what do you store them in? Fridge vs freezer
Plates and slants are stored in a refrigerator at 4C/40F.
The plates are for isolating and the slants are for storage, right?
How long do they store before you should redo them?
The process of inoculating a blank slant from a slant that contains a culture is known as "subculturing." The amount of time that a slant will remain viable on a slant is strain dependent. Some strains will last two years without subculturing. Other strains, need to be subcultured every six months.
What do you do if you want to use one?
While many breweries use the master/working slant model. I do not brew enough to use this model, and any amateur brewer brewing with multiple strains will more than likely not use the master/working slant model. One the tenants in my brewery is that one should limit the amount of handling any yeast culture receives. A lot people who purchased yeast on slant form BrewTek did not subculture. They merely used the slants that they purchased for multiple inoculations. I do not recommend that model.
I posted this information earlier in the thread.
The use cycle is as follows
1) Pick the slant that has the most robust growth
2) Subculture two new slants from this slant (i.e., inoculate new blank slants with the loop using aseptic transfer technique)
3) Inoculate 20 to 40mls of autoclaved wort from the slant using aseptic transfer technique (I usually use more than one scrap)
4) Discard the slant that was subcultured and used to make the starter (i.e., the other old slant for this culture can be discarded at this point, or one can wait until the subcultured slants proof before discarding it)
5) Incubate the slants (caps loose to allow for offgassing) and the 20 to 40ml starter
What will happen during incubation is that yeast will cover the surface of the agar solidified medium. I usually let the incubation period run until there is no change in the amount surface area covered by yeast. I then tighten the caps (they have to able to offgas while incubation), wrap a strip of Parafilm (a wax coated plastic wrap) around the cap and the tube, and write the culture number, date subcultured, and the generation from the original culture (the generation here is the slant generation, not the yeast cell generation because multiple generations of cells grow everything a culture is subcultured).
The 20 to 40 milliliters of sterile wort will usually need to be incubated for at least a day before being stepped up in volume. I usually let my first level culture grow for two days because I innoculate 40mls of autoclaved wort. If one is very clean (I mean anal retentive clean), 40mls can be stepped to 1L of boiled starter wort. That's a 25:1 step ratio, so sanitation cannot be be lax (i.e., no "spray and go" Star San sanitation, in fact, no Star San period). I usually step 15:1, but I rarely grow a starter that is larger than 600ml due to my batch size being 3.5 gallons. A safer approach for someone just starting out is to use two steps. The first inoculation is 10mls of autoclaved wort. That culture is stepped to 100mls using autoclaved wort, and finally to 1L of boiled wort. That sequence got to be old fairly quickly, so I started bumping up the volume of the initial inoculation.
When growing a culture from such a small amount of yeast, we have to be mindful of what I am going to start to refer to as time-to-own, which is the time between inoculation and the culture owning the medium. The ratio between the medium volumes affects the time-to-own. The larger the step, the longer it takes the culture to own the wort. Extending time-to-own means that sterilization and sanitation become more critical.