gauging the agar a problem. I commonly end up scratching the agar on my plates.



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