How do yeast work? Evenly?

[Redpiper]

Whenever I take a gravity reading through the spout on my bucket, I always wonder if there is the possibility that what's at the bottom of the bucket might have a different gravity than what's at the middle or top. So with regular ale yeast, does anyone know the dynamics of fermentation? Do they work their way down? Move all around? And how do hop particles or krausen factor in if they've settled out and mix into the sample?

 

[TipsyDragon]

your over thinking things. the beer in your bucket is all one density. if it wasn't when you started it will be by the time the yeast get going and definitely by the time they finish. any "particles" only displace liquid not change its density which is what your hydrometer is measuring.

 

[Redpiper]

Yeah, I do tend to think too much, though it's really in the interest of learning.

Practically I leave the primary going 3-4 weeks, check the FG before I bottle. It's always matched the target by then and I've proceeded without really worrying about it. It's just a thought that's crossed my mind, especially on the boards with all the questions about when beer is ready or when someone is looking to move quickly to a secondary.

 

[kanzimonson]

Yeah it's really only in any stage in which different gravity worts are mixing that you have to be concerned. So we're talking about running off from the mash into the kettle, or adding water to a batch.