How to store sugar wort?

The method I’ve yet only heard of, used by breweries and homebrewers alike, is to boil the wort for 10-15 minutes and freeze it. This would also is in line with traditional German Reinheitsgebot.

Personally I use DME for starters.

Best of luck!

Edit: Some yeast labs suggests using a wort of 1.040 to avoid ethanol production when making a starter. Higher gravity may inhibit cell growth.

Keg it.

Put your boiled wort right into a corney while hot. This sanitizes the keg much like heat does in canning.

Store it with your beer in the keezer.

Use a fresh sanitizes picnic tap and line when drawing for use. Attach cO2 at 2 psi just enough to push it. Then remove a fittings.

If done right you don't even need a boil when doing starters. But bringing the wort to a boil for 3-4 minutes and chilling insures sanitation.

I'll do 5 gallon wort brews, or use second running s and bump to 1.040 with extracts

I heard pressure cooking the wort is a great way to make your wort storable for couple of months: https://www.themadfermentationist.com/2014/11/pressure-canning-starter-wort.html

Never tried it myself, due to the lack of a pressure cooker.

One easy and convenient way to store sugary wort in order to make futur starter is to freeze it. You can store your frozen wort in your freezer for a long time (i'd say at least 6 month).

I would advice you to separate your wort into little smaller parts so that you can only unfreeze what's needed when it's needed.