Questions about DME in a starter

Hello, I am planning to step up a yeast starter for a lager, but I only own a 2L flask. I can get the 300 billion yeast I need by adding a 2 liter starter to another 2 liter starter. Is it not possible to make a true 2L starter with a 2L flask?
Do I account for the volume of wort added by the addition of the DME, or just add the DME to my flask and then top the water up to the 2L mark? I'm just unsure if I factor to volume of the DME when making a starter or just fill two liters of water in the flask and then just add the DME, hoping there's enough room for 200g of DME and the water in the flask.

I can't really give you the answer to your question, but I guess that's mostly because I'm sort of confused what you're attempting to do here - are you asking about making a starter in general or making adding more starter wort to a fermented out wort?

Assuming you're asking about just making a starter in general - the DME will dissolve into the water and create a starter wort - the DME itself is not going to create a large volume in your flask. If you're really worried about it, just boil up a smaller amount of water + the DME and top up with more boiling water until you reach 2L.

If you're asking about stepping up a starter, you're just adding more wort to the slurry you have from the first starter and you'd have to either get a bigger flask (which you don't have and if you did, you could just make a bigger starter to begin with) or you'd have to decant off the spent wort - in either case you need a separate container to boil and chill the starter wort and you can just add less if the amount is too big for your flask.

Thanks, I thought the wort would contribute quite a bit to the overall volume. I was actually thinking about both since I'm stepping up a starter. I'm considering decanting the first yeast starter in a sterilized mason jar and then adding it to the second starter.

It's tough to go a full 2L in a2L flask because you add the DME to the 2L volume which pushes you over the limits for a 2L flask. If you're not using a stirplate then ANY container can be used for a starter as long as you can sanitize it....go buy a gallon of apple juice in a glass jar and you're set...drink or dump the AJ....or buy 4 and start a batch of apfelwine and you'll have 4 starter vessels of 1 gallon each!!