This idea came from a podcast on basicbrewing.com. When creating a yeast starter you need a small quantity of extract, a mini-brew of sorts. Using dry malt extract is expensive and not always available in your home brewery. So the solution is to brew up a small batch of beer without hops for future use. Unfortunately sweet, unfermented wort is vulnerable to infection by bacteria and wild yeasts.
So the solution is to "can" the wort with a pressure cooker. That way you can store it indefinitely and at room temperature, making pitching the yeast for your next starter so easy since you won't have to sterilize the wort by boiling and then cooling it down to room temperature for the yeast.
You make a small batch of beer say, 2 gallons with 3 pounds of 2-row pale malt and then put it in canning jars in a pressure cooker. The process is quick because the pressure cooker only needs to bring the wort up from the boiling temperature of 212°F to 250°F. This will give you about 7 quarts of wort good for about 7 batches of beer!