raybark wrote:Just a quick note on agar and gelling.
Once you have the right volume of liquid and have raised it to a proper temperature and given time for total solubility, you're left with a bunch of small molecular clusters. I heard a great description of "octopi with tentacles pointing in all directions". Getting them to gel properly involves growing those octopi tentacles linked together in bigger and bigger clusters, with liquid trapped within.
I speculate that if they cool too rapidly, you get smaller, loosely-bound clusters that makes the whole not appear to gel well, or it let's the liquid separate too easily from that network. That would suggest that a very slow cool is required.
As I type this, it has reminded me of generating color in glass - something I actually DO know something about: it's a similar procedure, involving melting to get every oxide in solution, then a slight cooling to initiate the crystallization of the color-forming nuclei, then a slight reheating to allow them to grow, enhancing the depth of color before allowing it to fully cool.
I think you might be on to something here. Normally I make batches 100ml minimum at a time, as it make the math much easier. When making the tubes, I add the water/agar, cook it for a couple minutes in the microwave, (careful not to overboil the container, as it makes a mess) then add the P793, stir, and distribute to the tubes, which are usually in the wooded block holders so I don't knock them over. The wood probably acts as a insulator and helps slow the cooling. I have not had any issue with these gelling after setting up the initial
process. On that day however, I tried something different, as he flasks were larger, I tried 50ml batches in the individual flasks to save on the distribution step. I had been thinking that my scale which is supposed to be accurate down to .01g wasn't as accurate under 1g, when measuring out the agar. However, the smaller batch size would likely make the heating/cooling much more rapid. When I remade the media in a larger container and the distributed it, it gelled fine. Agar, what an interesting substance.
Ben Belton wrote:NHguy03276 wrote:
the lids have a .45um syringe filter, sealed with silicon for gas exchange.
Not sure what that is.
Now I am very confused by this statement...
At first I thought you might not know what a syringe filter was, But with your Profession is listed as Pharmacist in your profile, and years of labwork, I can't imagine you've never encountered a syringe filter, but I guess it is possible (https://www.amazon.com/Syringe-Filter-P ... 11&sr=1-55). since most molds have spores larger than 1 micron, it doesn't really matter if I use the .22 micron or the .45 micron size.
Then I thought maybe you mean you don't bother with gas exchange, but this would mean yet another major focus of almost every flasker/instructional video/talk/paper is not as important as many harp on... but... I... ...
Which only leaves what I'm actually doing here... which is to drill a hole in the lid just large enough to fit the filter, put some silicone around the hole and push the filter through the hole, sealing the filter to the lid, and adding a cheap .45 micon sized vent to the flask. I'm just noticing that the membrane of the filter on a couple of the older lids is staring to discolor, and I think it means that dust is staring to build up, and hopefully not that the membrane is starting to degrade.