I view parti-gyle wort a lot like leftovers, it may not be ideal, but it can be delicious when prepared correctly (not to mention it's free). Unless the big beer is high gravity there probably will not be enough fermentables left in the mash for a second batch, but there is almost always enough to do something with (like make a starter or a small experimental batch). Extracting the second runnings is easy, after the wort for the first beer is collected just continue sparging into another vessel. It may seem like a chore to tack on an extra couple hours to a brew day, but think about it as saving a few hours compared to a second complete brew.
Like cooking leftovers, one thing to consider is taking the small beer in a different direction rather than making a smaller version of the big beer. With food there are a few dishes that are magnets for leftovers: sandwiches, frittatas, fried rice, and quesadillas; learn a few template recipes and you'll never throw out a hunk of roast or extra grilled vegetables again. In the same way if you keep some spare hops and yeast on hand you'll always be prepared to put second runnings to a good use.
In the case of 6.5 gallons of 1.032 wort harvested from the mash of the DCHB English Barleywine, the easiest thing to do would have been to turn it into a bitter, but I had just put my Styrian Golding Bitter on tap (not to mention that I was out of English Ale yeast). Instead I decided to open a pound of Hallertau Tradition (a higher AA% Mittelfrüh replacement) that had been sitting in my freezer for a few months and a pack of S-23 dried lager yeast to turn it into a pale session lager. I had good luck with another dried lager strain (W34/70) in a Smoked Dunkel last summer, but this was my first time using S-23. I am hoping that the toastier pale and Munich malts add some complexity in place of the clean/sweet pilsner malt that pale German lagers are usually built upon.
Hallertau Session Lager
Batch Size (Gal): 4.80
Total Grain (Lbs): 25.00
Anticipated OG: 1.042
Anticipated SRM: 14.0
Anticipated IBU: 42.5
Brewhouse Efficiency: 22 %
Wort Boil Time: 80 Minutes
62.0% - 15.50 lbs. Maris Otter
18.0% - 4.50 lbs. American Pale "2-row"
20.0% - 5.00 lbs. German Munich Malt
0.50 oz. Hallertauer Tradition (Pellet, 6.50% AA) @ 40 min.
1.00 oz. Hallertauer Tradition (Pellet, 6.50% AA) @ 20 min.
1.00 oz. Hallertauer Tradition (Pellet, 6.50% AA) @ 10 min.
1.00 oz. Hallertauer Tradition (Pellet, 6.50% AA) @ 0 min.
0.50 tsp Yeast Nutrient @ 15 min.(boil)
0.50 Whirlfloc @ 15 min.(boil)
SafLager S-23 W. Euro Lager
Profile: Washington DC
75 min @ 154 F
Added 6.5 gallons of 175 degree water to the DCHB 2nd Anniversary Barleywine mash, stirred and left for quite awhile before draining.
Chilled to 50 F then pitched 1 pack of rehydrated S-23. Put in fridge at 50 F ambient to ferment.
After 24 hours it seemed to be barely starting, I gave it a shake, 12 hours later it was going strong.
5/17/11 Moved out of the fridge, ambient basement temp ~65 F to finish fermenting and reduce any diacetyl. Attached an airlock.
5/29/11 Racked to a CO2 flushed keg for secondary. Clean, nice hop character, should do well. Put in the fridge at 34 F to lager for a few weeks.
7/4/11 Put on tap at 10 PSI to carbonate.
7/30/11 Great summer lager, with enough hop and malt to keep it interesting.