Originally Posted by wilson1417
Your starter will take a few days to "start". But your wort will be fine sitting in fermenter with no yeast for a few days until the starter is ready if you "have" to brew tommorrow.
Your starter will be ready overnight. Typically high krausen occurs 16-24 hours after pitching. Starters are super fast because of the massive amount of yeast compared to the small amount of wort. If you make a smaller starter, like a 1L or so, you can pitch the whole thing into the wort to be fermented at high krausen. However, if you make a larger starter like a 2 L starter, you would probably want to let the starter ferment out completely for 2 days, then chill for a few days in the fridge to force the yeast to drop out of suspension, then on the day to pitch decant the liquid off the top and allow the yeast cake to warm up to room temperature before pitching. The idea behind decanting off the liquid is because when you make a starter you really want to aerate it (which promotes yeast reproduction) but the resulting "beer" is oxidized. Therefore, you don't want to pitch 2L of oxidized, unhopped, liquid into your beer. However, many experienced brewers, including Jamil Z., say that a 1L starter is fine to pitch directly into your wort (assuming you do so at high krausen). This is the method I use 90% of the time because I primarily make 1L starters. Some brewers will always do the decant method because they don't want to put any oxidized liquid into their beer. There is certainly nothing wrong with this approach, but I personally like the high krausen method because the yeast are active and ready to go.
Also, although you can sometimes get away with leaving a wort sit covered for a day or so without pitching, but the longer you wait, the longer nasties like infections or wild yeast, have an opportunity to establish a beach head in your beer... this method didn't work out so well for the Germans in WWII.