Old wort for a starter???

I had a little less than a gallon left of wort after sparging to boil volume from last time i brewed. I've had it saved in a sealed jug in the fridge, and it hasn't spoiled yet. The last batch was a belgian blonde. Do you think any of those flavors would transfer over if i made a starter out of it for an oatmeal stout, or an ESB, or should i just go with the tried and true pale DME? If I do use the wort, does anyone have any tips? Boil first or just hot enough to pasteurize? Thanks!

Unless it was pressure canned it's a no-go, unless you want to risk botulism. You've got to either ferment your wort, or raise the temp to above 240F (I think) and can to keep the nasties out.

Stick it in the freezer next time. I make all my starters out of leftover wort from previous brews, haven't used extract in a starter in a long time. Boil it for 5+ minutes before using.

For the future (when you freeze it), a belgian blonde isn't going to transfer any flavors to anything else, because the recipe was probably a pretty simple light ale right? The belgian flavors come from the yeast and not the grains (for the most part).

Definitely boil first, like you were making a starter from DME. I don't see the harm in it, and to me it seems easier to do than just bringing it to a specific temperature.

I have used paper towels to filter out the crap to get that last gallon out of the bottom of my kettle to used for starters, no worries there, but I also freeze it immediately when I do that. I don't know if you have to worry about botulism though. Acid is its enemy (below 4.6), but it also needs an anerobic environment which a jug in the fridge is not so that might keep it safe. To kill it, you need to go to 250 for 3 minutes. Maybe that helps maybe it doesn't, but I don't know enough about the bug to know if you are safe with fridge held wort.