If you practice good sanitation and preferably in a container that can be air-locked, you shouldn't have any problems with wild yeast, bacteria, and other nasties. I also agree with the other folks that you should trust your 5 senses. If it looks bad, smells terrible, and tastes bad (if you dare to taste your possibly infected starter) then it probably is bad. Why risk ruining 5 gallons (or whatever size batch you're making) with an infected starter. It makes better sense to just buy more yeast and pitch it direct. I do this with many of my beers. A beer with a gravity of 1.050 or higher, I pitch 2 packages of dry, or liquid yeast. For me, I love to use slurry from a previous batch. Not only does it have ample healthy yeast, but it's already paid for. If I'm making a batch that would need the same yeast as the previous batch, I'll very carefully run my chilled wort right into the same primary as a previous batch, onto the yeast cake, and aerate thoroughly, given the new beer calls for that yeast and on brew day it is time to rack the original beer. I've practiced this many times and always with great results. And, it'll save you a few bucks. Back to the thread: A starter is a wonderful idea and in many brewers opinions a must for every batch. However, every extra process you engage in making your beer the more chances that your beer can pick up bad stuff. If you are really uncertain, I'd buy 2 packs of yeast, and skip the starter all together. Besides, each pack of yeast you buy contains the baseline minimum of yeast to get a 5 gallon batch to ferment, so don't worry about over pitching. As a matter of fact, if you use only one pack of yeast no matter what style you are under pitching anyway. This is the equation Commercial breweries and myself use: 1 million yeast cells per degree Plato per milliliter of wort. If you don't use Plato, then for purpose of ease, assume degrees Plato are equal to specific gravity divided by four. Do the math. You'll be surprised at the results. Under pitching is a widespread issue, that many home brewers don't even know about or acknowledge. Seriously. Do the math.