How long can i keep "starter wort"?

I am starting a frozen yeast bank to save $. I will be freezing 10 ml of slurry, and according to my calculations, will need to do 3 starter steps to reach the requisite cell count for a typical batch (not using a stir plate). So I would like to further save $ on the cost of DME, and just make a bunch of "starter wort", perhaps from the 2nd runnings of the barley wine I'm about to brew. Just wondering if anyone has done this, if it will keep for any amount of time, and if is a good idea or not. Thanks!

you can definately do that, I sometimes do and save it in a 2L pop bottle and freeze it. It should last quite some time if it stays frozen. I do boil it again after thawing it out, before pitching yeast.

just allow enough room in the bottle for expansion as it freezes, I have split the bottles before by filling them too full.

Short answer no with the exception of pressure canning. I use a pressure canner at 15psi for 15 minutes and this has worked great for me.

I'm going to disagree with Brad, there is no reason you could'nt collect wort, freeze and then boil when ready to use. I'm no lab guy, but how would that be any different from making beer in the first place, besides the freezing step? We collect wort, boil, cool and pitch yeast. We then have beer. Doesn't really matter if it was frozen before it was boiled, as long as it stays frozen and does get boiled before yeast is introduced.

Freezing...don't know why I didn't think of that. Thanks!

I will also disagree with myself if you plan on freezing. That would also be perfectly acceptable.

I just thawed two quarts of starter wort today, from my last brewday. I brought it up to a boil, cooled it, and then added it to my flask with my yeast.

I briefly boiled it before freezing, but I knew the gravity was only about 1.025 so I wanted to boil it again anyway to get to about 1.040 with the boiloff.

Canning 7 gallons of starter wort is boring as hell, but I have way more shelf space than freezer space.
It sure is nice to just be able to grab a jar or two or starter wort and throw them in the flask.
7 gallons of starter wort lasts pretty much all year for me, with about a days worth or mashing and canning.