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Reusing yeast at home is something I'm incredibly interested in, but haven't found the time to learn enough about it just yet.

What are the basic steps for harvesting, cultivating, or whatever other term you want to use, in order to reuse yeast from previous batches of homebrew?

What equipment is required?

What equipment is helpful, but not necessary?

What are some of the most important things to watch out for?

What other advice can you give on the topic?

What are some other resources that might help the homebrew yeast cultivator?

EDIT

More questions, from JackSmith:

Do you do anything differently when you know you're going to harvest your yeast?

Do you filter out hop sediment when you usually don't?

Do you only harvest yeast from neutral-flavored light beers?

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Extremely interested in this! –  Taylor Mar 9 '10 at 16:48
    
I don't think this warrants a separate question, so I'll ask that you edit this one to add it: Do you do anything differently when you know you're going to harvest your yeast? Do you filter out hop sediment when you usually don't? Do you only harvest yeast from neutral-flavored light beers? –  JackSmith Mar 9 '10 at 20:59
    
I try not to cultivate yeast from fruit beers, that's about it. –  topfermented Mar 10 '10 at 0:10
    
+1 Good question –  Room3 Mar 16 '10 at 18:15

4 Answers 4

up vote 18 down vote accepted

I started cropping and repitching from my third batch ever. It is not hard at all, actually results in better beer, saves money, and is kinda fun. You get to use flasks and pour stuff back and forth and rub your chin and look wise.

This article from the Wyeast people is geared toward commercial breweries, but I learned a lot about cropping from it.

I basically followed the steps here, but with some of my own tweaks. I also used the invaluable pitching rate calculator at MrMalty.com.

Short version

Save some slurry from primary, thin it with water, let settle in fridge.

Discard the top third (water), save the middle third (yeast) and discard the bottom third (trub).

The saved slurry is still a little thin for storage. Let it settle in the fridge overnight, then discard all but a bit of water, then swirl the rest so that it's pourable into a clear bottle for long-term storage.

Long version

Well before you rack, boil some water and let it cool to room temperature. You use boiled cooled water not just for sanitation, but to keep the yeast dormant by depriving them of oxygen.

Here's how I did it at racking time (keep boiled cooled water on hand):

  1. Rack from primary.
  2. Gently swirl the tiny bit of beer left to break apart the yeast cake and mix it into a slurry.
  3. Pour a generous amount of slurry into a sanitized straight-sided jar or beaker (not an Erlenmeyer flask... see below). Don't worry if you get hop remnants in there. We're going to leave them behind.
  4. Let the jar settle in the fridge while you clean your carboy.
  5. Discard the top layer of water, pour about half the remaining stuff into a sanitized Erlenmeyer flask (or just another jar).
  6. Top up the flask to about halfway with cold water, swirl, and let sit for a good half-hour in the fridge.
  7. Pour off almost all the liquid to get as thick a slurry as possible, swirl to mix the rest with the settled yeast, pour as much of the slurry as will fit into a sanitized clear glass 12 oz. bottle. Cap this bottle. (You want the clear glass to assess yeast color. You don't have to worry about light-struck flavors here as all the hop compounds which get skunky have hopefully been washed away.)
  8. Label with yeast strain, generation, and the cropping date. Keep in the back of the fridge for up to a month.

I don't use Erlenmeyer flasks for separating out the middle third of the slurry because they're very good at pouring a cross-section of the entire contents of the flask. That's what we don't want for the first step. We want to be able to control which "slice" of the yeast we get, so we avoid both water and trub. Beakers or straight-sided jars are better for this.

If you're using it within four weeks, assuming you get about a half-bottle of settled-out yeast, pitching just the slurry should work for beers up to about 1.060, assuming a 5 gallon batch.

Shortest versions

  • Pour your next batch down on your yeast cake. Others will tell you this is a bad idea, because it's overpitching and will affect the esters and head retention. I tested that hypothesis by intentionally overpitching, and found no evidence of muted esters or poor head retention. I make excellent beer regularly with this method, and it's easy.
  • Use dried yeast. Seriously, it's cheap, makes wonderful beer, and you can keep a bunch of varieties around for years. Why go through all these steps when you don't have to? A huge number of commercial brewers use dried yeast.
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To answer the extra questions: I don't do anything different. Hop sediment is not an issue with this method. I've only done it with English ale and Kolsch, so don't know if you need to brew lighter beers. If I wanted to use repitching in a monster beer, I'd repitch into a lower gravity beer to create a yeast cake first. –  Rich Armstrong Mar 10 '10 at 4:50
    
I don't get this post. It suggests the opposite to what is says in chapters 6-8 of John Palmer. He clearly states that you keep the yeast suspended in water and throw away the remaining trub. Here we are told to keep the rinsed trub/slurry and throw away the water. Which is correct? –  Poshpaws Sep 12 '11 at 14:07
    
These steps are confusing. I will edit. –  Rich Armstrong Sep 15 '11 at 16:15

I've been listening to Basic Brewing Radio. Here are some episodes about reusing yeast.

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Well, the easiest way to re-use yeast is to brew a new batch on the same day that you're transferring another batch into kegs/bottles and then rack the new wort onto the leftover yeast cake. Bam. You've re-used yeast.

At home, I have a handful of Erlenmeyer flasks and extra stoppers. Basically what I do is make a mini-starter with the yeast that's dropped out of secondary fermentation. Once that fermentation looks finished, I throw the whole flask in my beer fridge. I've been able to keep yeasts for months.

The IPA that I have going at home right now is made from yeast that I pulled out of a barleywine that I made in August.

The main thing you need to watch out for is bad sanitation (like any other aspect of brewing) and yeast stress, which may cause mutation.

Causes of yeast stress: Under-pitching yeast in high-gravity worts, high temperatures, low oxygenation (or at least, low source of fatty acids for cell wall growth) among others.

The yeast section in Fix's book The Principles of Brewing Science is an excellent source of information in what your yeast is actually doing and, thus, how to keep it healthy.

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So you typically save the yeast from your secondary and not your primary? –  JackSmith Mar 9 '10 at 18:12
    
When I go to secondary, yes. After primary you tend to have a lot of other crap in your trub - proteins, hop particles, etc. You get them in secondary, as well, but not as much. –  topfermented Mar 10 '10 at 0:07

If you use an open fermenter like I do, you may find this technique useful in salvaging yeast.

http://backyardbrewer.blogspot.com/2009/03/3-simple-homebrewing-tricks.html

mark

www.backyardbrewer.blogspot.com

www.thebackyardbrewer.com

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