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Reusing Yeast Safely

After fermentation is over its pretty tempting to reuse the cake of all that good yeast you have.  I like to reuse US-05 (fermentis) because it really seems to perform extremely well on repitch.  It seems to attenuate a little better, flocculate a little better, and it certainly gets an even cleaner flavor.  I tend to collect some slurry on the same day I plan to repitch into a new batch.  So I don’t store the yeast for any appreciable time.

Many brewers really like the idea of collecting yeast slurry from a batch and saving it for a future brew date.   I don’t do this too often because I think the process of handling the yeast, transferring it from container to container, making a new starter and then repitching just seems risky.  The number of steps increase the number of opportunities to contaminate your yeast with foreign microbes.  I ask myself, is it worth a $30-$40 batch of ingredients to save $6-$8 on a new pitch of yeast?  For me it’s not.

Recently, I have read more and more about brewers collecting, storing and repitching successfully.  Certainly, it can be done (as many brewers do it already).  But I think that for the average non-microbiologist type if you get a little lax once with your handling you’ll probably pick up a minor contamination at some point.  The purpose of this post is not to discourage people from experimenting with yeast management at home.   Rather, I wanted to relate my perceived risk to cost ratio and offer a couple easy steps to try and maintain cleanliness.

Maintaining cleanliness:

  1. Sanitize more containers than you think you need.  If you are going to collect yeast properly you’ll need to have at least two sanitize containers and some sterilized water.  I would over estimate everything by a factor of 2, so maybe for containers and a liter of boiled and cooled water.  This may seem mundane but its too easy to need another container then half-assed sanitize it because of the worry of time on catching a contaminant.
  2. Work in a clean and breeze free area.  Now, don’t think you need to sterilize your entire kitchen to do this.  Just keep your general work area free of dust.  A couple good wipes of the counters with sanitizer would be a good idea.  Keep doors and windows closed to minimize airflow.  Try and do your work when your 4 year old isn’t going to be running by every 5 minutes.  These things stir up dust which can get into your samples.
  3. Create an updraft with an alcohol lamp.  You can even use a candle or something, but if you are working with small containers just working near an open flame will keep the air moving in an upward direction, which in turn keeps things from falling into your samples.  If you want to really get fancy you can do a google search for aseptic techniques and how to “flame” an open container (not always good practice if you use mostly plastic).
  4. If you suspect you have contaminated your yeast, then don’t bother saving it.  You’ll have to taste the beer you just made before even trying to save the yeast.  You’ll need to train your palette to be more in tune with subtle off flavors.  Regardless, it may be impossible tell at such an early stage.
  5. Good yeast collection starts before you even put the first beer in the fermentor.  Most of us do a great job of cleaning and sanitizing the inside of our fermentors, but what about the outside.  There are a lot of weird lips and edges on the opening of the bucket below where the lid attaches.  At least a carboy is a little smoother.  But these areas and the outside of the lid need to be cleaned before a finished beer gets opened.  When you pry open the lid of your fermentor any dust and contaminants on the surface can get kicked up and into you beer…or yeast cake.  So be aware while you are racking the beer out you are sucking air into the fermentor.  If the lip of your fermentor or the air around you get contaminated your likelihood is veyr high that it will also get into the beer and then on the yeast cake.  That alone is something that is very hard to control (a little easier with a conical) and one of the reasons I don’t bother.

I am sure I’ll get a lot of “Oh you are worrying” too much.  Maybe I am paranoid as a guy that does this type of stuff at work regularly and works really hard to minimize contamination.  It’s still a matter of personal choice.  I think its great for people who do it regularly and I encourage anyone interested in that part of the hobby to give it a try.  For me however, I don’t get to brew as often as I like.  So when I do brew, I don’t want to lose a batch to a potentially contaminated yeast source.



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  1. I think a much better alternative is to steal some yeast from your starter (if you make one). I pitch about 85% of my starter and place the rest in a sanitized bottle, cap it and store it in the fridge. I’ve never had a problem. I think that is a much better alternative to collecting the sludge out of a fermenter.

  2. Jim

    The only advantage I see of collecting the “sludge” from a fermented beer is that the yeast have now become acclimated to that beer. For example, WL San Fran Lager yeast in a California Common recipe – this is a yeast which gets better and better with each generation, until it peaks at around the third gen. If you are saving yeast from your starter, you’ll save $$ but you aren’t getting that maturation of the yeast. Saving the $6-8 bucks per vial isn’t my motivation – having a huge amount of healthy, happy yeast to pitch is.

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