They discussed this recently on one of the brewing podcasts. Until now I had always decanted, but according to Dan Gordon of Gordon Biersch, waiting until the yeast has dropped out, is waiting too long. You want the yeast to still be in a state of logarithmic reproduction, in other words, you want them to still be eating up the O2 and reproducing, not fermenting and certainly not going dormant. If you wait until it has settled, it has to restart itself when you pitch. It was recomended to test your starter with a hydrometer and as soon as the gravity starts to drop, you know it is fermenting and has stopped reproduction, thus it is ready to pitch. It was also recomended to re-aerate after a few hours repeatedly, to insure the yeast is till reproducing not fermenting. As soon as fermentation is detected, don' aerate any more and you wont have any oxydation problems (check your starter by Hydrmeter before each time you re-aerate). Needless to say, sanitation is key during all of this.
Now this means that you would have to pitch the whole starter, no decanting, and some do say that could cause off-flavors. To remedy this, do a controlled started usind the same, or similar, DME to the malt you will be using in your brew. Example, if you are making a Munich Dunkel, use munich extract for your starter, making an IPA, use pale extract for your starter. If you contol your starter well enough, it wont have any problems, and won't affect your beer. Of course some say it is too little to really affect your beer anyway.
If done properly, you could build this starter for an ale for about three days before reproduction has stopped, and a week for a lager (if done at fermenting temperatures as it should be to avoid off flavors). Of course this adds a bit of work, to remedy this, you don't really need to test until you see the yeast beginning to flocculate. Aerate occasionally and wait for signs of settling, at this point test, if SG is dropping, your starter is done, brew soon.
Long story short, it's already fermented out, so yes decant and pitch, you still have built up the cell count, the yeasts are just napping right now. Next time, try to pitch before they go to sleep. I typed a lot.:cross:
