Harvest and Reuse Yeast in Homebrewing

I decided to do something a little different for my upcoming brew day: I am harvesting the yeast from my fermenting porter and using it in the stout I’ll be brewing.The only thing is, I’ve never done this before. Commercial brewers do this all the time, it’s efficient, cost-effective and helps them have a good supply of fresh, viable yeast. I’ve wanted to harvest and reuse yeast for some time now, but my beer making activities have never lined up regularly enough to do this. Prior to starting the blog my brew days were too far apart to harvest and still have clean and viable yeast when I was ready to use it.

But now the stars have aligned and I not only have an appropriate brew day coming up, I also have an appropriate batch in primary ready to go to secondary. Time to harvest!

Why Harvest and Reuse Yeast?

Why not? Aside from cost savings and the ability to get good active yeast, homebrewing to me is one big experiment about what you CAN do yourself. Is it a little more risky than just buying your yeast? Yes, but no more crazy than pouring a bunch of sugar water into a glass container along with some microorganisms, letting it for a couple weeks and then drinking the result. Sure you could buy yeast every time, or buy all of your equipment fully made, but you could also just go and buy your own craft beer if you like. That would certainly be a lot easier and probably cheaper after everything is said and done. But no, I decided to homebrew my beer for several reasons not the least of which is I want to see if I can do it!

Aside from the philosophical reason for harvesting your own yeast, there is the matter of cost saving. For me at my homebrew store the average grain is $2/lb, hops are $2.50-$3/oz and yeast is $9-10 or so. In a standard beer I’ll use 10-15lbs of grain, 2-5 oz of hops which come to $25-$45 plus the yeast at around $10. Not having to buy yeast is a 20-30% savings or so. Again I don’t homebrew for the cost savings but I’m also not about throwing money away for nothing.

When is it a good idea to Reuse Yeast?

Technically you can harvest any yeast and use it in any next batch though there are some general things to keep in mind:

  1. Yeast should be of the same type you want to brew next – you’re not going to get an ale if you pitch lager yeast and vice versa.
  2. Make sure the yeast matches the style you want to brew – don’t use a yeast that gives lots of nice fruity banana esters from a Belgian Wit in an Irish Red. The resulting beer won’t turn out good and wasted beer is a shame.
  3. The beer you’re planning to make should be similar to the beer you’re harvesting from – or at least not vastly different. Hop, roast and other strong flavors will be passed to the next beer and can create some undesirable effects. You wouldn’t want to harvest from an imperial stout and pitch into a pale ale, even if you would use the same yeast otherwise.
  4. Your next brew day is soon – with the techniques we’ll be using to keep the yeast if you’re not re-pitching soon you’ll have problems with contamination and dead yeast. Ideally you would re-pitch within 3 days or so and no more than 2 weeks.

How to Harvest and Reuse Yeast

So you’ve decided you want to try and harvest and wash your yeast. Great! Now what? Well first thing I did was see what resources existed out there currently. I found two really good resources from Brew Your Own and Beersmith. After reading these and a couple others I had worked out what I was going to do. The yeast I was moving was WLP002 English Ale Yeast from the Robust Porter I brewed previously. These were the steps I followed:

Equipment

  • Erlenmeyer flask or other container
  • Siphoning tool
  • Mason jars
  • Saucepan
  • Aluminum foil
  1. Sanitize everything with your sanitizer of choice. I use Star-San, you can use what you like.
  2. Start some water boiling (2-3 quarts should do) in the saucepan. After it’s boiled for 10 minutes cool it down to room temperature. You’ll need this later.

    Transferring Porter to Secondary Fermenter

    Transferring Porter to Secondary Fermenter

  3. Transfer your beer to the secondary fermenter using your siphon method of choice. As mentioned previously I only use the auto-siphon.

    Relax! Have a homebrew!

    Relax! Have a homebrew!

  4. Relax, have a home brew!

    Measuring fermentation progress with specific gravity.

    Don’t forget to take a sample and measure the specific gravity so you can monitor fermentation progress!

