Top cropping question

[kanzimonson]

I'm thinking about making a batch of beer, getting it in a carboy, and begin top cropping using this method. EXCEPT, I was thinking that on the second day of fermentation, I would brew another batch (maybe a different beer, whatever), put it in its own carboy, and begin directing the top cropped yeast from the first batch right on top of the second batch.

Using Mr Malty's calculator with the Yeast Concentration set to 1 and the Non-Yeast Percentage set to 10, it looks like I would need about 300ml of yeast slurry for 5.5gal of 1.060 wort.

It seems reasonable that if I were just top cropping into a flask like in the video, I could get 300ml of slurry, so do you think there would be a problem with my experiment?

Technically the pitching rate would be off in the beginning, but would increase to the correct level. The very first top cropped yeast to hit the new wort would begin reproducing immediately and significantly, and the last yeast would probably enter a wort with a large enough yeast population. I like the idea because you really couldn't get a purer yeast culture for repitching.

 

[Wolfy]

'Pure' yeast depends mostly on your sanitation procedures and not when or how you crop it. The only time (in a home brew situation) it's really 'pure' is when it's in the unopened package. If you were top cropping in an open fermenter you'd usually skim off the top layer of brown 'gunk' and take only the clean yeast under it, that will be a more difficult in a carboy. Also depending on which yeast you are using you might find that top cropping 3-400ml means taking more than you expect.

Having said that, top cropping is a good way to harvest healthy and fresh yeast, and most likely your experiment will allow you to do that. However, depending on how (or if) different the second wort is compared to the first, the top cropped yeast may still need to adapt and acclimatize to the new conditions so the yeast may not 'hit the new wort' as happily as you might expect. In brewery situations where top cropping is (and has been for many years) a standard procedure, they are usually working with the same wort each time - which may not be the case for home brewing.