Yeast Harvesting & Freezing
One of the great ways to save some money on your brewing hobby is to reuse your yeast from batch to batch. With the addition of some simple equipment, anyone can harvest the yeast from previous batches. With only a few additional steps, you can freeze the yeast so you are able to build a "library" of strains that you can use at your discretion.
Here are a couple rules of thumb I follow. Others may do it differently, but this has worked very well for me.
Click on any of the images for a larger, more detailed version.
First, only re-use each original yeast sample 4 times. Yeast begin to mutate over time, and it may change the characteristics of the strain, thus the characteristics of your beer. I've read text that say you can use each sample up to 10 times. This very well may work, I just don't want to risk my beer.
4 re-uses may not sound like much, but it can be. In my case, from the original harvest, I'll make 4 tubes for freezing. Each of these tubes can be re-used 4 times. This means that from each original batch, I'll get a total of 16 other batches.
Secondly, be prepared to be a psycho about cleanliness. If at any time during your harvesting or freezing, a wild spore enters your yeast colony, that colony is ruined.
Thirdly, I only harvest the yeast from the primary fermenter. The stuff in the secondary may look cleaner, but I figure that it was part of the "yeast clan" that wasn't able to do it's job when almost everyone else did there's (during the primary). I don't want any slackers in my beer!
Fourth, I use a 50/25/25 freezing solution (50% yeast, 25% water, 25% glycerin).
Finally, don't bother harvesting yeast that was originally in dry form. At a couple of dollars per package, it's just not worth the time and effort.
OK, let's get down to business. You'll need to do a little preparation in advance. You need to boil and cool a quart of water. Place the cooled water in a covered jar.
You'll also need:
After you have racked your beer from the primary into your secondary, attempt to keep a little of the beer in the primary. This will help re-suspend the yeast. If you can't save any, pour a cup of your boiled and cooled water into your fermenter.
Cover the opening (with the lid if using a bucket, or with a piece of sanitized aluminum foil if using a carboy) and swirl the fermenter until all of the yeast and trub is suspended in liquid.
Once it's all suspended, immediately fill the sanitized jar with lid to within 2 inches of the top with the yeast slurry. Cover this loosely with the lid, and place in the refrigerator (if you cover it tightly, it may burst the lid or jar).
Clean the entire area where you will be working. Get all of your beer making equipment out of the way. Clean like a psycho!
While you've been doing this, your yeast slurry has begun to separate. To the bottom falls the heavy trub - proteins, hop residue, chunks of grain that made it from the boil, etc. At the top, you'll have the lighter yeast still suspended in the liquid. This is what we want!
If the yeast has settled too much, simple shake up the jar, put it back in the fridge, and try again (it's usually ready after 10-15 mins).
Now, take your sanitized funnel, and fill your sanitized tubes with the thin, milky liquid at the top of the jar. I place my tubes in a small glass to keep them upright. Immediately put the cover on each tube as you fill it. Place these right into the fridge.
Take another cup of your boiled and cooled water, and pour it into the remaining yeast slurry. Shake up the slurry, and place it in the fridge, too. Rinse off your funnel, and place it in the bowl of sanitizing solution.
In 10 to 15 minutes, the yeast in the tube will settle out. You now want to open each tube, and pour off as much of the water as possible, leaving the yeast behind.
Now take your jar of yeast slurry (which should have separated again) and repeat the process of filling them. I do this 3 times until the tube is about half full with yeast.
Once you have the desired amount of yeast in the tube, only pour off half of the water the last time. Take your pipette and draw an amount of glycerin equal to 25% of the total (about 3 1/2 ml in my case) and put it in the tube. Close it up immediately.
It's now a simple matter of shaking the tube up to mix all of the contents, and placing them in the freezer.
Here's an important note: Most home freezers are frost free. They have a freeze/thaw cycle that will eventually thaw out your samples. Many brewers that freeze their yeast place their samples in a styrofoam cooler, loaded with freezer packs so the samples don't go through the freeze/thaw cycle.
To "re-animate" your yeast, place the frozen tube in the fridge to thaw 5 days before you will be brewing. The next day, place it in a safe location that's room temperature. The day after that, make a starter as you would for any batch. Let it go at least 2 days to allow enough of the yeast to grow for sufficient pitching rates.
When the beer is finished, repeat the harvest/freeze process up to 4 more times.
I number all of my tubes so I can keep track of them. I use an Excel spread sheet to track the strain, the number of generations the tube has been used, and when it was frozen. I've used samples up to 9 months old, and they produced excellent beer. A number of fellow brewers have used samples in excess of a year with no problems at all.
For a slightly different approach, check out the site of Mike Dixon and how he harvests and freezes yeast.
Give it try. You'll enjoy the process and the cost savings.
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