Flotation flocculation of yeast and Yeast harvesting

[perfection]

Typically, when the yeast drop out of the beer (unaided or aided with finings) we refer to it as the beer is falling bright. I am given to understand that yeast may flocculate and float (instead of sediment to the bottom) - in such case the yeast would be harvested by skimming for reuse in a subsequent fermentation.

Three queries:
- how does one harvest yeast if they settle to the bottom of a tank?
- flotation flocculation brightens the beer - is this also termed 'dropping' bright or is the term used only for sedimented yeast during and after a secondary fermentation
- do ale yeast always flocculate on top and lager yeast flocculate at the bottom?

Thanks

[dick murton]

- how does one harvest yeast if they settle to the bottom of a tank?
If you are using conical bottomed tanks - the same way as you would with a normally bottom cropping yeast - through the main inlet / outlet. However, most people would consider the settled top cropping yeast would be stressed or otherwise atypical, and so likely to produce beer which is not consistent with that produced from top harvested yeast. It is likely to contain larger proportions of dead or low viability cells. Having said that, I have used normally top cropping yeast for fermentations on occasions without too many problems - but always blended the beer off with "normal" beer.

- flotation flocculation brightens the beer - is this also termed 'dropping' bright or is the term used only for sedimented yeast during and after a secondary fermentation
Dropping bright normally refers to beer after it has been fined, or otherwise specifically conditioned to enhance the sedimentation of the yeast. Normal initial flocculation of either top cropping yeast at the end of fermentation is not generally referred to as dropping bright.

- do ale yeast always flocculate on top and lager yeast flocculate at the bottom? No, but this is most typical. I have worked with both top cropping lagers and bottom cropping ales, specifically selected for those characteristics, but depending on the fermentation conditions and timing, you can crop bottom cropping yeasts (but normally with poor slurry consistency) from the top, or top cropping yeasts from the bottom. The latter option is probably more commonly practised though.