Originally Posted by enkamania
I just brewed Sunday, so it will be a few weeks. I can tell you the beer in the bottle looks like beer, thick layer of krausen on top
I actually posted a different thread with the same question, wasn't getting too many reponses with this one. Anyway, a Senior Member, ThatGuyRyan responded with the following answer: "I really wouldnt trust that. Fermentation depends on a lot of things and total volume, shape of fermenter, temperature all factor in. It may be close but I dont know how accurate it would be. I wouldnt do it IMO. Taking 2-3 gravity samples during the normal fermentation process 10+ days in really isnt harmful to your beer as long as you take your normal precautions. By the time you start to pull samples you should be fairly fermented out and the alcohol content give the beer a fair amount of protection. Just take the amount of samples needed to confirm fermentation is complete no more and use sanitized equipment while trying not to disturb the beer."
But I think that I'll do what you said and check it both ways to see how close the two readings are, I dunno.