Suppose I want to make some wort for yeast starters to freeze for future use. This is my idea for making all-grain starter wort without much extra work.
I'm thinking that rather than making 1.040 wort, I could take the first runnings from a simple relatively low gravity beer, freeze them and then dilute them from say 1.080 to 1.040 with tap water before boiling them. This lets me freezer smaller volumes and take up less freezer space. The sparge water could then be used to brew a beer.
So from 1 gallon of 1.080 wort, I can make 8 one-quart 1.040 starters or 4 half-gallon 1.040 starters. I just freeze in pint or quart containers, then thaw, dilute 1:1 with water, and make a starter as usual.
So, check my math: I make a simple wheat beer from 5# of 2-row and 4# of white wheat. At 80% efficiency, I usually end up with 5.75 gallons of 1.047 wort - 5.5 into the fermenter, 0.25 left in the kettle. Now I want to make, in addition, 1 gallon of 1.080 wort to freeze. That's 80 gravity points in addition to the 270 (47 * 5.75) I usually make, or 350 points total. I want 6.75 gallons of wort (1 gallon to freeze plus 5.75 as usual), so I want to tweak my software for a 6.75 gallons of 1.052 wort. If I change my recipe from 5# barley and 4# wheat to 6.25# barley and 5.25# wheat, I end up with 6.75 gallons of 1.052 wort. Good so far?
Then I just take a gallon of my first runnings, and check the gravity. If it's high (and I think it will be) I do a little math and exchange some of it for some of the remaining wort after all sparging. Then I freeze this gallon in 1 quart or 1 pint containers and I'm good to go.
Does this make sense? Is it reasonable? Do I need to boil this starter wort before I freeze it? Do I need to boil it for a full hour prior to pitching my starter yeast?
I know DME works fine, but the idea of not using any extract appeals, and there is a little cost savings (about $2.50 for a half gallon starter with DME vs 65¢ with this method).