Continuing last week’s blog on top cropping yeast, this week will talk about bottom cropping yeast. This is most commonly used for lager yeast (bottom fermenting) however since many commercial and home brewers are using conical fermenters for fermentation where there is limited access to the top of the fermenter, bottom cropping is usually the easier option. Here’s how it works…

Bottom Cropping

This is the process by which yeast is collected from the bottom of the fermenter at the end of fermentation. However the timing of this is very important since as soon as yeast drop to the bottom of the fermenter they start to use their reserves and decompose, therefore they need to be collected as quickly as possible 1-2 days after initially cooling the beers. The other downside of bottom cropping is that in the bottom of the fermenter there is not only good yeast cells but also bad yeast cells, trub and hop matter. Therefore the yeast we are wanting is a little harder to collect.

To bottom crop yeast from a conical fermenter you will need;

  • Sanitiser
  • Collection vessel Plastic or Glass storage bottle around 250 ml (8 oz)
  • Suitable tubbing and fittings to connect from the bottom of your conical fermenter to the collection vessel
  • Filtered water 100 ml (3 oz) at fermentation temperature
  • If possible add positive pressure to the top of the fermentation vessel using a pressure transfer. Or vent the top of the fermenter as to not suck the sanitiser from your airlock into your beer as you drop the yeast

Method:

  1. First sanitise all tubing, fittings and vessels.
  2. Connect your tubbing to the bottom tap of your conical or the upper tap on the Grainfather dual tap.
  3. Connect your method for adding positive pressure to the top of the fermenter or loosen your bubble lock.
  4. Start dropping your yeast the first third of the yeast slurry will be trub and dead cells. Discard this third.
  5. The yeast slurry will lighten and become creamier in texture. This is the second third and is considered the best yeast for harvesting  retain this third.
  6. Add your water so that you have about 50-150 ml (1.5-4.5 oz) of ‘yeast slurry’.
  7. Loosely seal the jar with the lid or use sanitised aluminium foil store in the fridge.
  8. Ensure your sample is labelled as clearly as possible and that the jar is vented but not opened.
  9. The remaining yeast can be discarded now as this is the low flocculating yeast or can be discarded after transferring the beer.
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