After taking my OG, I pull the hydrometer out and cover the cylinder with foil. This sits on the counter for a few days. If it starts to ferment I know that there's a chance that my sanitation was not good. Maybe something wild dropped in during chilling. Whatever, it's not a big concern as long as the main batch starts before the sample. It's just a point of reference in case there's an issue with the finished beer. FG reading always get drank.
Itís best to brew dark beer at night, because that way the darkness gets into the beer. óBohuslav Hlavsa