30g of agar powder will last a good while but, once you do use that up, if you have a local Asian food store, you can usually get 25g of agar powder for about a buck twenty-five.
What proportions of gelatin and DME do you use? I assume you mix and then autoclave or put them in a pressure cooker? I need to try this. I have been kicking around the idea of culturing for a couple of years now. This forum is getting me motivated to do so many things!
This is the ratio that works best for me (4% that is). I find it easier to squirt 5ml of wort into as many of the 12ml vials as I want slants. I then weigh out enough agar to come out to about 4g for every 100ml. Divide it up by eye into equal portions (and hope nobody walks in while I’m pushing white powder around with a razor blade) and dump a portion into each vial. Shake it up good and then pressure can them.
If I mix in the agar first, it starts to set before I get all the mixture measured into the vials and if I use less than the 4% ratio, my slants “slump”.
Any advices about streaking yeast on petri dishes?
Some people suggest to:
Sterilize inoculation loop,
Get yeast sample,
Streak the whole plate,
Sterilize inoculation loop.
and some people suggest:
Sterilize inoculation loop,
Get yeast sample,
Streak 1/3 of plate,
Sterilize inoculation loop,
get another yeast sample,
Streak 1/3 of plate,
Sterilize inoculation loop,
Streak 1/3 of plate,
Sterilize inoculation loop.
Where would I use inoculation loop and where would I use inoculation needle?
give different approaches a try. Nowadays I simply keep streaking many lines next to each other. At some point the spead of cells gets so sparse that you get nice single colonies. Re-sterilizing the needle between streaks or repeated dillution in drops of sterile water sounds cool but is way to much work for me. In addition to that it increases the time the plate is exposed to the air which is something I try to minimize.
needles are for stab cultures and streaking plates. loops are for picking colonies, scraping lawn and inoculating slants. At least that’s what I use them for.
Here’s something that is related to the culturing topic-harvesting yeast
I have begun serious yeast ranching after rinsing and after washing a yeast cake realized that when I tilted the carboy I would be pouring through the crud that had built up on the carboy walls and neck so I came up with a clean transfer system which MAY work for top cropping
I have a 8" segment of SS tube from a cut off dip tube which I immerse in a bottle of boiling water and let it sit there loosely covered with AL foil until the bottle cools.I attach one end to a hose (PURGED with hot water) which then goes to one of 2 tubes in a #12 stopper plugging a sterilized mason jar.The other tube is connected to a hose ending in a harbor freight hand pump-about 6 bux.when HF pump pulls on the system the vacuum created draws and the clean SS tube picks up the goods in a relatively clean fashion and delivers to the Mason jar(s).
If someone tries this for top cropping please report back
If you are looking for purity, use the second method. This is streaking for isolation. Streak your first 1/3, sterilize (and cool) your loop. Then make a couple passes back into the first third and into the second 1/3. sterilize and repeat.
Alternatively, you can streak quadrants, sterilizing between the third and fourth quadrant.
Or…you can make one pass right down the center of the plate and then zig-zag perpendicular to your first pass all the way down the plate.
Lots of options.
If you just want lots of growth, the first method is a way to do it. You could even make a suspension and do a spread plate.
BTW, disposable plastic loops are awesome! I didn’t think I would like them when I started this job (after exclusively using ni-chrome loops), but I prefer them now. Umm…I just checked the price on them, and it may not be very practical for home culturing…scratch that idea.
I found that even w/o sterilizing between streaking sections I can get good colony isolation. But then again, I never had formal microbiology training.
I got my stuff today.
I will be making plates and slants tomorrow.
I was surprised how small were the petri plates and vials.
I guess I will have to get used to it.
I don’t know if you plan on it, but I would suggest leaving the plates at room temperature for about a week to serve as a sterility check. Sorry, that was kind of unrelated to you question, but its a step I like to take.
I do that too and used to have a fairly high fail rate if I opened the plates before taping them shut. That act of opening them up used to be for flicking off condensation. Now I don’t worry about it the moisture and rarely get spurious growth on any of them.
