Melting Petri Dishes?

Howdy all,

I am doing my first petri dish culture from a Chimay bottle. Ive propagated the yeast up to 400ml and now want to get a pure strain by using the petri dish method. I finally was able to make some agar (the first batch was too thick, the second to thin) and poured them into the petri dishes and it solidified well.

I dont have a pressure cooker, and am not planning on buying one for a month or so (if I can get away with it). So far I have used a pot and steamed everything for 15 minutes for sterilization. I put the petri dishes in there, and 2x they have melted. Am I doing something wrong? I am using a big kitchen pot and a metal vegetable steamer to keep it above the water, and just putting the petri dishes on that. Do I need a pressure cooker, and if so, wont these melt in that too?!

Thanks!!
~Brandon

Plastic petri dishes should be autoclaveable or sterile out of the package and disposable. I'd recommend glass...


Pressure cooker will be hotter than steaming.

Hey Brumer, Welcome to the world of yeast culturing. As TXCurtis said go with glass, check out all the usual places like Ebay and craigslist etc etc. As for plating out cultures for purifying boiling will work OK. However you are at risk of long term infections but as you are only doing this to plate them and not to store them you will be OK.

The problem with boiling is this only Sanitizes vs Sterilizes. The difference is spores of mold can survive the boiling process but not the pressure cooking (or canning) process. Also the PH of wort is high enough to allow things that cannot survive in beer to go to town on your yeast growing media/wort. So eventually (a week or more) your plate or slant or what ever will start to grow small hairy things. If you were thinking of preparing some ahead of time and refrigerating them you might find a few unwelcome guests.

I highly recommend buying a pressure cooker it was the best thing (that and a stir plate) for culturing yeast. I can everything and it has already paid for itself. By using a grain bag I collect the hot break and trub from the boil kettle and filter out about 2 quarts of wort from what looks like crud. This I can with my Pressure Cooker and so I have pre-made sterile starters ready to go, in terms of DME saving it only took a couple of brews to pay for itself. When I'm culturing yeast from slants, plates or bottles I pressure cook 1L flask, wort, Aluminium foil and stir bar all in one so I know it is 100% sterile before I inoculate it. I also use it to sterilize anything I can fit in there come brew day as if beats using chemicals.

So the next question you will probably have is once you isolate a colony how do I grow it... check out Maltose Falcon web site on yeast propagation and maintenance. They have really good info on growing yeast. The basic steps are

Plate single colony -> 10ml of sterile wort 48hrs shake often as you can
10ml culture -> 50ml of sterile wort in 250ml flask and stir
50ml culture -> 250ml of sterile wort in 1000ml flask and stir
250ml culture -> 1000ml of sterile wort in 2000ml flask as stir

The 1000ml culture will have around 200Billion Yeast Cells if you use a stir plate. Also to allow you better view of how much yeast you are generating try to only have wort in your flask and decant off the hot/cold break as other wise you end up with 1000ml of trub. At the end you should have about 1/4"-1/2"" of yeast cake on the bottom of your 2000ml flask.

Good luck

Clem

Additional note: your pressure cooker needs to be capable of 15psi and it will reach 250degrees F at that pressure, this for 15minutes is what is required for sterilization.

Thanks guys! I really appreciate the help in this. I will try and go forward with this. I have the stir plate and have used it for starters for the last month or so. I also just started canning wort ahead of time, which so far has expedited things.

Thanks again!!

Was looking for glass petri dishes (ebay has a lot, thanks), and wanted to see the size of the ones I bought. Found this in the description of the ones I bought previously: "May not be used in a pressure cooker." Well, that explains my problem.... dooopppppeeee

plastic are sterile. At least in my lab they are. but once you expose the inside of the dish, they are not.

I culture bacteria, never yeast, but we always have to grow them in ampicilin agar to make sure we are growing the correct stuff. Do you yeast people use anything?

TXCurtis said:

Plastic petri dishes should be autoclaveable or sterile out of the package and disposable. I'd recommend glass...


Pressure cooker will be hotter than steaming.

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https://www.cynmar.com/home.aspx?CategoryCode=133

for petri dishes plus all the other fun yeast ranch equipment

mewithstewpid said:

plastic are sterile. At least in my lab they are. but once you expose the inside of the dish, they are not.

I culture bacteria, never yeast, but we always have to grow them in ampicilin agar to make sure we are growing the correct stuff. Do you yeast people use anything?

Click to expand...

Adding some hops to 10 IBUs or so in the wort does a pretty good job keeping bacteria down, but does nothing for mold. Good culture technique does the rest.

mewithstewpid said:

plastic are sterile. At least in my lab they are. but once you expose the inside of the dish, they are not.

I culture bacteria, never yeast, but we always have to grow them in ampicilin agar to make sure we are growing the correct stuff. Do you yeast people use anything?

Click to expand...

Yeast growth depends on what you're trying to do really. I use Lins Cupric Sulfate medium for detection and or isolation of non-saccharomyces strains. Some sacch strains will show up but you have to know you're strain to not worry. There are also malt extract, yeast extract, peptone, and glucose plates specifically meant for yeast culturing. The pH is adjusted specifically for whether you are growing a brett or a sacch yeast. I go down to 5.0pH for brett and 5.3pH for sacch.

Now as to the dishes. If you can find glass get them. Plastic will do what you want. They're cheap, they should be sterile (irradiated), and they're meant to be tossed. You won't have to melt/scrap agar out of the dishes because you can toss them when you don't want them. As a piece of advice if you go the plastic route they and don't use an entire sleeve, discard at least two if not three when you grab more for use. Discarding a few helps ensure sterility when you go to pour new plates. Also don't stick plastic plates into an autoclave, or pressure cooker because they will melt unless specifically labeled as autoclavable.

smokinghole said:

Some sacch strains will show up but you have to know you're strain to not worry. There are also malt extract, yeast extract, peptone, and glucose plates specifically meant for yeast culturing. The pH is adjusted specifically for whether you are growing a brett or a sacch yeast. I go down to 5.0pH for brett and 5.3pH for sacch.

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I did some googling, but couldnt come up with a whole lot: Do you have any links, or can you do a QUICK writeup about brett and sacch yeasts? Ive seen those names on this board, and have found generic information about each on the 'net, but what are they really and how does that relate to brewing?

Thanks all,


...the wife approved me buying a pressure cooker so tomorrow i get to buy one and try to can some more wort -tonight I noticed the wort I canned last week (via steam) is infected, awesome.

Links to what specifically? I have many resources depending on what you want.