Freezing yeast

There are two suggested methods for freezing yeast.

Method 1

Introduction

One of the great ways to save some money on brewing is to reuse 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, yeast can be frozen allowing the brewer to build a "library" of strains.

Basic Concepts

Reuse

First, each original yeast sample should be reused a maximum of four times. Yeast begin to mutate over time, and it may change the characteristics of the strain, thus the characteristics of the brewed beer. Some experts believe that each sample can be used up to 10 times, however others don't feel that the risk is worth it.

Four re-uses may not sound like much, but it can be. The original harvest will yield four tubes for freezing, and each of these tubes can be re-used 4 times. This means that each original batch can yield a total of 16 other batches.

Sanitation

Sanitation, sanitation, sanitation. If at any time during harvesting or freezing a wild spore enters the yeast colony, that colony is ruined. Sanitation.

Sources

Yeast should only be harvested 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!

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.

Solution

The actual solution to suspend the yeast is a 50/25/25 freezing solution (50% yeast, 25% water, 25% glycerin).

Preparation/Equipment

Boil and cool a quart of water. Place the cooled water in a covered jar.

You'll also need:

• a sanitized, 1 quart jar with lid to hold the yeast slurry you've harvested.
• something to hold the harvested yeast - I use sanitized 15mL test tubes with screw tops.
• glycerin for the yeast freezing process (this protects the yeast cells, and prevents them from bursting). You can get this at any large drug store.
• a small, sanitized funnel that will fit into the mouth of your test tubes (or whatever you'll be using for the long-term storage).
• a flame source. I do my work right next to my gas burners in my kitchen. You can also purchase a small alcohol lab lamp. You need something to stop falling yeast/bacteria/mold from landing in your yeast.
• something to transfer the glycerin into the test tubes. I use a graduated pipette, you could also use a graduated eye dropper.
• a bowl of sanitizing solution. I use iodophor at a 12.5ppm solution.

Procedure

1. While racking the beer from the primary into secondary, try to keep a little of the beer in the primary. This will help resuspend the yeast. If you can't save any, pour a cup of your boiled and cooled water into your fermenter.
2. 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.
3. 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).
4. Clean the entire work area and get all extra beer making equipment out of the way.
5. While tidying up, the yeast slurry will begun to separate. To the bottom falls the heavy trub - proteins, hop residue, chunks of grain that made it from the boil, etc. The desirable lighter yeast still still be suspended at the top of the liquid.
6. If the yeast has settled too much, simply shake the jar, put it back in the fridge, and try again (it's usually ready after 10-15 mins).
7. With the sanitized funnel fill the sanitized tubes with the thin, milky liquid at the top of the jar. It's helpful to place the tubes in a small glass to keep them upright. Immediately put the cover on each filled tube and put into the fridge.
8. Take another cup of boiled and cooled water and pour it into the jar of remaining yeast slurry. Shake up the slurry, and place it in the fridge, too. Rinse the funnel and place it in the bowl of sanitizing solution.
9. In 10 to 15 minutes, the yeast in the tube will settle out. Open each tube and carefully pour off as much of the water as possible, leaving the yeast behind.
10. Now take the jar of yeast slurry (which should have separated again) and repeat the process of filling the tubes. Fill and decant the tubes 3 times until the tube is about half full with yeast.
11. With the desired amount of yeast in the tube, only pour off half of the water on top of the yeast. Draw with the pipette an amount of glycerin equal to 25% of the total volume (about 3.5 mL in my case) and put it in the tube. Close the tube immediately.
12. It's now a simple matter of shaking the tube up to mix all of the contents, and placing them in the freezer.

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 pack their samples in cold packs inside a foam cooler so that the samples don't go through the freeze/thaw cycle.

Re-using Yeast

To reanimate 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.

Final Thoughts

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.

Method 2

Introduction

Homebrewers often find they would like to have yeast at the ready, to defray costs or to be able to collect strains that are not readily available and grow them to a practical amount of yeast. I looked into yeast ranching with slants and decided the chore of sterilization and reculturing would be too much for me to handle. An excellent book on that subject is First Steps in Yeast Culture by Pierre Rajotte.

I decided to look for a different method and tried freezing yeast with glycerin based upon posts on rec.crafts.brewing. My results using a frost-free freezer were a total disaster. The freeze/thaw cycle of the fridge caused the yeast to die. The idea is that when the yeast is frozen the glycerin helps to keep the cell walls of the yeast from bursting. The freeze/thaw cycle can be the kiss of death depending upon how the yeast are stored.

A few years later a brewer suggested I try a non-frost-free freezer and gave me a protocol. He used a lab freezer at –80ºF and a 15% glycerin solution. I had a regular upright freezer at work that ran about –5ºF and decided to give it a whirl.

Here is the protocol I utilized (Many thanks go out to Brad Nicholson).

Necessary materials and equipment

• Glycerin
• Water
• Yeast slurry (from bottom of starter)
• Pipette (or other measuring method)
• Test tubes and caps (sterile, or sanitized)
• Masking tape
• Permanent marker

Procedure

The #1 thing to do is to have surfaces and equipment sanitized. Take nothing for granted.

1. Mix glycerin and water in the ratio of 30 mL glycerin to 70 mL water. This will yield a 30% glycerine solution.
2. Microwave the mixture until boiling.
3. Remove to the counter, cover with plastic wrap and allow to mixture cool to room temperature.
4. Add equal amounts of the 30% glycerin solution and the yeast slurry to the test tube. (The amount will be dependent upon the volume of the tube.)
5. Cap the tube and shake.
6. Mark a piece of masking tape with the yeast type and label the tube.
7. Freeze.

Glycerin can be purchased at most local drug stores, but can sometimes be difficult to locate in the store. Be diligent and you will find it. If in doubt, ask the pharmacist and they can point you to it.

Final Thoughts

You now have a frozen tube that is 15% glycerine and yeast. When I get a new strain, I try to make at least 3 tubes from the starter slurry. My procedure is to hold my finger on the end of a pipette and stick into the slurry and remove my finger allowing the slurry to be sucked into the pipette. I transfer that into the test tube as many times as necessary.

My yeast samples were kept frozen in the freezer, but eventually I had to remove them from my employer to the house. I put them into a cooler with ice packs and brought home. I then placed them into a thick foam cooler with frozen ice packs to prevent the freeze thaw cycle of the frost-free freezer from killing the yeast. Recently I revived the yeast by putting them on a stir plate with a small amount of starter wort and gradually adding more wort over time. The yeast revived perfectly after more than a year of frozen storage. The only caveat is the yeast had to grow so the results took longer than yeast abuse.

External Links

• Method 1 is from schwedhelm.net The pictures they provide there help you understand the process a bit more.

• Method 2 is from ipass.net