What if I told you, I only take original and terminal gravity readings and that is only for quality control reasons? A yeast culture will tell you when it is finished fermenting. if you are using an airlock and the temperature of the green beer is not rising (hence, allowing CO2 gas to come out of solution), airlock activity will slow to a crawl, eventually stop and the green beer will start to clear. Far too many amateur brewers have adopted crash cooling in order to get a culture to drop out of suspension. Crash cooling may be necessary for professional brewers in order to meet production schedule demands, but it is absolutely an unnecessary step for amateur brewers. The culture will floc and drop clear when it is done. Some powdery (i.e., low to non-flocculating) strains take longer to drop than others, but they will drop if given enough time. If a culture is in suspension, it still has work to do; therefore, patience is a virtue.