Cropping Yeast

Finished yeast crop

Cropping yeast is something that is very common in commercial breweries because of a regular brewing pattern and the savings that can be made not having to pay for yeast every time you brew.

This was also something I was very familiar with in a commercial setting, whether that’s cropping from the bottom of a fermenter or skimming from the top. It’s something I’d never done as a homebrewer though, partially because the cost of pitching fresh every time is not prohibitive but mostly because my brewing is irregular.

Recently though I’d taken the effort to brew with a couple of yeast strains that I really like with one of them a strain that I can’t get again, both beers finished within a day or two of each other and with a holiday scheduled in I don’t have time to get more brews on so my best option is to crop for storage.

There’s a lot of information on the internet about this but I wanted something simple and easy for anyone to do.

Important things to remember

  • Cleanliness is key
  • Yeast washing

I can’t stress enough how important cleanliness is in all aspects of brewing, yeast cropping and storage is no different. I’m cleaning all my equipment with a chlorinated detergent, sanitising with a no rinse sanitiser and spraying everything with an alcohol spray sanitiser.

I washed my yeast in this instance, not in the commercial brewery sense where they lower the pH to inactivate bacteria but in the sense that cropping from the bottom includes a lot of Trub, hops and dead yeast cells, I don’t want that in my yeast culture.

It’s essentially a simple procedure:

  1. I racked off the beer from both fermenters to keg/bottle
  2. I swirled the yeast in the bottom of each fermenter to homogenise and make it easy to pour
  3. From one fermenter I poured the yeast slurry out directly through the tap, the other I poured out of the top, I put them both in the fridge and this is what I got (one of the samples)

Yeast slurry

 

  1. I then decanted the remaining beer from the sample leaving me with this.

Decanted yeast slurry

  1. I then added 500ml of boiled and cooled water, homogenised it and returned to the fridge.
  2. As you can see there are three distinct layers, top layer is yeasty water, middle layer is clean yeast with a darkly speckled trub layer at the bottom.

Decanted yeast with multiple layers

7. I then decanted the water off to the drain, decanted the clean yeast layer into sanitised flasks leaving the trub behind and giving me this.

Decanted clean yeast layer

 

I’ll now store these in the fridge at between 0-2 degrees and then create a starter for them both when I’m back from my holiday and brew some more beer!

Formerly of Fullers, Thornbridge and Buxton. Now a freelance Black IPA advocate, homebrew geezer and creator of Baby Back Bacon Black IPA™

6 Comments

  • Reply January 8, 2015

    James

    I’ve loved your other blogs so far, and they have great information, but felt the need to query some stuff here as I’m just getting into yeast handling, and don’t feel that the information above chimes with my understanding of best practices.

    1. Sanitising vs Sterilisation
    You’re doing basic (albeit thorough) home brew sanitisation, but I think when it comes to yeast handling, sterilisation (via pressure cooker or tyndallization) is considerably less risky.
    Sanitisation only reduces bacteria/wild yeasts numbers down, it doesn’t remove them entirely. Sterilisation kills everything.

    2. Yeast ‘washing’.
    Breweries wash yeast with acid to reduce background bacteria. You’re not achieving this if washing with water, so are the effects of a bit of trub really so bad that you’re willing to introduce a whole new bunch of contaminants by mixing it with boiled water?
    At the very least you’re going to cause a change in the yeast by it having to adapt to the water.
    My feeling would simply be to scoop out some yeast with a sterilised spoon into a sterile container and refrigerate. When you need the yeast again you’re going to step it up anyway.

    I may be talking rubbish here, but would love to hear your thoughts.

  • Reply January 9, 2015

    Kevin

    Thanks for this James, really interesting to read your process. Out of curiosity, how do you decant the different liquids – do you simply pour the container carefully or is there some other method thats easier/safer?

  • Reply January 9, 2015

    JK

    Hi James,

    Thanks for your comment, this is the way I see it.

    1. You’re absolute correct, sterilization is the correct terminology and process that should be used, I’m in the habit of using the term ‘sanitised’ because it’s a legal requirement for us to do so in this industry. At a homebrew level I’m happy with my sanitisation method because it’s not dissimilar to my commercial brewing experience and although there’s always room for improvement, on a risk/benefit basis for a homebrewer this ‘middle of the road’ approach has value.

    2. That’s correct, the goal isn’t to wash the yeast to eliminate bacteria, I wouldn’t advocate that procedure anyway, the goal is to wash the yeast to help remove nutrients to induce a kind of hibernation state that will allow for longer term storage. I agree that the easiest way to go about things is to crop and rebrew as you would in a commercial brewery but the point of the exercise is to allow cropping and storage for longer periods, I’ve tried cropping and leaving it in the fridge for long periods of time and it results in an autolysed mess, not something I’d want to grow up for my next brew. Similarly, the removal of the detritus in favour of healthy yeast cells I believe adds value to the next brew, if I’m pitching yeast I want it to have the highest percent viability I can create rather than transferring generation after generation of dead cells.

    Cheers

    JK

  • Reply January 9, 2015

    JK

    Hi Kevin,

    I just pour the liquid carefully, alcohol spray is definitely your friend doing this, before and after taking care to sanitise the rim of the vessel.

    Cheers

    JK

  • […] from James ‘Kempicus’ Kemp, late of Fuller’s, Thornbridge and Buxton breweries: this time, it’s about the nuts and bolts of cropping yeast in a domestic setting. (Features lots of graphic shots of […]

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