  5. Once the transfer is complete, place airlock on secondary and tend to the yeast at the bottom of the primary.
  6. You now have the nasty looking yeast cake at the bottom of the fermenter. If there is not enough beer remaining in the bottom of the fermenter to allow the yeast to pour, add some of your boiled and cooled water to the fermenter and swirl around to make a slurry.

    Harvest yeast cake into sanitized mason jars

    Pouring yeast cake into sanitized mason jars. I should have added water to this, but I didn’t and now we all know what it looks like.

  7. Sanitize the top of the fermenter with some kind of cheap alcohol and pour some of the yeast cake into your mason jars. I really should have done a couple things differently here. First, I should have added water to the fermenter to make the yeast into more of a suspension. I did not and now we get to make poop jokes. Second, I should’ve used larger mason jars, I just couldn’t find the larger ones we have so I used these. Ideally, you’d only fill the jars about 1/3 full, but no more than 1/2 full.
  8. Now that you have some questionable looking substance in your mason jars, if you did not already add boiled and cooled water to the yeast add some to the jars now. Place sanitized aluminum foil over the tops of the jars and swirl the yeast cake into suspension.

    Yeast suspension after refrigeration

    Yeast suspension after refrigeration.

  9. Place the yeast suspension into the refrigerator and set a timer for 20 minutes. The dead yeast cells and hop trub in the yeast cake will drop out of suspension and settle first leaving only healthy yeast cells in the fluid on top. If you let the suspension cool for longer than 20 minutes, the good yeast cells may start to settle as well and then you’d have to do this all over again.

    Pour yeast suspension into erlenmeyer flask

    Pour yeast suspension into erlenmeyer flask

  10. When you pull the yeast out of the fridge after 20 minutes you should have a layer of liquid on top of a layer of solids. You’ll want to carefully pour the liquid off of the solids into your sanitized starter container. Try to minimize the amount of solid you get into the starter but it’s not the end of the world if a little gets in.
  11. Put a stopper on the flask. If you’re brewing in the next couple days, go ahead and make a starter with this. If your brew day is more than a few days away then place this in the refrigerator until your brew day is closer and then make a starter.

What I learned and what I will do differently:

I learned a lot of things doing this the first time. The biggest thing is, it wasn’t that hard! I will try to plan as many of my future brew days as possible so that I can do this for all of them. Since my goal is to brew one example of every style, I will probably stick to a specific style for a while and brew those consecutively from mild flavor to strong (like English Ales, German Lagers, etc.). This has also given me the motivation to try harvesting yeast from a commercial beer, which I’m sure I’ll do in a later post.

Everything appears to have worked out with what I did, the starter was bubbling away and when I pitched this into my wort on brew day I had a good fermentation going in about 18 hours. That said, while it seems to have worked (time will tell when I taste the beer) there are a lot of things I think I’ll do differently in the future:

  1. Use a larger container to collect yeast cake from fermenter – what I used worked fine but a larger jar would have been easier to manage.
  2. Make sure there is enough fluid on the yeast cake to suspend it – because I did not have enough fluid, I think my slurry was a little thin and it took a while for the starter to get going. Once it did it was fine, but I was a little worried for a couple days.
  3. Harvest the yeast sooner – due to time constraints I left the porter in primary for about 10 days. As a result, fermentation activity was very low when I went to transfer to secondary and harvest. I probably would have harvested more yeast if I would have planned to harvest after about 5 days while there was still some fermentation activity going.
  4. Harvest from the starter – aside from having to keep them for a longer time, this seems like a great idea. Starter wort does not contain any hops and does not have any strong flavors or color which would prevent all of the problems with harvesting from one style and pitching into another. The low alcohol and hop content means the yeast has not really been stressed and is still very healthy. The yeast has not replicated many times and therefore has a reduced chance of mutation or contamination. I will likely try this with the next batch I brew.

I hope you can learn something from my experience and I hope this has motivated you to want to give yeast harvesting a try. It really isn’t as hard as it seems and seems to work well while being a nice way to save money.

Let me know if you harvest your yeast and what things you do differently!

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